chapter X., the presence of this property is an indication that the
matter is undergoing change accompanied by the expulsion of charged particles. It does not, however, by any means follow that because the atom of one element in the course of time becomes unstable and breaks up, that, therefore, the atoms of all the other elements pass through similar phases of instability.
It has already been mentioned (section 8), that Mme Curie made a very extensive examination of most of the elements and their compounds for radio-activity. The electric method was used, and any substance possessing an activity of ¹⁄₁₀₀ of that of uranium would certainly have been detected. With the exception of the known radio-elements and the minerals containing uranium and thorium, no other substances were found to be radio-active even to that degree.
Certain substances like phosphorus[435] possess the property of ionizing a gas under special conditions. The air which is drawn over the phosphorus is conducting, but it has not yet been settled whether this conductivity is due merely to ions formed at the surface of the phosphorus or to ions produced by the phosphorus nuclei or emanations, as they have been termed, which are carried along with the current of air. It does not however appear that the ionization of the gas is in any way due to the presence of a penetrating type of radiation such as is emitted by the radio-active bodies. Le Bon (section 8) observed that quinine sulphate, after being heated to a temperature below the melting point and then allowed to cool, showed for a time strong phosphorescence and was able rapidly to discharge an electroscope. The discharging action of quinine sulphate under varying conditions has been very carefully examined by Miss Gates[436]. The ionization could not be observed through thin aluminium foil or gold-leaf, but appeared to be confined to the surface of the sulphate. The current observed by an electrometer was found to vary with the direction of the electric field, indicating that the positive and negative ions had very different mobilities. The discharging action appears to be due either to an ionization of the gas very close to the surface by some short ultra-violet light waves, accompanying the phosphorescence, or to a chemical action taking place at the surface.
Thus, neither phosphorus nor quinine sulphate can be considered to be radio-active, even under the special conditions when they are able to discharge an electrified body. No evidence in either case has been found that the ionization is due to the emission of a penetrating radiation.
No certain evidence has yet been obtained that any body can be made radio-active by exposure to Röntgen rays or cathode rays. A metal exposed to the action of Röntgen rays gives rise to a secondary radiation which is very readily absorbed in a few centimetres of air. It is possible that this secondary radiation may prove to be analogous in some respects to the α rays from the radio-elements. The secondary radiation, however, ceases immediately the Röntgen rays are cut off. Villard[437] stated that a piece of bismuth produced a feeble photographic action after it had been exposed for some time to the action of the cathode rays in a vacuum. It has not however been shown that the bismuth gives out rays of a character similar to those of the radio-active bodies. The experiments of Ramsay and Cooke on the production of apparent activity in inactive matter by the radiations from radium have already been discussed in section 264.
The existence of a very feeble radio-activity of ordinary matter has been deduced from the study of the conductivity of gases in closed vessels. The conductivity is extremely minute, and special methods are required to determine it with accuracy. A brief account will now be given of the gradual growth of our knowledge on this important question.
=284. Conductivity of air in closed vessels.= Since the time of Coulomb onwards several investigators have believed that a charged conductor placed inside a closed vessel lost its charge more rapidly than could be explained by the conduction leak across the insulating support. Matteucci, as early as 1850, observed that the rate of loss of charge was independent of the potential. Boys, by using quartz insulators of different lengths and diameters, arrived at the conclusion that the leakage must in part take place through the air. This loss of charge in a closed vessel was believed to be due in some way to the presence of dust particles in the air.
On the discovery that gases become temporary conductors of electricity under the influence of Röntgen rays and the rays from radio-active substances, attention was again drawn to this question. Geitel[438] and C. T. R. Wilson[439] independently attacked the problem, and both came to the conclusion that the loss of charge was due to a constant ionization of the air in the closed vessel. Geitel employed in his experiments an apparatus similar to that shown in Fig. 103. The loss of charge of an Exner electroscope, with the cylinder of wire netting _Z_ attached, was observed in a closed vessel containing about 30 litres of air. The electroscope system was found to diminish in potential at the rate of about 40 volts per hour, and this leakage was shown not to be due to a want of insulation of the supports.
Wilson, on the other hand, used a vessel of very small volume, in order to work with air which could be completely freed from dust. In the first experiments a silvered glass vessel with a volume of only 163 c.c. was employed. The experimental arrangement is shown in Fig. 104.
The conductor, of which the loss of charge was to be measured, was placed near the centre of the vessel _A_. It consisted of a narrow strip of metal with a gold-leaf attached. The strip of metal was fixed to the upper rod by means of a small sulphur bead. The upper rod was connected with a sulphur condenser with an Exner electroscope _B_ attached to indicate its potential. The gold-leaf system was initially charged to the same potential as the upper rod and condenser by means of a fine steel wire which was caused to touch the gold-leaf system by the attraction of a magnet brought near it. The rate of movement of the gold-leaf was measured by means of a microscope provided with a micrometer eye-piece. By keeping the upper rod at a slightly higher potential than the gold-leaf system, it was ensured that the loss of charge of the gold-leaf system should not be due in any way to a conduction leakage across the sulphur bead.
The method employed by Wilson in these experiments is very certain and convenient when an extremely small rate of discharge is to be observed. In this respect the electroscope measures with certainty a rate of loss of charge much smaller than can be measured by a sensitive electrometer.
Both Geitel and Wilson found that the leakage of the insulated system in dust-free air was the same for a positive as for a negative charge, and was independent of the potential over a considerable range. The leakage was the same in the dark as in diffuse daylight. The independence of leakage of the potential is strong evidence that the loss of charge is due to a constant ionization of the air. When the electric field acting on the gas exceeds a certain value, all the ions are carried to the electrodes before recombination occurs. A saturation current is reached, and it will be independent of further increase of the electric field, provided, of course, a potential sufficiently high to cause a spark to pass is not applied.
C. T. R. Wilson has recently devised a striking experiment to show the presence of ions in dust-free air which is not exposed to any external ionizing agency. Two large metal plates are placed in a glass vessel connected with an expansion apparatus similar to that described in section 34. On expanding the air, the presence of the ions is shown by the appearance of a slight cloud between the plates. These condensation nuclei carry an electric charge, and are apparently similar in all respects to the ions produced in gases by X rays, or by the rays from active substances.
Wilson found that the loss of charge of the insulated system was independent of the locality. The rate of discharge was unaltered when the apparatus was placed in a deep tunnel, so that it did not appear that the loss of charge was due to an external radiation. From experiments already described, however (section 279), it is probable that about 30 per cent. of the rate of discharge observed was due to a very penetrating radiation. This experiment of Wilson’s indicates that the intensity of the penetrating radiation was the same in the tunnel as at the earth’s surface. Wilson found that the ionization of the air was about the same in a brass vessel as in one of glass, and came to the conclusion that the air was spontaneously ionized.
Using a brass vessel of volume about 471 c.c., Wilson determined the number of ions that must be produced in air per unit volume per second, in order to account for the loss of charge of the insulated system. The leakage system was found to have a capacity of about 1·1 electrostatic units, and lost its charge at the rate of 4·1 volts per hour for a potential of 210 volts, and 4·0 volts per hour for a potential of 120 volts. Taking the charge on an ion as 3·4 × 10⁻¹⁰ electrostatic units, this corresponds to a production of 26 ions per second.
Rutherford and Allan[440] repeated the results of Geitel and Wilson, using an electrometer method. The saturation current was observed between two concentric zinc cylinders of diameter 25·5 and 7·5 cms. respectively and length 154 cms. It was found that the saturation current could practically be obtained with a potential of a few volts. Saturation was however obtained with a lower voltage after the air had remained undisturbed in the cylinders for several days. This was probably due to the gradual settling of the dust originally present in the air.
Later observations of the number of ions produced in air in sealed vessels have been made by Patterson[441], Harms[442], and Cooke[443]. The results obtained by different observers are shown in the following table. The value of the charge on an ion is taken as 3·4 × 10⁻¹⁰ electrostatic units:
Material of Number of ions Observer vessel produced per c.c. per second
Silvered 36 C. T. R. Wilson glass
Brass 26 „ „
Zinc 27 Rutherford and Allan
Glass 53 to 63 Harms
Iron 61 Patterson
Cleaned 10 Cooke brass
It will be shown later that the differences in these results are probably due to differences in the radio-activity of the containing vessel.
=285. Effect of pressure and nature of gas.= C. T. R. Wilson (_loc. cit._) found that the rate of leakage of a charged conductor varied approximately as the pressure of the air between the pressures examined, viz. 43 mms. and 743 mms. of mercury. These results point to the conclusion that, in a good vacuum, a charged body would lose its charge extremely slowly. This is in agreement with an observation of Crookes, who found that a pair of gold-leaves retained their charge for several months in a high vacuum.
Wilson[444] at a later date investigated the leakage for different gases. The results are included in the following table, where the ionization produced in air is taken as unity:
Gas Relative (Relative ionization ionization) / (density)
Air 1·00 1·00
Hydrogen 0·184 2·7
Carbon dioxide 1·69 1·10
Sulphur 2·64 1·21 dioxide
Chloroform 4·7 1·09
With the exception of hydrogen, the ionization produced in different gases is approximately proportional to their density. The relative ionization is very similar to that observed by Strutt (section 45) for gases exposed to the influence of the α and β rays from radio-active substances, and points to the conclusion that the ionization observed may be due either to a radiation from the walls of the vessel or from external sources.
Jaffé[445] has made a careful examination of the natural ionization in the very heavy gas nickel-carbonyl, Ni(CO)₄, in a small silvered glass vessel. The ionization of this gas was 5·1 times that of air at normal pressure while its density is 5·9 times that of air. The leak of the electroscope was nearly proportional to the pressures except at low pressure, when the leak was somewhat greater than would be expected if the pressure law held. The fact that a gas of such high density and complicated structure behaves like the simpler and lighter gases is a strong indication that the ionization itself is due to a radiation from the walls of the vessel and not to a spontaneous ionization of the gas.
Patterson[446] examined the variation of the ionization of air with pressure in a large iron vessel of diameter 30 cms. and length 20 cms. The current between a central electrode and the cylinder was measured by means of a sensitive Dolezalek electrometer. He found that the saturation current was practically independent of the pressure for pressures greater than 300 mms. of mercury. Below a pressure of 80 mms. the current varied directly as the pressure. For air at atmospheric pressure, the current was independent of the temperature up to 450° C. With further increase of temperature, the current began to increase, and the increase was more rapid when the central electrode was charged negatively than when it was charged positively. This difference was ascribed to the production of positive ions at the surface of the iron vessel. The results obtained by Patterson render it very improbable that the ionization observed in air is due to a spontaneous ionization of the enclosed air: for we should expect the amount of this ionization to depend on the temperature of the gas. On the other hand, these results are to be expected if the ionization of the enclosed air is mainly due to an easily absorbed radiation from the walls of the vessel. If this radiation had a penetrating power about equal to that observed for the α rays of the radio-elements, the radiation would be absorbed in a few centimetres of air. With diminution of pressure, the radiations would traverse a greater distance of air before complete absorption, but the total ionization produced by the rays would still remain about the same, until the pressure was reduced sufficiently to allow the radiation to traverse the air space in the vessel without complete absorption. With still further diminution of pressure, the total ionization produced by the radiation, and in consequence the current observed, would vary directly as the pressure.
=286. Examination of ordinary matter for radio-activity.= Strutt[447], McLennan and Burton[448], and Cooke[449], independently observed about the same time that ordinary matter is radio-active to a slight degree. Strutt, by means of an electroscope, observed that the ionization produced in a closed vessel varied with the material of the vessel. A glass vessel with a removable base was employed and the vessel was lined with the material to be examined. The following table shows the relative results obtained. The amount of leakage observed is expressed in terms of the number of scale divisions of the eye-piece passed over per hour by the gold-leaf:
Material of Leakage in lining of scale divisions vessel per hour
Tinfoil 3·3
„ another 2·3 sample
Glass coated 1·3 with phosphoric acid
Silver 1·6 chemically deposited on glass
Zinc 1·2
Lead 2·2
Copper (clean) 2·3
„ (oxidized) 1·7
Platinum 2·0, 2·9, 3·9 (various samples)
Aluminium 1·4
There are thus marked differences in the leakage observed for different materials and also considerable differences in different samples of the same metal. For example, one specimen of platinum caused nearly twice the leakage of another sample from a different stock.
McLennan and Burton, on the other hand, measured by means of a sensitive electrometer the ionization current produced in the air in a closed iron cylinder 25 cms. in diameter and 130 cms. in length, in which an insulated central electrode was placed. The open cylinder was first exposed for some time at the open window of the laboratory. It was then removed, the top and bottom closed, and the saturation current through the gas determined as soon as possible. In all cases it was observed that the current diminished for two or three hours to a minimum and then very slowly increased again. In one experiment, for example, the initial current observed corresponded to 30 on an arbitrary scale. In the course of four hours the current fell to a minimum of 6·6, and 44 hours later had risen to a practical maximum of 24. The initial decrease observed is probably due to a radio-activity of the enclosed air or walls of the vessel, which decayed rapidly with the time. The decay of the excited activity produced on the interior surface of the cylinder when exposed to the air was probably responsible for a part of the decrease observed. McLennan ascribes the increase of current with time to a radio-active _emanation_ which is given off from the cylinder, and ionizes the enclosed air. On placing linings of lead, tin, and zinc in the iron cylinder, considerable differences were observed both for the minimum current and also for the final maximum. Lead gave about twice the current due to zinc, while tin gave an intermediate value. These results are similar in character to those obtained by Strutt.
McLennan and Burton also investigated the effect of diminution of pressure on the current. The cylinder was filled with air to a pressure of 7 atmospheres, and allowed to stand until the current reached a constant value. The air was then allowed to escape and the pressure reduced to 44 mms. of mercury. The current was found to vary approximately as the pressure over the whole range. These results are not in agreement with the results of Patterson already described, nor with some later experiments of Strutt. McLennan’s results however point to the conclusion that the ionization was mainly due to an emanation emitted from the metal. Since the air was rapidly removed, a proportionate amount of the emanation would be removed also, and it might thus be expected that the current would vary directly as the pressure. If this is the case the current through the gas at low pressures should increase again to a maximum if time is allowed for a fresh emanation to form.
H. L. Cooke, using an electroscopic method, obtained results very similar to those given by Strutt. Cooke observed that a penetrating radiation was given out from brick. When a brass vessel containing the gold-leaf system was surrounded by brick, the discharge of the electroscope was increased by 40 to 50 per cent. This radiation was of about the same penetrating power as the rays from radio-active substances. The rays were completely absorbed by surrounding the electroscope with a sheet of lead 2 mms. in thickness. This result is in agreement with the observation of Elster and Geitel, already mentioned, that radio-active matter was present in clay freshly dug up from the earth.
Cooke also observed that the ionization of the air in a brass electroscope could be reduced to about one-third of its usual value if the interior surface of the brass was carefully cleaned. By removing the surface of the brass he was able to reduce the ionization of the enclosed air from 30 to 10 ions per c.c. per second. This is an important observation, and indicates that a large proportion of the radio-activity observed in ordinary matter is due to a deposit of radio-active matter on its surface. It has already been shown that bodies which have been exposed in the presence of the radium emanation retain a residual activity which decays extremely slowly. There can be no doubt that the radium emanation is present in the atmosphere, and the exposed surface of matter, in consequence, will become coated with an invisible film of radio-active matter, deposited from the atmosphere. On account of the slow decay of this activity it is probable that the activity of matter exposed in the open air would steadily increase for a long interval. Metals, even if they are originally inactive, would thus acquire a fairly permanent activity, but it should be possible to get rid of this by removing the surface of the metal or by chemical treatment. The rapid increase of activity of all matter left in a laboratory in which a large quantity of emanation has been released has been drawn attention to by Eve[450]. This superficial activity, due to the products radium D, E, and F, was mainly removed by placing the metal in strong acid.
A number of experiments have been made by J. J. Thomson, N. R. Campbell, and A. Wood in the Cavendish laboratory to examine whether the radio-activity observed in ordinary matter is a specific property of such matter or is due to the presence of some radio-active impurity. An account of these experiments was given by Professor J. J. Thomson in a discussion on the Radio-activity of Ordinary Matter at the British Association meeting at Cambridge, 1904. The results[451], as a whole, support the view that each substance gives out a characteristic type or types of radiation and that the radiation is a specific property of the substance. J. J. Thomson[452] has made experiments to observe the action of different substances in cutting off the external very penetrating radiation (section 279) observed by Cooke and McLennan. He found that some substances cut off this external radiation, while others had little if any effect. For example, the ionization in a closed vessel was reduced 17 per cent. by surrounding it with a thick lead envelope; but, on surrounding it with an equivalent absorbing thickness of water, or water mixed with sand, no sensible diminution was observed. In other experiments Wood[453] found that the diminution of the ionization by a given screen depended upon the material of the vessel. For example, the ionization in a lead vessel, surrounded by a lead screen, was reduced 10 per cent., while in an iron vessel it was reduced 24 per cent. He concludes from his experiments that the ionization observed in a closed vessel has a threefold origin. Part of it is due to an external penetrating radiation, part to a secondary radiation set up by it, while the remainder is due to an intrinsic radiation from the walls, altogether independent of the external radiation.
In some experiments of Campbell[454], the variation of the ionization current between two parallel plates was observed for a progressive increase of the distance between them. The effects observed are shown in Fig. 105. The curves at first rise rapidly, then bend over and finally become a straight line. The knee of the curve is at a different distance for the different substances. The shape of these curves indicates that two types of radiation are present, one of which is readily absorbed in the gas while the other, a more penetrating type of radiation, extends over the whole distance between the plates. In another series of experiments, one side of the testing vessel was of thin aluminium, and the ionization current was observed when an exterior screen was brought up to it. Lead gave a considerable increase, but the radiation from it was readily absorbed by an interposed screen. The radiation emitted by carbon and zinc was more than twice as penetrating as from lead.
Attempts were made to see whether a radio-active emanation was given off by dissolving solid substances and then keeping the solutions in a closed vessel and afterwards testing the activity of the air drawn from them. In some cases an emanation was observed, but the amount varied with different specimens of the same material; in others no effect was detected.
When linings of different substances were placed in a closed testing vessel, the ionization current in most cases fell at first, passed through a minimum, and then slowly increased to a maximum. For lead the maximum was reached in 9 hours, for tin in 14 and for zinc in 18 hours. These results indicate that an emanation is given off from the metal, and that the amount reaches a maximum value at different intervals in the various cases. This was confirmed by an examination of a piece of lead which was left in radium-free nitric acid. Twenty times the normal effect was observed after this treatment. This is probably due to the increase of porosity of the lead which allows a greater fraction of the emanation produced in the metal to diffuse out with the gas.
The activity observed in ordinary matter is extremely small. The lowest rate of production of ions yet observed is 10 per cubic centimetre per second in a brass vessel. Suppose a spherical brass vessel is taken of capacity 1 litre. The area of the interior surface would be about 480 sq. cms. and the total number of ions produced per second would be about 10⁴. Now it has been shown, in section 252, that an α particle projected from radium itself gives rise to 8·6 × 10⁴ ions before it is absorbed in the gas. An expulsion of one α particle every 8 seconds from the whole vessel, or of one α particle from each square centimetre of surface _per hour_ would thus account for the minute conductivity observed. Even if it were supposed that this activity is the result of a breaking up of the matter composing the vessel, the disintegration of one atom per second per gram, provided it was accompanied by the expulsion of an α particle, would fully account for the conductivity observed.
While the experiments, already referred to, afford strong evidence that ordinary matter does possess the property of radio-activity to a feeble degree, it must not be forgotten that the activity observed is excessively minute, compared even with a weak radio-active substance like uranium or thorium. The interpretation of the results is complicated, too, by the presence of the radium emanation in the atmosphere, for we have seen that the surface of every body exposed to the open air must become coated with the slowly changing transformation products of the radium emanation. The distribution of radio-active matter throughout the constituents of the earth renders it difficult to be certain that any substance, however carefully prepared, is freed from radio-active impurities. If matter in general is radio-active, it must be undergoing transformation at an excessively slow rate, unless it be supposed (see Appendix A) that changes of a similar character to those observed in the radio-elements may occur without the appearance of their characteristic radiations.
Footnote 384:
Geitel, _Phys. Zeit._ 2, p. 116, 1900.
Footnote 385:
C. T. R. Wilson, _Proc. Camb. Phil. Soc._ 11, p. 32, 1900. _Proc. Roy. Soc._ 68, p. 151, 1901.
Footnote 386:
Elster and Geitel, _Phys. Zeit._ 2, p. 590, 1901.
Footnote 387:
Elster and Geitel, _Phys. Zeit._ 3, p. 76, 1901.
Footnote 388:
Rutherford and Allan, _Phil. Mag._ Dec. 1902.
Footnote 389:
Allan, _Phil. Mag._ Feb. 1904.
Footnote 390:
C. T. R. Wilson, _Proc. Camb. Phil. Soc._ 11, p. 428, 1902.
Footnote 391:
C. T. R. Wilson, _Proc. Camb. Phil. Soc._ 11, p. 428, 1902; 12, p. 17, 1903.
Footnote 392:
C. T. R. Wilson, _Proc. Camb. Phil. Soc._ 12, p. 85, 1903.
Footnote 393:
Allan, _Phys. Rev._ 16, p. 106, 1903.
Footnote 394:
McLennan, _Phys. Rev._ 16, p. 184, 1903.
Footnote 395:
Schmauss, _Annal. d. Phys._ 9, p. 224, 1902.
Footnote 396:
Elster and Geitel, _Phys. Zeit_. 3, p. 574, 1902.
Footnote 397:
Ebert and Ewers, _Phys. Zeit._ 4, p. 162, 1902.
Footnote 398:
Sarasin, Tommasina and Micheli, _C. R._ 139, p. 917, 1905.
Footnote 399:
J. J. Thomson, _Phil. Mag._ Sept. 1902.
Footnote 400:
Ebert, _Sitz. Akad. d. Wiss. Munich_, 33, p. 133, 1903.
Footnote 401:
J. J. Thomson, _Phil. Mag._ Sept. 1902.
Footnote 402:
Adams, _Phil. Mag._ Nov. 1903.
Footnote 403:
Bumstead and Wheeler, _Amer. Journ. Science_, 17, p. 97, Feb. 1904.
Footnote 404:
Bumstead, _Amer. Journ. Science_, 18, July, 1904.
Footnote 405:
Dadourian, _Amer. Journ. Science_, 19, Jan. 1905.
Footnote 406:
H. S. Allen and Lord Blythswood, _Nature_, 68, p. 343, 1903; 69, p. 247, 1904.
Footnote 407:
Strutt, _Proc. Roy. Soc._ 73, p. 191, 1904.
Footnote 408:
Himstedt, _Ann. d. Phys._ 13, p. 573, 1904.
Footnote 409:
Elster and Geitel, _Phys. Zeit._ 5, No. 12, p. 321, 1904.
Footnote 410:
Dorn, _Abhandl. d. Natur. Ges. Halle_, 25, p. 107, 1904.
Footnote 411:
Schenck, Thesis Univ. Halle, 1904.
Footnote 412:
Mache, _Wien. Ber._ 113, p. 1329, 1904.
Footnote 413:
Curie and Laborde, _C. R._ 138, p. 1150, 1904.
Footnote 414:
Blanc, _Phil. Mag._ Jan. 1905.
Footnote 415:
Boltwood, _Amer. Journ. Science_, 18, Nov. 1904.
Footnote 416:
Elster and Geitel, _Phys. Zeit._ 4, p. 522, 1903.
Footnote 417:
Elster and Geitel, _Phys. Zeit._ 5, No. 1, p. 11, 1903.
Footnote 418:
Vincenti and Levi Da Zara, _Atti d. R. Instit. Veneto d. Scienze_, 54, p. 95, 1905.
Footnote 419:
Burton, _Phil. Mag._ Oct. 1904.
Footnote 420:
Elster and Geitel, _Phys. Zeit._ 6, No. 3, p. 67, 1905.
Footnote 421:
Rutherford and Allan, _Phil. Mag._ Dec. 1902.
Footnote 422:
Elster and Geitel, _Phys. Zeit._ 4, p. 138, 1902; 4, p. 522, 1903.
Footnote 423:
Saake, _Phys. Zeit._ 4, p. 626, 1903.
Footnote 424:
Simpson, _Proc. Roy. Soc._ 73, p. 209, 1904.
Footnote 425:
McLennan, _Phys. Rev._ 16, p. 184, 1903, and _Phil. Mag._ 5, p. 419, 1903.
Footnote 426:
McLennan, _Phys. Rev._ No. 4, 1903.
Footnote 427:
Rutherford and Cooke, _Americ. Phys. Soc._ Dec. 1902.
Footnote 428:
Cooke, _Phil. Mag._ Oct. 1903.
Footnote 429:
Allan, _Phil. Mag._ Feb. 1904.
Footnote 430:
Ebert, _Phys. Zeit._ 2, p. 622, 1901. _Zeitschr. f. Luftschiffahrt_, 4, Oct. 1902.
Footnote 431:
Schuster, _Proc. Manchester Phil. Soc._ p. 488, No. 12, 1904.
Footnote 432:
Mache and Von Schweidler, _Phys. Zeit._ 6, No. 3, p. 71, 1905.
Footnote 433:
Langevin, _C. R._ 140, p. 232, 1905.
Footnote 434:
Schuster, British Assoc. 1903.
Footnote 435:
J. J. Thomson, _Conduction of Electricity through Gases_, p. 324, 1903.
Footnote 436:
Miss Gates, _Phys. Rev._ 17, p. 499, 1903.
Footnote 437:
Villard, _Société de Physique_, July, 1900.
Footnote 438:
Geitel, _Phys. Zeit._ 2, p. 116, 1900.
Footnote 439:
C. T. R. Wilson, _Proc. Camb. Phil. Soc._ 11, p. 52, 1900. _Proc. Roy. Soc._ 68, p. 152, 1901.
Footnote 440:
Rutherford and Allan, _Phil. Mag._ Dec. 1902.
Footnote 441:
Patterson, _Phil. Mag._ August, 1903.
Footnote 442:
Harms, _Phys. Zeit._ 4, No. 1, p. 11, 1902.
Footnote 443:
Cooke, _Phil. Mag._ Oct. 1903.
Footnote 444:
Wilson, _Proc. Roy. Soc._ 69, p. 277, 1901.
Footnote 445:
Jaffé, _Phil. Mag._ Oct. 1904.
Footnote 446:
Patterson, _Phil. Mag._ Aug. 1903.
Footnote 447:
Strutt, _Phil. Mag._ June, 1903. _Nature_, Feb. 19, 1903.
Footnote 448:
McLennan and Burton, _Phys. Rev._ No. 4, 1903. J. J. Thomson, _Nature_, Feb. 26, 1903.
Footnote 449:
Cooke, _Phil. Mag._ Aug. 6, 1903. Rutherford, _Nature_, April 2, 1903.
Footnote 450:
Eve, _Nature_, March 16, 1905.
Footnote 451:
See article in _Le Radium_, No. 3, p. 81, Sept. 15, 1904.
Footnote 452:
J. J. Thomson, _Proc. Camb. Phil. Soc._ 12, p. 391, 1904.
Footnote 453:
Wood, _Phil. Mag._ April, 1905.
Footnote 454:
Campbell, _Nature_, p. 511, March 31, 1904. _Phil. Mag._ April, 1905.
APPENDIX A. PROPERTIES OF THE α RAYS.
A brief account is given here of some investigations made by the writer on the properties of the α rays from radium—investigations which were not completed in time for the results to be incorporated in the text.
The experiments were undertaken primarily with a view of determining accurately the value of _e_/_m_ of the α particle from radium, in order to settle definitely whether or not it is an atom of helium. In the previous experiments of the writer, Becquerel, and Des Coudres, on this subject (sections 89, 90, and 91), a thick layer of radium in radio-active equilibrium has been used as a source of α rays. Bragg (section 103) has shown that the rays emitted from radium under such conditions are complex, and consist of particles projected over a considerable range of velocity. In order to obtain a homogeneous pencil of rays it is necessary to use a very thin layer of a simple radio-active substance as a source of rays. In the experiments that follow, this condition was fulfilled by using a fine wire which was made active by exposure for several hours in the presence of a large quantity of radium emanation. By charging the wire negatively the active deposit was concentrated upon the wire, which was made intensely active. The active deposit initially contains radium A, B, and C. The activity of radium A practically disappears in about fifteen minutes, and the α radiation is then due entirely to the single product radium C, since radium B is a rayless product. The activity of radium C decreases to about 15 per cent. of its initial value after two hours.
=Magnetic deflection of the α rays.= The photographic method was employed to determine the deviation of the pencil of rays in a magnetic field. The experimental arrangement is shown in Fig. 106. The rays from the active wire, which was placed in a slot, passed through a narrow slit and fell normally on a photographic plate, placed at a known distance above the slit. The apparatus was enclosed in a brass tube which could be exhausted rapidly to a low pressure by means of a Fleuss pump. The apparatus was placed in a strong uniform magnetic field parallel to the plane of the slit. The magnetic field was reversed every ten minutes, so that on developing the plate two narrow bands were observed, the distance between which represented twice the deviation from the normal of the pencil of rays by the magnetic field. The width of the band was found to be the same whether the magnetic field was applied or not, showing that the pencil of rays was homogeneous and consisted of α particles projected with the same velocity.
By placing the photographic plate at different distances from the slit it was found that the rays, after entering the magnetic field, described the arc of a circle of radius ρ equal to 42·0 cms. The strength of field _H_ was 9470 C.G.S. units, so that the value of _H_ρ for the α particles expelled from radium C is 398,000. This is in good agreement with the maximum values of _H_ρ, previously found for radium rays (see section 92).
The electric deviation of the rays from radium C has not yet been accurately measured, but an approximate determination of _e_/_m_ for the α particles can be obtained by assuming that the heating effect of radium C is a measure of the kinetic energy of the α particles expelled from it. We have seen in section 246 that the heating effect of the radium C present in one gram of radium in radio-active equilibrium is 31 gram calories per hour, which corresponds to an emission of energy of 3·6 × 10⁵ ergs per second. Now when radio-active equilibrium is reached, the number of α particles expelled from radium C per second is equal to the number of α particles expelled per second from radium at its minimum activity. This number, _n_, is 6·2 × 10¹⁰ (section 93).
Then ½ _mnv²_ = 3·6 × 10⁵,
or (_m_/_e_)_v²_ = 1·03 × 10¹⁶,
substituting the value of _n_, and the value of the ionic charge _e_. The value of _e_ in this case has not been assumed, since _n_ = _i_/_e_, where _i_ was the measured current due to the charge carried by the α rays.
From the magnetic deflection, it is known that
(_m_/_e_)_v_ = 3·98 × 10⁵.
From these two equations we obtain
_v_ = 2·6 × 10⁹ cms. per second. _e_/_m_ = 6·5 × 10³ electromagnetic units.
These values are in surprisingly good agreement with the previous values of the writer and Des Coudres (section 91). On account of the uncertainty attaching to the value of _n_, not much weight can be attached to the determination by this method of the constants of the α particles.
=Decrease of velocity of the α particles in passing through matter.= Some experiments were made to determine the velocity of the α particles from radium C after passing through known thicknesses of aluminium. The previous apparatus was employed, and the distance between the photographic bands was observed for successive layers of aluminium foil, each ·00031 cms. thick, placed over the active wire. The photographic plate was placed 2 cms. above the slit, and the magnetic field extended 1 cm. below the slit. The amount of deviation of the rays is inversely proportional to their velocity after traversing the aluminium screens. The impressions on the plate were clear and distinct, and about the same in all cases, showing that the rays were still homogeneous after passing through the aluminium.
A clear photographic impression was obtained for 12 layers of foil, but it was not found possible to obtain any effect through 13 layers. This result shows that the photographic action of the rays, like the ionizing action, ceases very abruptly.
The results obtained are shown in the following table. Assuming that the value of _e_/_m_ is constant, the third column gives the velocity of the α particles after traversing the aluminium. This is expressed in terms of _V₀_, the velocity of the α particle when the screens are removed.
Number of Distance Velocity layers of between of α aluminum bands on the particles foil plate
0 1·46 mms. 1·00 _V₀_
5 1·71 „ ·85 „
8 1·91 „ ·76 „
10 2·01 „ ·73 „
12 2·29 „ ·64 „
13 No photographic effect
The velocity of the α particle is thus reduced only about 36 per cent. of its initial value when it fails to produce any action on the photographic plate.
Now Bragg has shown (section 104) that the α particle produces approximately the same number of ions per cm. of path in air over its whole range. Consequently, the simplest assumption to make is that the energy of the α particle is diminished by a constant amount in traversing each layer of foil. After passing through 12 layers the kinetic energy is reduced to 41 per cent. of the maximum. Each layer of foil thus absorbs 4·9 per cent. of the maximum energy. The observed kinetic energy of the α particle after passing through successive layers of foil, and the value calculated on the above assumptions, are shown in the following table.
Number of Observed Calculated layers of energy energy aluminum foil
0 100 100
5 73 75
8 58 61
10 53 51
12 41 41
The experimental and theoretical values agree within the limits of experimental error. We may thus conclude, as a first approximation, that the same proportion of the total energy is abstracted from the α particles in passing through equal distances of the absorbing screen.
=Range of ionization and photographic action in air.= The abrupt falling off of the photographic impression after the rays had passed through 12 layers of foil suggested that it might be directly connected with the corresponding abrupt falling off of the ionization in air, so clearly brought out by Bragg. This was found to be the case. It was found experimentally that the absorption in each layer of aluminium foil was equivalent to that produced by a distance of ·54 cms. of air. Twelve layers of foil thus corresponded to 6·5 cms. of air. Now Bragg found that the α rays from radium C ionize the air for a distance 6·7 cms., and that the ionization then falls off very rapidly. We may thus conclude that the α rays cease to affect the photographic plate at the same velocity as that at which they cease to ionize the gas. This is a very important result, and, as we shall see later, suggests that the action on the photographic plate is due to an ionization of the photographic salts.
The velocity of the α particles from the different radio-active products can at once be calculated, knowing the maximum range in air of the α rays from each product. The latter have been experimentally determined by Bragg. The velocity is expressed in terms of _V₀_, the initial velocity of the α particles from radium C. The rays from radium C are projected with a greater velocity than the rays from the other products of radium.
Product Maximum Velocity range of α of α particles particles in air
Radium 3 cms. ·82 _V₀_
Emanation 3·8 or 4·4 ·87 or ·90 cms. _V₀_
Rad. A 4·4 or 3·8 ·90 or ·87 „ _V₀_
Rad. C 6·7 1·00 _V₀_ „
It is difficult to determine from the experiments whether the range 3·8 cms. belongs to the rays from the emanation or from radium A. The mean velocity of the α particles is thus ·90 _V₀_, and the maximum variation for the individual products does not vary more than 10 per cent. from the mean value.
The results of Becquerel, discussed in section 92, at once receive an explanation on the above results. The α particles, expelled from radium in radio-active equilibrium, have all ranges lying between 0 and 6·7 cms. of air. The velocity of the α particles which are able to produce a photographic impression varies between ·64 _V₀_ and _V₀_. The particles which have only a short range in air are projected with a smaller velocity than those which have a greater range. The former are in consequence more bent by a magnetic field. It is thus to be expected that the apparent curvature of the path of rays in a uniform magnetic field will be greater close to the radium than at some distance away.
=Range of phosphorescent action in air.= Some experiments were also made to see whether the action of the α rays in producing luminosity in substances like zinc sulphide, barium platinocyanide, and willemite, ceased at the same distance as the ionizing action.
A very active wire was placed on a movable plate, the distance of which from a fixed screen of phosphorescent substance could be varied. The distance at which the phosphorescent action ceased could be determined fairly accurately. Different thicknesses of aluminium foil were then placed over the active wire, and the corresponding distance at which the luminosity disappeared was measured. The results are shown graphically in Fig. 107, where the ordinates represent the distance of the phosphorescent screen from the active wire, and the abscissae the number of layers of aluminium foil, each ·00031 cms. thick.
It is seen that the curve joining the points is a straight line. 12·5 thicknesses of foil absorbed the rays to the same extent as 6·8 cms. of air, so that each thickness of aluminium corresponded in absorbing power to ·54 cms. of air. For a screen of zinc sulphide, the phosphorescent action ceased at a distance of air of 6·8 cms., showing that the photographic and phosphorescent ranges of the α rays in air were practically identical.
The experiments with barium platinocyanide and willemite were more difficult, as the β and γ rays from the active wire produced a luminosity comparable with that produced by the α rays. Fairly concordant results, however, were obtained by introducing a thin sheet of black paper between the active wire and the screen. If the luminosity was sensibly changed, it was concluded that the α rays still produced an effect, and in this way the point of cessation of phosphorescent action could be approximately determined. For example, with eight thicknesses of foil over the active wire the additional thickness of air required to cut off the phosphorescent effect of the a rays was 2·5 cms. for willemite, and 2·1 cms. for barium platinocyanide.
The corresponding distance for zinc sulphide was 2·40 cms., a value intermediate between the other two.
Since eight layers of foil are equivalent to 4·3 cms. of air, the ranges in air of phosphorescent action for zinc sulphide, barium platinocyanide, and willemite correspond to 6·7, 6·8, and 6·4 cms. respectively. The differences observed are quite likely to be due to experimental error.
=Discussion of results.= We have seen that the ionizing, phosphorescent, and photographic actions of the α rays emitted from radium C cease after traversing very nearly the same distance of air. This is a surprising result when it is remembered that the α particle, after passing through this depth of air, still possesses a velocity of at least 60 per cent. of its initial value. Taking the probable value of the initial velocity of the α particle from radium C as 2·5 × 10⁹ cms. per sec., the ionizing, phosphorescent, and photographic actions cease when the velocity of the α particle falls below 1·5 × 10⁹ cms. per second, that is, a velocity of about ¹⁄₂₀ of that of light. The particle still possesses nearly 40 per cent. of its initial energy of projection at this stage.
These results show that the property of the α rays of producing ionization in gases, of producing luminosity in some substances, and of affecting a photographic plate, ceases when the velocity of the α particle falls below a certain fixed value which is the same in each case. It seems reasonable, therefore, to suppose that these three properties of the α rays must be ascribed to a common cause. Now the absorption of the α rays in gases is mainly a consequence of the energy absorbed in the production of ions in the gas. When the α particles are completely absorbed in the gas, the same total amount of ionization is produced, showing that the energy required to produce an ion is the same for all gases. On the other hand, for a constant source of radiation, the ionization per unit volume of the gas is approximately proportional to its density. Since the absorption of the α rays in solid matter is approximately proportional to the density of the absorbing medium compared with air, it is probable that this absorption is also a result of the energy used up in producing ions in the solid matter traversed, and that about the same amount of energy is required to produce an ion in matter whether solid, liquid, or gaseous.
It is probable, therefore, that the production of ions in the phosphorescent material and in the photographic film would cease at about the same velocity for which the α particle is unable to ionize the gas. On this view, then, the experimental results receive a simple explanation. The action of the α rays in producing photographic and phosphorescent actions is primarily a result of ionization. This ionization may possibly give rise to secondary actions which influence the effects observed.
This point of view is of interest in connection with the origin of the “scintillations” observed in zinc sulphide and other substances when exposed to the action of the α rays. This effect is ascribed by Becquerel to the cleavage of the crystals under the bombardment of the α particles. These results, however, show that we must look deeper for the explanation of this phenomenon. The effect is primarily due to the production of ions in the phosphorescent material and not to direct bombardment, for we have seen that the α particle produces no scintillations when it still possesses a large amount of kinetic energy. It seems not unlikely that the scintillations produced by the α rays must be ascribed to the recombination of the ions which are produced by the α particle in the crystalline mass. It is difficult to see how this ionization could result in a cleavage of the crystals.
This close connection of the photographic and phosphorescent actions of the α rays with their property of producing ions, raises the question whether photographic and phosphorescent actions in general may not, in the first place, be due to a production of ions in the substance.
=Ionization curve for the α rays from radium C.= Mr McClung, working in the laboratory of the writer, has recently determined the relative ionization per unit path of the α particles projected from radium C, using the method first employed by Bragg and discussed in section 104. An active wire, exposed for several hours to the emanation from radium, was used as a source of rays. The α particles were homogeneous, since the film of radio-active matter was extremely thin.
The relation between the ionization observed over the cross section of the narrow cone of rays and the distance from the source of rays is shown in Fig. 108.
The curve exhibits the same peculiarities as those given by Bragg for a thin film of matter of one kind. The ionization of the α particle per unit path increases slowly for about 4 cms. There is then a more rapid increase just before the α particle ceases to ionize the gas, and then a rapid falling off. The ionization does not appear to end so abruptly as is really the case, since there is a correction to be applied for the angle subtended by the cone of rays. The maximum range of the α rays in air was 6·7 cms., a number in agreement with that obtained by Bragg by measurements on the range of the rays from radium.
These results show that the ionization per unit path of the α particle increases at first slowly and then rapidly with decrease of velocity until the rays cease to ionize the gas.
=Energy required to produce an ion.= From the above results the energy required to produce an ion by collision of the α particle with the gas molecules can readily be deduced. The α particles, emitted from radium itself, are initially projected with a velocity ·88_V₀_ where _V₀_ is the initial velocity of projection of the α particles from radium C. The α particles cease to ionize the gas at a velocity ·64_V₀_. From this it can at once be deduced that ·48 of the total energy of the α particle, shot out by radium itself, is absorbed when it ceases to ionize the gas. Assuming that the heating effect of radium at its minimum activity—25 gram calories per hour per gram—is a measure of the kinetic energy of the expelled α particles, it can be calculated that the kinetic energy of each α particle is 4·7 × 10⁻⁶ ergs. The amount of energy absorbed when the α particle just ceases to ionize the gas is 2·3 × 10⁻⁶ ergs. Assuming that this energy is used up in ionization, and remembering that the α particle from radium itself produces 86000 ions in its path (section 252), the average energy required to produce an ion is 2·7 × 10⁻¹¹ ergs. This is equivalent to the energy acquired by an ion moving freely between two points differing in potential by 24 volts.
Townsend found that fresh ions were produced by an electron for a corresponding difference of potential of 10 volts. Stark, from other data, obtained a value 45 volts, while Langevin considers that 60 volts is an average value. The value obtained by Rutherford and McClung for ionization by X-rays was 175 volts, and is probably too high.
=Rayless changes.= We have seen that the α particles from the radio-active substances are projected with an average velocity not more than 30 per cent. greater than the minimum velocity, below which the α particles are unable to produce any ionizing, photographic, or phosphorescent action. Such a conclusion suggests that the property of the radio-active substances of emitting α particles has been detected because the α particles were projected slightly above this minimum velocity. A similar disintegration of matter may be taking place in other substances at a rate much greater than in uranium without producing much electrical effect, provided the α particles are projected below the critical velocity.
The α particle, on an average, produces about 100,000 ions in the gas before it is absorbed, so that the electrical effect observed is about 100,000 times as great as that due to the charge carried by the α particles alone.
It is not unlikely that the numerous rayless products which have been observed may undergo disintegration of a similar character to the products which obviously emit α rays. In the rayless product the α particle may be expelled with a velocity less than 1·5 × 10⁹ cms. per second and so fail to produce much electrical effect.
These considerations have an important bearing on the question whether matter in general is radio-active. The property of emitting α particles above the critical velocity may well be a property only of a special class of substances, and need not be exhibited by matter in general. At the same time the results suggest that ordinary matter may be undergoing transformation accompanied by the expulsion of α particles at a rate much greater than that shown by uranium, without producing appreciable electrical or photographic action.
APPENDIX B. RADIO-ACTIVE MINERALS.
Those natural mineral substances which possess marked radio-active properties have been found to contain either uranium or thorium, one of these elements being always present in sufficient proportion readily to permit its chemical separation and identification by the ordinary analytical methods[455].
A large number of uranium and thorium minerals are known at the present time, but they are for the most part found very sparingly, and some of them have been observed to occur only in a single locality. The chief commercial sources of uranium are uraninite, gummite, and carnotite, while thorium is obtained almost exclusively from monazite.
Rutherford and Soddy (_Phil. Mag._ 65, 561 (1903)), were the first to call attention to the important fact that the relations between the various radio-active substances and the other elements could best be determined from the study of the natural minerals in which these bodies occur, since these minerals represent mixtures of extreme antiquity, which have remained more or less undisturbed for almost countless ages. In dealing with these matters, however, it is highly important that we bring to our aid the data furnished by geology and mineralogy, from which it is often possible to determine the relative ages of the different substances with at least a rough degree of approximation. Thus, for example, if a certain mineral occurs as a primary constituent of a rock of remote geological period, it can safely be assumed that its age is greater than that of a similar or different mineral occurring in a later formation. It is, moreover, quite evident that those minerals which are obviously produced by the decomposition and alteration of the primary minerals, through the action of percolating water and other agencies acting from the surface downward, are of less antiquity than the primary minerals from which they originated. Through the application of these considerations it should, in general, be possible to arrange the various minerals roughly in the order of their probable ages.
The most familiar and widely known uranium mineral is uraninite, commonly called pitchblende, which consists essentially of uranium dioxide (UO₂), uranium trioxide (UO₃), and lead oxide (PbO), present in varying proportions. The uraninites can be distinguished as primary, namely, those which occur as a primary constituent of pegmatitic dikes and coarse granites, and secondary, when they occur in metalliferous veins associated with the sulphides of silver, lead, copper, nickel, iron, and zinc. The former varieties are quite frequently crystalline in character, contain a larger proportion of the rare earths and helium, and have a higher specific gravity than the latter, which are always massive and botryoidal.
The following are the most prominent localities in which primary uraninites occur:
1. North Carolina, U.S.A. (especially in Mitchell and Yancey counties). The uraninite is found in a coarse pegmatitic dike which is mined for the mica constituent. The associated feldspar of the dike is considerably decomposed through the action of meteoric waters and gases, and the uraninite itself is largely altered into the secondary minerals gummite and uranophane through the same agencies. Among the associated primary minerals are allanite, zircon, columbite, samarskite, fergusonite and monazite, while the secondary minerals include gummite, thorogummite, uranophane, autunite, phosphuranylite, hatchettolite, and cyrtolite. The geological period of this formation is difficult to establish with certainty, but is stated to be perhaps Archean, or possibly to correspond with the close of the Ordovician or with the Permian.
2. Connecticut, U.S.A. The best known localities are Glastonbury, where the uraninite is found in the feldspar quarries, and Branchville, where it occurs in an albitic granite. Both of these localities have furnished fine crystals. The geological period probably corresponds with the close of the Ordovician or Carboniferous eras, and is stated to be certainly Post-Cambrian and Pre-Triassic. Among the associated minerals are (primary) columbite, (secondary) torbernite and autunite.
3. Southern Norway, particularly in the neighbourhood of Moss. Here uraninite occurs in the augite-syenite and pegmatite. The varieties found are known as cleveite and bröggerite, and among the primary associated minerals are orthite, fergusonite, monazite, and thorite. The period is stated to be Post-Devonian.
4. Llano County, Texas. The variety of uraninite known as nivenite is found here in a quartzose pegmatite, associated with the primary minerals gadolinite, allanite and fergusonite, and the secondary minerals cyrtolite, yttrialite, gummite, and thorogummite.
Secondary uraninite is found at Johanngeorgenstadt, Marienberg and Schneeberg in Saxony, at Joachimsthal and Pribam in Bohemia, at Cornwall in England, and at Black Hawk, Colorado, and in the Black Hills, South Dakota, in the United States. The exact geological period of most of these secondary occurrences is somewhat uncertain, but they are undoubtedly very much later than the primary occurrences mentioned above.
As a matter of general interest the analysis of a typical primary uraninite (No. 1) and of a typical secondary uraninite (No. 2) is given below[456]:
No. 1 No. 2 Glastonbury, Johanngeorgenstadt, Conn. Saxony
Sp. Gr. 9·59 6·89
UO₃ 26·48 60·05
UO₂ 57·43 22·33
ThO₂ 9·79 ...
CeO₂ 0·25 ...
La₂O 0·13 ...
Y₂O₃ 0·20 ...
PbO 3·26 6·39
CaO 0·08 1·00
He und. und.
H₂O 0·61 3·17
Fe₂O₃ 0·40 0·21
SiO₂ 0·25 0·50
Al₂O₃ ... 0·20
Bi₂O₃ ... 0·75
CuO ... 0·17
MnO ... 0·09
MgO ... 0·17
Na₂O ... 0·31
P₂O₅ ... 0·06
SO₃ ... 0·19
As₂O₃ ... 2·34
Insoluble 0·70 ...
The following list comprises the more important radio-active minerals, with their approximate chemical composition and some notes on their occurrence and probable origin.
Name Composition Remarks
Uraninite, Oxides of Occurs primary Cleveite, uranium and as a Bröggerite, lead. Usually constituent of Nivenite, contains rocks and Pitchblende thorium, secondary in other rare veins with earths and metalliferous helium. sulphides Uranium 50-80%. Thorium 0-10%
Gummite (Pb, Ca) An alteration U₃SiO₁₂ product of . 6H₂O? uraninite. Uranium Formed by the 50-65% action of percolating waters
Uranophane, CaO . 2UO₃ An alteration Uranotil . 2SiO₂ . product of 6H₂O uraninite Uranium through 44-56% gummite
Carnotite A vanadate of Occurs as a uranium and secondary potassium. mineral Uranium impregnating a 42-51% porous, sedimentary sandstone. Found in Colorado and Utah
Uranosphaerite Bi₂O₃ . Alteration 2UO₃ . product of 3H₂O. other uranium Uranium 41% minerals
Torbernite, CuO . 2UO₃ „ „ Cuprouranite . P₂O₅ . 8H₂O. Uranium 44-51%
Autunite, CaO . 2UO₃ „ „ Calciouranite . P₂O₅ . 8H₂O. Uranium 45-51%
Uranocircite BaO . 2UO₃ „ „ . P₂O₅ . 8H₂O. Uranium 46%
Phosphuranylite 3UO₃ . „ „ P₂O₅ . 6H₂O. Uranium 58-64%
Zunerite CuO . 2UO₃ „ „ . As₂O₅ . 8H₂O. Uranium 46%
Uranospinite CaO . 2UO₃ „ „ . As₂O₅ . 8H₂O. Uranium 49%
Walpurgite 5Bi₂O₃ „ „ . 3UO₃ . As₂O₅ . 12H₂O. Uranium 16%
Thorogummite UO₃ . A variety of 3ThO₂ . gummite 3SiO₂ . 6H₂O? Uranium 41%
Thorite, ThSiO₄. A primary Orangite, Uranium constituent of Uranothorite 1-10%. pegmatite Thorium oxide dikes 48-71%
Thorianite Oxide of Occurs as a thorium, primary uranium, the constituent of rare earths a pegmatite and lead. dike in Contains a Ceylon. relatively Geological age large probably proportion of Archean helium. Uranium 9-10%. Thorium oxide 73-77%
Samarskite Niobate and Primary tantalate of constituent of rare earths. pegmatite Uranium 8-10% dikes
Fergusonite Metaniobate „ „ and tantalate of rare earths. Uranium 1-6%
Euxenite Niobate and „ „ titanate of rare earths. Uranium 3-10%
Monazite Phosphate of „ „ the rare earths, chiefly cerium. Uranium 0·3-0·4%
Footnote 455:
An apparent exception has been observed by Danne in the case of certain lead minerals which occur under peculiar conditions at d’Issy-l’Évêque, France. See p. 465.
Footnote 456:
Hillebrand, _Am. J. Sci._ 40, 384 (1890); _ibid._ 42, 390 (1891).
INDEX.
_The numbers refer to the pages._
α rays discovery of, 141 nature of, 141 magnetic deviation of, 142 _et seq._ electrostatic deviation of, 146 velocity of, 148 value of _e_/_m_ for, 148 charge carried by, 151 _et seq._ number of α particles expelled from one gram of radium, 155 mass and energy of, 156 origin of, in atomic disintegration, 157 scintillations produced by, 158 _et seq._ absorption of, by matter, 161 _et seq._ increase of absorption with thickness of matter traversed, 163 relative absorption of α rays from radio-elements, 164 absorption of, by gases, 165 _et seq._ connection between absorption and density, 169 relation between ionization and absorption, 170 theory of absorption of, 170 _et seq._ range of ionization of, 172 _et seq._ complexity of α rays from radium, 174 _et seq._ effect of thickness of layer of radiating matter on emission of, 195 relative ionization produced by α and β rays, 196 _et seq._ phosphorescence by α rays, 202 _et seq._ connection of, with radio-active changes, 235, 444 _et seq._, 455 from the emanations, 263 emission of energy from radio-elements in form of α rays, 419 _et seq._ connection of heat emission of radium with α rays, 421 _et seq._ number of ions produced by an α particle, 433 absence of, in rayless changes, 454 emission from active products, 454 _et seq._ loss of weight due to expulsion of, 473 α particles consist of helium, 479 _et seq._ magnetic deflection of, from radium C, 543 velocity and _e_/_m_ for, from radium C, 543 _et seq._ diminution of velocity of, in passing through matter, 545 diminution in velocity of, in passing through aluminium, 545 velocity of, when ionization ceases, 545 _et seq._ connection of phosphorescent, photographic, and ionization effects produced by, 546 _et seq._ energy required to produce an ion by α rays, 551
Abraham apparent mass of moving charged body, 71, 127
Absorption law of, in gases, 64 _et seq._ relative absorption of α, β and γ rays by matter, 111 connection between absorption and ionization, 134 _et seq._, 170 _et seq._ of β rays by solids, 134 _et seq._ connection between absorption and density for β rays, 137 of β rays in radio-active matter, 140 of α rays by solids, 161 _et seq._ of α rays in gases, 167, 170 _et seq._ connection between absorption and density for α rays, 169 theory of, 170 _et seq._ of γ rays by solids, 179 _et seq._ connection between absorption and density for γ rays, 181 of rays from the emanations, 263 of penetrating rays from the earth, 520, 540
Actinium methods of separation of, 20 _et seq._ properties of, 21 similarity to “emanating substance” of Giesel, 21 possible connection with radio-activity of thorium, 28 emanation from, 249 excited activity produced by, 311 effect of magnetic field on excited activity from, 324 separation of actinium X, 365 decay of actinium X, 365 source of actinium emanation, 365 analysis of active deposit of, 366 radiations from products of, 368 penetrating power of β and γ rays from, 368 products of, 369 table of products of, 449 possible origin of, 464
Actinium A separation and period of, 367 _et seq._
Actinium B period of, 368 properties of, 368
Actinium X separation and decay of, 364 _et seq._ production of emanation by, 365
Adams decay of activity of emanation from well water, 511 decay of excited activity from the emanation, 511
Age of radium, 457 of sun and earth, 492 _et seq._
Allan, S. J. increase with time of excited activity from atmosphere, 505 radio-activity of snow, 506 effect of conditions on decay of activity from air, 519, 523
Allan and Rutherford decay of excited activity from the atmosphere, 503 ionization of air in closed vessels, 534
Allen, H. S. and Lord Blythswood radium emanation in Bath springs, 513
Anderson and Hardy action of radium rays on the eye, 217
Armstrong and Lowry radio-activity and phosphorescence, 444
Arnold rays from phosphorescent substances, 4
Aschkinass and Caspari action of radium rays on microbes, 216
Atmosphere excited activity from, 501 _et seq._ radio-activity of, due to emanations, 504 diffusion of emanations into, from the earth, 507 effect of temperature, pressure, &c. on radio-activity of, 517 _et seq._ presence of very penetrating radiation in, 520 comparison of radio-activity of, with radio-elements, 521 _et seq._ amount of radium emanation in, 524 _et seq._ ionization of, due to radium emanation, 526
Atom number of per c.c., 54 disintegration of, 234 _et seq._ complex nature of, 235 changing atoms, 444 _et seq._ possible causes of disintegration of, 486 evolution of, 496
Atomic weight of radium by chemical methods, 17 from spectroscopic evidence, 18 emanations, 273 of radio-elements and connection with radio-activity, 445
β rays discovery of, 113 magnetic deflection of, 114 complexity of, 116 examination by the electrical method, 118 effect of, on a fluorescent screen, 119 charge carried by the, 120 _et seq._ electrostatic deviation of, 124 velocity of, and value of _e_/_m_ for, 126 variation of _e_/_m_ with velocity of, 127 _et seq._ distribution of velocity amongst β particles, 131 absorption of, 134 _et seq._ variation of absorption with density, 136 _et seq._ number of β particles stopped by matter, 137 _et seq._ variation of intensity of, with thickness of layer, 140 secondary β rays, 189 _et seq._ relative ionization produced by α and β rays, 196 relative energy emitted in form of α and β rays, 196 _et seq._ phosphorescent action of, 201 _et seq._ physical action produced by, 207 _et seq._ chemical action of, 213 physiological action of, 216 from Ur X, 347 from active deposit of radium, 377 _et seq._ significance of appearance of, only in last radio-active changes, 455 change of weight due to expulsion of, 473
Barium platinocyanide phosphorescence of, under radium rays, 203 change of colour due to radium rays, 205
Barkla polarization of X rays, 80
Barnes and Rutherford heating effect of radium emanation, 421, 429 connection of heating effect with radio-activity, 421 heating effect of active deposit, 425 heating effect of γ rays, 429 heating effect of emanation, 431 division of heating effect among active products, 433
Bary phosphorescence under radium rays, 202
Baskerville activity of thorium, 29 phosphorescence of kunzite under radium rays, 203
Baskerville and Kunz phosphorescence of substances under radium rays, 204
Beattie, Smolan and Kelvin discharging power of uranium rays, 7
Becquerel rays from calcium sulphide, 4 rays from uranium, 5 _et seq._ permanence of uranium rays, 6 discharging power of uranium rays, 6 magnetic deflection of radium rays by photographic method, 114 _et seq._ curvature of radium rays in a magnetic field, 115 _et seq._ complexity of radium rays, 116 _et seq._ electrostatic deflection of β rays of radium, 124 _et seq._ value of _e_/_m_ for β rays of radium, 126 _et seq._ magnetic deviation of α rays of radium and polonium, 145 trajectory of rays of radium in magnetic field, 148 scintillations due to cleavage of crystals, 160 γ rays from radium, 179 secondary rays produced by active substances, 187 phosphorescence produced by radium rays, 201 conductivity of paraffin under radium radiation, 210 effect of temperature on uranium rays, 210 chemical action of radium rays, 214 removal of activity from uranium by precipitation with barium, 219 theory of radio-activity, 438
Bemont et M. et Mme Curie discovery of radium, 13
Berndt spectrum of polonium, 23
Blanc thorium in sediments from hot springs, 514
Blythswood, Lord and Allen, H. S. radium emanation in Bath springs, 513
Bödlander and Runge evolution of gases from radium, 215
Boltwood origin of radium, 460 amount of radium in minerals, 460 proportionality of uranium and radium in minerals, 461 production of lead by uranium, 484 radium emanation in spring water, 514 method of standardization of amount of emanation in waters, 514
Boys rate of dissipation of charge, 531
Bragg and Kleeman theory of absorption of α rays, 172 _et seq._ relation between ionization and absorption, 174 _et seq._ range of α rays in air, 174 four sets of α rays from radium, 174 _et seq._
Bronson use of steady deflection method with an electrometer, 104 decay of thorium emanation, 242 decay of excited activity from actinium, 312
Brooks, Miss variation of excited activity from thorium for short exposures, 304 effect of dust on distribution of excited activity, 305 decay curves of excited activity of radium measured by α and β rays, 307 _et seq._ decay curves of excited activity from actinium, 312
Brooks and Rutherford absorption of α rays by matter, 161 comparison of absorption of α rays from radio-elements, 164 diffusion of radium emanation, 270 decay of excited activity from radium, 306
Bumstead presence of thorium emanation in atmosphere, 512
Bumstead and Wheeler diffusion of radium emanation, 273 emanation from surface water and the soil, 512, 522 identity of emanation from soil with radium emanation, 512, 522
Burton radium emanation in petroleum, 516
Burton and McLennan penetrating radiation from the earth, 520 radio-activity of ordinary materials, 537 emanation from ordinary matter, 538
Campbell radio-activity of ordinary materials, 540
Canal rays discovery of, 78 magnetic and electric deflection of, 78 value of _e_/_m_ for, 78 similarity of, to α rays, 110
Capacity of electroscopes, 87 of electrometers, 94, 102 standards of, 102
Carbonic acid radio-activity of natural, 516
Caspari and Aschkinass action of radium rays on microbes, 216
Cathode rays discovery of, 73 magnetic and electric deflection of, 74 value of _e_/_m_ for, 75 radiation of energy from, 79 comparison of, with β rays, 120 absorption of, by matter, 136, 137 _see also_ β rays
Caves radio-active matter present in air of, 514 _et seq._ radio-activity of air of, due to emanation from the soil, 515
Changes (_see_ Transformations)
Charge carried by the ions, 50 _et seq._ negative charge carried by β rays, 120 measurement of charge carried by β rays, 121 _et seq._ positive charge carried by α rays, 145 measurement of charge carried by α rays, 151 _et seq._
Chemical nature of emanation, 267 of active deposit, 312
Chemical actions of radium rays production of ozone, 213 coloration of glass and rock-salt, 213 on phosphorus, 214 on iodoform, 214 on globulin, 214 evolution of hydrogen and oxygen, 215
Child potential gradient between electrodes, 65 variation of current with voltage for surface ionization, 66
Clouds formation of, by condensation of water round ions, 46 _et seq._ difference between positive and negative ions in formation of, 49
Collie and Ramsay spectrum of emanation, 292
Collision ionization by, 39, 57 number of ions produced by β rays per cm. of path, 434 total number of ions produced by collisions of α particles, 434
Coloration of crystals of radiferous barium, 15 of bunsen flame by radium, 15 of glass by radium rays, 213 of rock-salt, fluor-spar and potassium sulphate by radium rays, 213
Concentration of excited activity on negative electrode, 297 activity of radium independent of, 466
Condensation of water round the ions, 46 _et seq._ of emanations, 277 experimental illustration of, 279 temperature of, 280 difference between point of, for emanations of thorium and radium, 283 from air sucked up from the earth, 510
Conductivity of gases exposed to radiations, 31 _et seq._ variation of, with pressure, 61 _et seq._ variation of, with nature of gas, 64 comparison of, for gases exposed to α, β, and γ rays, 64 comparison of, when exposed to γ rays and to hard X rays, 184 of insulators, 209 of air in caves and cellars, 507 _et seq._ of air in closed vessels, 531 _et seq._ variation of, in closed vessels with pressure and nature of gas, 534 variation of, with temperature for air in closed vessels, 536 increase of, with time, in a closed vessel, 537
Conservation of radio-activity examples of, 469 _et seq._
Cooke, H. L. penetrating rays from the earth, 520 number of ions per c.c. in closed vessels, 534 radio-activity from ordinary matter, 536
Cooke, W. T. and Ramsay radio-activity produced by radiations of radium, 472
Corpuscle (_see_ Electron)
Crookes, Sir W. spectrum of radium, 17 spectrum of polonium, 23 nature of cathode rays, 73 nature of α rays, 142 scintillations produced by radium, 158 spinthariscope, 158 number of scintillations independent of pressure and temperature, 159 phosphorescence of diamond, 204 separation of Ur X, 219 theory of radio-activity, 441
Crookes and Dewar absence of nitrogen spectrum in phosphorescent light of radium at low pressures, 206
Crystallization effect of, on activity of uranium, 349
Curie, Mme permanence of uranium rays, 6 discovery of radio-activity of thorium, 10 radio-activity of uranium and thorium minerals, 11 relative activity of compounds of uranium, 12 coloration of radium crystals, 15 spectrum of radium, 16 discovery of polonium, 22 nature of a rays, 142 absorption of α rays from polonium, 163 secondary radiation tested by electric method, 188 slowly decaying excited activity from radium, 311 recovery of activity of radium, 375 bismuth made active by solution of barium, 417
Curie, P. magnetic deviation of radium rays by electric method, 114 conductivity of dielectrics under radium rays, 209 radio-activity of radium unaffected by temperature, 210 decay of activity of radium emanation, 247 discovery of excited radio-activity from radium, 295 heat emission of radium at low temperature and variation of heat emission with age of radium, 419 nature of the emanation, 439
Curie, M. et Mme discovery of radium, 13 charge carried by β rays, 121 luminosity of radium compounds, 205 production of ozone by radium rays, 213 coloration of glass by radium rays, 213 theory of radio-activity, 439 possible absorption by radio-elements of unknown radiations, 442
Curie, J. et P. quartz piezo-électrique, 105 _et seq._
Curie, P. et Danne diffusion of radio-active emanation, 272 decay of excited activity from radium, 309 decay curves of radium and equation, 309 occlusion of radium emanation in solids, 310 changes in radium, 381 effect of temperature on active deposit, 390
Curie, P. and Debierne evolution of gas from radium, 215 active gases evolved from radium, 251 phosphorescence produced by radium emanation, 252 distribution of luminosity, 252 rate of production of emanation independent of pressure, 266 effect of pressure on amount of excited activity, 266, 317
Curie and Dewar production of helium by radium, 479
Curie, P. and Laborde heat emission of radium, 419 origin of heat from radium, 440 radium emanation in waters of hot springs, 514
Current through gases, 31 _et seq._ variation of, with distance between the plates, 59 _et seq._ variation of, with pressure of gas, 61 _et seq._ variation of, with nature of gas, 64 measurement of, by galvanometer, 84 measurement of, by electroscope, 85 _et seq._ measurement of, by electrometer, 90 _et seq._ measurement of, by quartz piezo-électrique, 105
Dadourian presence of thorium emanation in the earth, 512
Danne on deposit of radium not containing uranium, 465
Danne et Curie diffusion of radio-active emanation, 272 decay of excited activity from radium, 309 decay curves of radium and equation, 309 occlusion of radium emanation in solids, 310 changes in radium, 381 effect of temperature on active deposit, 390
Danysz action of radium rays on skin, 216
Darwin, G. H. age of sun, 492
Debierne actinium, 21 emanation from actinium, 249 decay of excited activity from actinium, 311 effect of magnetic field on activity excited from actinium, 324 barium made active by actinium, 417
Debierne and Curie evolution of gas from radium, 215 active gases evolved from radium, 251 phosphorescence produced by radium emanation, 252 distribution of luminosity, 252 rate of production of emanation independent of pressure, 266 effect of pressure on amount of excited activity, 266, 317
Decay of activity of Th X, 221 of activity of Ur X, 223 significance of law of, 229 effect of conditions on the rate of, 232 of activity of thorium emanation, 241 of activity of radium emanation, 247 of activity of actinium emanation, 249 of excited activity due to thorium for long exposure, 302 of excited activity due to thorium for short exposure, 304 of excited activity due to radium, 306 _et seq._ excited activity of slow decay due to radium, 311 of excited activity from actinium, 311 of radium A, B and C, 377 _et seq._ of radium D, E and F, 397 _et seq._ of heating effect of emanation, 423 of excited activity from atmosphere, 502 of activity of rain and snow, 506 of emanation from the earth, 508 differences in, of excited activity from atmosphere, 521 _et seq._
Demarçay spectrum of radium, 16
Deposit, active connection of, with excited activity, 301 physical and chemical properties of, 312 electrolysis of, 313 effect of temperature on, 315 effect of pressure on distribution of, 317 transmission of, by positive carriers, 318 _et seq._ nomenclature of, 328 theory of changes in, 331 _et seq._ theory of activity due to, 337 _et seq._ theory of rayless change in, 341 _et seq._ of thorium, 302 _et seq._, 351 _et seq._ analysis of, 351 rayless change in, 352 effect of temperature on, 354 period of products of, 355 of actinium, 311 _et seq._ decay curves of, 311 analysis of, 367 rayless change in, 367 period of products of, 368 radiations from, 368 of radium, 376 _et seq._ connection of excited activity with, 306 general analysis of, 376 _et seq._ analysis of, of rapid change, 377 _et seq._ analysis of α ray curves, 377 α ray curves of, 378 β ray curves of, 379 analysis of β ray curves, 381 equations of activity curves, 389 effect of temperature on, 390 volatility of, 391 of slow transformation, 311, 397 variation of α ray activity of, 398 variation of β ray activity of, 399 separation of constituents of, 401 _et seq._ successive products in, 402 variation of activity of, for long periods, 407 presence in old radium, 408 effect of, on variation of activity of radium with time, 409 presence in pitchblende, 410 connection with radio-tellurium, 411 connection with polonium, 411, 412 connection with radio-lead, 413 connection of, with radio-active induction, 415 _et seq._ heat emission of, 425 _et seq._ use of, to determine number of β particles from radium, 435 use of, as source of α rays, 543
Des Coudres magnetic and electric deviation of α rays, 148 determination of _e_/_m_ for α rays, 148
Dewar emission of heat from radium in liquid hydrogen, 420
Dewar and Crookes absence of nitrogen spectrum in phosphorescent light of radium at low pressures, 206
Dewar and Curie production of helium by radium, 479
Dielectrics condition of, under radium rays, 209
Diffusion of ions, 51 _et seq._ of radium emanation into gases, 270 of thorium emanation into gases, 275 of radium emanation into liquids, 276
Discharge action of rays on spark and electrodeless, 208
Disintegration account of theory of, 234, 325, 445 list of products of, 449 rate of, in radio-elements, 457 emission of energy in consequence of, 474 _et seq._ helium a product of, 476 _et seq._ possible causes of, 486 _et seq._ of matter in general, 496 _et seq._
Dissipation of charge in caves and cellars, 514 _et seq._ in closed vessels, 531 effect of pressure and nature of gas on, 534 _et seq._ effect of material of vessel on, 536 _et seq._
Dolezalek electrometer, construction of, 94 _et seq._
Dorn charge carried by β rays, 122 electrostatic deflection of β rays from radium, 124 discovery of radium emanation, 246 effect of moisture on emanating power of thorium, 255 electrolysis of radium solution, 313 loss of weight of radium, 474 radium emanation in springs, 513
Dreyer and Salomonsen coloration of quartz by radium rays, 213
Dunston analysis of thorianite, 486
Durack ionization by collision of electrons of great velocity, 171
Dust effect of, on recombination of ions, 42 effect of, on distribution of excited activity, 305
Earth amount of radium in, 493 _et seq._ age of, 496 excited activity deposited on, 504 activity concentrated on peaks of, 504 emanation from, 507 very penetrating radiation from, 520
Ebert condensation of emanation from the earth, 510 apparatus for determining number of ions per c.c. in air, 527 velocity of ions in air, 528
Ebert and Ewers emanation from the earth, 508
Electrolysis separation of radio-tellurium by, 25 of solutions of active deposit, 313 of radium solutions, 313 of thorium solutions, 314
Electrometer description of, 90 _et seq._ use of, in measurements, 90 construction of, 91 _et seq._ Dolezalek, 94 adjustment and screening of, 95 special key for, 97 application of, to measurements of radio-activity, 97 _et seq._ measurement of current by, 100 capacity of, 101 use with steady deflection, 103 use with quartz piezo-électrique, 105
Electron definition of, 56 production of, under different conditions, 76 _et seq._ identity of β rays with electrons, 120 _et seq._ variation of apparent mass of electron with velocity, 127 _et seq._ evidence that mass of electron is electromagnetic, 129 _et seq._ diameter of, 131
Electroscope description of, used by Curie, 85 construction of, for accurate measurements, 86 use of, in measurements of minute currents, 86 of C. T. R. Wilson, 89 use of, in measuring conductivity of air in closed vessels, 531 _et seq._ use of, for determining radio-activity of ordinary matter, 537
Elster and Geitel radio-active lead, 27 effect of magnetic field on conductivity produced in air by β rays, 113 scintillations produced by active substances, 158 action of radium rays on spark, 208 photo-electric action of body, coloured by radium rays, 214 radio-active matter in earth, 494 discovery of excited activity in atmosphere, 501 emanations from the earth, 507 radio-activity of air in caves, 507 radio-activity of the soil, 515 radio-activity of fango, 516 variation of radio-activity in atmosphere with meteorological conditions, 517 effect of temperature and pressure on atmospheric radio-activity, 518
Emanation of thorium, discovery and properties of, 238 methods of measurement of, 240 decay of activity of, 241 effect of thickness of layer on amount of, 243 increase of, with time to a maximum, 245 of radium, 246 decay of activity of, 247 of actinium, properties of, 249 of radium, phosphorescence produced by, 251 rate of emission of, 254 effect of conditions on rate of emission of, 255 regeneration of emanating power, 256 continuous rate of production of, 257 source of thorium emanation, 261 source of radium and actinium emanation, 263 radiations from, 263 effect of pressure on production of, 265 chemical nature of, 267 experiments to illustrate gaseous nature of, 268 rate of diffusion of radium emanation, 269 rate of diffusion of thorium emanation, 275 diffusion of, into liquids, 276 condensation of, 277 temperature of condensation of, 280 volume of, from one gram of radium and thorium, 288 measurement of volume of, from radium, 289 diminution of volume of, 290 spectrum of emanation, 292 connection between emanation and excited activity, 298 effect of removal of, on activity of radium, 371 _et seq._ fraction of activity of radium due to, 374 effect of rate of escape of, on activity of radium, 374 heat emission of, 420, 431 variation of heat emission with time, 421 _et seq._ enormous emission of energy from emanation, 431 radio-activity of atmosphere due to emanations, 504 sucked up from the earth, 507 in caves, 507 _et seq._ rate of decay of activity of, from the earth, 508 condensation of, from the atmosphere, 510 in well water and springs, 510 _et seq._ from “fango,” 516 effect of meteorological conditions on amount of, in atmosphere, 517 _et seq._ from metals, 538
Emanating power measurement of, 254 effect of conditions on, 255 regeneration of, 256
Emanium or “emanating substance” of Giesel (_see_ Actinium) discovery of, 21 separation and properties of, 21 similarity of, to actinium, 21 emanation from, 249 excited activity produced by, 311 action of an electric field on, 323
Energy of α particle, 156 of β particle, 196 comparison of, for α and β particles, 196 emitted from radium in form of heat, 419 _et seq._ emission of, from the emanation, 431 emission of, from radio-active products of radium, 433 total emission of, from 1 gram of radio-elements, 474 _et seq._ latent store of, in matter, 475
Eve conductivity of gases exposed to X rays, 64 conductivity of gases exposed to X rays and γ rays, 183, 184 secondary rays produced by β and γ rays, 189 _et seq._ magnetic deflection of secondary rays from γ rays, 193 variation of activity of radium with concentration, 467 amount of radium emanation in the atmosphere, 524 _et seq._ ionization due to emanation in atmosphere, 526 _et seq._
Evolution of matter evidence of, 497
Ewers and Ebert emanation from the earth, 508
Excited radio-activity discovery and properties of, 295 _et seq._ concentration of, on negative electrode, 297 connection of, with the emanations, 298 removal of, by acids, 300 decay of, due to thorium, 302 decay of, for short exposure to thorium, 304 effect of dust on distribution of, 305 decay curves for different times of exposure, 306 _et seq._ decay of, from radium, 306 decay curves of, measured by α rays, 308 decay curves of, measured by β rays, 309 decay curves of, from actinium, 311 of radium, of very slow decay, 311 effect of solution on, 312 electrolysis of active solutions, 313 effect of temperature on, 315 variation with electric field, of amount of, 316 effect of pressure on distribution of, 317 transmission of, 318 from actinium and emanium, 323 heat emission due to, 425 _et seq._ from the atmosphere, 501 _et seq._ decay of, 502 due to emanation in atmosphere, 504 distribution of, on surface of the earth, 504 concentration of, on prominences of the earth, 504 of rain and snow, 506 produced by emanation from tap water, 510 effect of meteorological conditions on amount of, 517 _et seq._ amount of, at Niagara Falls, 520 rate of decay of, dependent on conditions, 522 _et seq._
Exner and Haschek spectrum of radium, 17
Eye action of radium rays on, 217
Fehrle distribution of excited activity on a plate in electric field, 318
Fluorescence produced in substances by radium rays, 18 produced in substances by radium and polonium rays, 201 _et seq._
Fog large amount of excited activity during, 518
Forch loss of weight of radium, 474
γ rays relative conductivity of gas exposed to γ and hard X rays, 64, 184 discovery of, 179 absorption of, by matter, 179 _et seq._ connection between absorption of, and density, 182 discussion of nature of rays, 182 _et seq._ secondary rays produced by γ rays, 189 measurement of radio-activity by means of, 442, 467 conservation of radio-activity measured by, 471
Gases evolved by radium, 215 presence of helium in gases from radium, 216
Gates, Miss F. effect of temperature on excited activity, 315 discharge of quinine sulphate, 530
Geitel natural conductivity of air in closed vessels, 501, 531
Geitel and Elster radio-active lead, 27 effect of magnetic field on conductivity produced by radium rays, 113 scintillations produced by active substances, 158 action of radium rays on spark, 208 photo-electric action of bodies coloured by radium rays, 214 radio-active matter in earth, 494 discovery of radio-active matter in atmosphere, 501 emanations from the earth, 507 radio-activity of air in caves, 507 radio-activity of the soil, 515 radio-activity of fango, 516 variation of radio-activity of air with meteorological conditions, 517 effect of temperature and pressure on radio-activity in atmosphere, 518
Giesel coloration of bunsen flame by radium, 15 separation of radium by crystallization of bromide, 15 emanating substance, 21 radio-active lead, 27 magnetic deviation of β rays, 113 decrease with time of luminosity of radio-active screen, 205 spectrum of phosphorescent light of emanium due to didymium, 206, 207 coloration of bodies by radium rays, 213 evolution of gases from radium, 215 action of radium rays on the eye, 217 emanation from the emanating substance, 250 luminosity produced by radium emanation, 251 decay of excited activity of emanium, 312 activity of radium dependent on age, 371 bismuth made active by radio-active solution, 417 temperature of radium bromide above air, 420
Gimingham and Rossignol decay of thorium emanation, 242
Glass coloration produced in, by radium rays, 213 phosphorescence produced in, by emanation, 252
Glew simple form of spinthariscope, and scintillations, 159
Globulin action of radium rays on, 214
Godlewski effect of crystallization on activity of uranium, 349 diffusion of uranium X, 350 separation of actinium X, 365 source of actinium emanation, 365 recovery and decay curves of actinium, 366 penetrating power of β and γ rays from actinium, 368 radiations from active products, 368
Goldstein canal rays, 78 coloration of bodies by radium rays, 213
Gonder, Hofmann, and Wölfl properties of radio-active lead, 27, 413
Grier and Rutherford magnetic deviation of β rays of thorium, 114 relative current due to α and β rays, 195 nature of rays from Ur X, 347
Hardy coagulation of globulin by radium rays, 214
Hardy and Miss Willcock coloration of iodoform solutions by radium rays, 214
Hardy and Anderson action of radium rays on the eye, 217
Harms number of ions per c.c. in closed vessel, 534
Hartmann spectrum of phosphorescent light of emanium, 206
Haschek and Exner spectrum of radium, 17
Heat rate of emission of, from radium, 419 _et seq._ emission of, from radium at low temperatures, 420 connection of heat emission with the radio-activity, 421 _et seq._ source of heat energy, 421 _et seq._ rate of emission of, after removal of the emanation, 422 _et seq._ rate of emission of, by emanation, 423, 431 variation with time of heat emission of radium, and of its emanation, 423 heating effect of the emanation, 423, 431 heating effect of active deposit, 425 proportion of heating effect due to radio-active products, 433 origin of, in radium, 442 _et seq._ total heat emission during life of radio-elements, 474 _et seq._ heating of earth by radio-active matter, 493
Heaviside apparent mass of moving charged body, 71, 127
Helium produced by radium and its emanation, 476 _et seq._ amount of, from radium, 480 origin of, 480
Helmholtz and Richarz action of ions on steam jet, 47
Hemptinne action of rays on spark and electrodeless discharge, 208
Henning resistance of radium solutions, 208 effect of voltage on amount of excited activity, 316
Henning and Kohlrausch conductivity of solutions of radium bromide, 208
Hertz electric deviation of cathode rays, 73
Heydweiler loss of weight of radium, 474
Himstedt action of radium rays on selenium, 208 radium emanation in springs of Baden, 513
Himstedt and Meyer production of helium by radium, 479
Himstedt and Nagel action of radium rays on the eye, 217
Hofmann, Gonder, and Wölfl properties of radio-active lead, 27, 413
Hofmann and Strauss radio-active lead, 27
Hofmann and Zerban connection of activity of thorium with uranium, 29
Huggins, Sir W. and Lady spectrum of phosphorescent light of radium bromide, 205
Hydrogen production of, by radium rays, 215
Induced radio-activity (_see_ Excited radio-activity)
Induction radio-active, 24 meaning and examples of, 415 _et seq._
Insulators conduction of, under radium rays, 209
Iodoform coloration produced in, by radium rays, 214
Ionization theory of, to explain conductivity of gases, 31 _et seq._ by collision, 39, 57 variation of, with pressure of gas, 61 _et seq._ variation of, with nature of gas, 64 comparison of, produced by rays, 111, 194 production of, in insulators, 209 total, produced by 1 gram of radium, 433 _et seq._ natural ionization of gases, 531 _et seq._ connection of, with phosphorescent and photographic actions, 549
Ions in explanation of conductivity of gases, 31 _et seq._ production of, by collision, 39, 57 rate of recombination of, 40 _et seq._ mobility of, 42 _et seq._ difference between mobility of positive and negative, 43 _et seq._ condensation of water around, 46 _et seq._ difference between positive and negative, 49 charge carried by, 50 diffusion of, 51 _et seq._ charge on an ion same as on hydrogen atom, 54 number of, produced per c.c., 54 size and nature of, 55 _et seq._ definition of, 56 _et seq._ velocity acquired by, between collisions, 58 energy required to produce, 58, 551 comparative number of, produced in gases, 65 disturbance of potential gradient by movement of, 65 production of, in insulators, 209 number of, produced by α particle, 433 number produced per c.c. in closed vessels, 533 _et seq._
Joly motion of radium in an electric field, 211 absorption of radium rays by atmosphere, 492 (see foot-note)
Kaufmann velocity of cathode rays, 75 variation of _e_/_m_ with velocity of electron, 127 _et seq._
Kelvin theory of radio-activity, 441 age of sun and earth, 492, 493
Kelvin, Smolan and Beattie discharging power of uranium rays, 7
Kleeman and Bragg theory of absorption of α rays, 172 _et seq._ relation between ionization and absorption, 174 _et seq._ range of α rays in air, 174 four sets of α rays from radium, 174 _et seq._
Kohlrausch conductivity of water altered by radium rays, 208
Kohlrausch and Henning conductivity of solutions of radium bromide, 208
Kunz phosphorescence of willemite and kunzite, 203
Kunz and Baskerville phosphorescence of substance under radium rays, 204
Kunzite phosphorescence of, under radium rays, 203
Laborde and Curie heat emission of radium, 419 origin of heat from radium, 440 radium emanation in waters of hot springs, 514
Langevin coefficient of recombination of ions, 41 velocity of ions, 45 _et seq._ energy required to produce an ion, 58 secondary radiation produced by X rays, 187 slow moving ions in air, 528
Larmor radiation theory, 77 radiation of energy from moving electron, 79 structure of the atom, 157
Lead, radio-active preparation of, 26 radiations from, 26
Le Bon rays from bodies exposed to sunlight, 5 discharging power of quinine sulphate, 9, 530
Lenard ionization of gases by ultra-violet light, 9 action of ions on a steam jet, 47 penetrating power of cathode rays, 73 negative charge carried by Lenard rays, 120 absorption of cathode rays proportional to density, 136, 137
Lerch, von chemical properties of active deposit of thorium, 313 electrolysis of solution of active deposit, 313 effect of temperature on excited activity, 315 temporary activity of active deposit from thorium, 415
Lockyer inorganic evolution, 499
Lodge, Sir Oliver electronic theory, 69 instability of atoms, 487
Lorentz structure of atoms, 157
Lowry and Armstrong radio-activity and phosphorescence, 444
Luminosity of radium compounds, 205 change of, in radium compounds with time, 205 spectrum of phosphorescent light from radium bromide, 206 of radium compounds unaffected by temperature, 210
Mache radium emanation in hot springs, 513
Mache and von Schweidler velocity of ions in air, 528
Makower diffusion of radium emanation, 274 diffusion of thorium emanation, 276
Marckwald preparation of radio-tellurium, 25 rate of decay of radio-tellurium, 411
Mass apparent mass of electron, 71, 127 variation of mass of electron with speed, 127 _et seq._ of α particle, 147 _et seq._
Materials radio-activity of ordinary, 528, 536 _et seq._
Matteucci rate of dissipation of charge in closed vessels, 531
McClelland absorption of γ rays, 181 secondary rays from β and γ rays from radium, 192
McClung coefficient of recombination of ions, 41 conductivity of gases exposed to X rays, 64 ionization by α rays from radium C, 550
McClung and Rutherford energy required to produce an ion, 58 variation of current with thickness of layer of uranium, 195 estimate of energy radiated from radio-elements, 418 radiation of energy from radium, 438
McLennan absorption of cathode rays, 65 radio-activity of snow, 506 excited radio-activity at Niagara Falls, 519
McLennan and Burton penetrating radiation from the earth, 520 radio-activity of ordinary materials, 537 emanation from ordinary matter, 538
Metabolon definition of, 446 table of metabolons, 449 radio-elements as metabolons, 457
Meteorological conditions effect of, on radio-activity of atmosphere, 517
Methods of measurement in radio-activity, 82 _et seq._ comparison of photographic and electrical, 83 _et seq._ description of electrical, 84 _et seq._
Meyer and Himstedt production of helium by radium, 479
Meyer and Schweidler magnetic deviation of β rays by electrical method, 113 absorption of β rays of radium by matter, 136 activity proportional to amount of uranium, 195 emanation from uranium, 348 effect of crystallization on activity of uranium, 349 rate of decay of radio-tellurium, 411
Minerals, radio-active constant ratio of radium to uranium, 459 _et seq._ list of minerals, 461 age of, 485 composition of, 554 _et seq._
Mobility of ions, 43 _et seq._
Moisture effect of, on velocity of ions, 43, 45 effect of, on emanating power, 255
Molecule number of, in 1 c.c. of hydrogen, 54
Molecular weight of radium emanation, 273 of thorium emanation, 275
Nagel and Himstedt action of radium rays on the eye, 217
Niewenglowski rays from sulphide of calcium, 4
Nomenclature of successive products, 328 _et seq._
Number of molecules per c.c. of hydrogen, 54 of ions produced in gas by active substances, 55 of β particles expelled from 1 gram of radium, 124 of α particles emitted per gram of radium, 155 of ions produced per c.c. in closed vessels, 534
Occlusion of emanation in thorium and radium, 258 of radium emanation by solids, 310
Owens saturation current affected by dust, 42 penetrating power of rays independent of compound, 164 absorption of α rays varies directly as the pressure of gas, 169 effect of air currents on conductivity produced by thorium, 238
Oxygen change into ozone, by radium rays, 213 production of, from radium solutions, 215
Ozone production of, by radium rays, 213
Paraffin objection to, as an insulator, 96 conductivity of, under radium rays, 210
Paschen distribution of velocity amongst β particles, 131 _et seq._ absence of magnetic deflection of γ rays, 183 γ rays and electrons, 185 heating effect of γ rays, 186, 429
Patterson number of ions per c.c. in closed vessel, 534 natural conductivity of air due to an easily absorbed radiation, 536 effect of temperature on natural conductivity of air, 536
Peck and Willows action of radium rays on spark, 208
Pegram electrolysis of thorium solutions, 314 temporary activity of substances separated from thorium, 415
Penetrating power comparison of, for α, β and γ rays, 111 variation in, of β rays, 134 _et seq._ variation of, with density for β rays, 137 comparison of, for α rays from radio-elements, 164 variation of, with density for α rays, 169 variation of, with density for γ rays, 182
Penetrating radiation from the earth and atmosphere, 520
Perrin charge carried by cathode rays, 73 theory of radio-activity, 437
Phosphorescence production of, by radium, 19 production of, by radium and polonium rays, 201 _et seq._ comparison of, produced by α and β rays, 202 of zinc sulphide, 202 of barium platinocyanide, 203 of willemite and kunzite, 203 produced by radium emanation in substances, 203, 252 diminution of, with time, 205 of radium compounds, 205 spectrum of phosphorescent light of radium bromide, 205 spectrum of phosphorescent light of “emanium,” 206 production of by heat (thermo-luminescence), 207 use of, to illustrate condensation of emanations, 279 connection of with ionization, 547 _et seq._
Phosphorus action of radium rays on, 214 ionization produced by, 529
Photo-electric action produced by radium rays in certain substances, 214
Photographic method, advantages and disadvantages of, 83 relative photographic action of rays, 83 connection of photographic action with ionization, 546
Physical action of radium rays on sparks, 208 on electrodeless discharge, 208 on selenium, 208 on conductivity of insulators, 209
Physiological action of radium rays production of burns, 216 effect on bacteria, 216 effect on eye, 217
Piezo-électrique of quartz description of, 105
Pitchblendes comparison of radio-activity of, 11 radio-elements separated from, 13 _et seq._ radium continually produced from, 459 constitution of, 557
Polarization of uranium rays absence of, 7
Polonium methods of separation of, 22 rays from, 23 decay of activity of, 23 discussion of nature of, 24 similarity to radio-tellurium, 26 magnetic deviation of α rays from, 146, 150 slow moving electrons, 153 increase of absorption with thickness of matter traversed, 163 connection of, with radium F, 411
Potential required to produce saturation, 32 _et seq._ fall of potential needed to produce ions at each collision, 58 gradient due to movement of ions, 65
Precht and Runge spectrum of radium, 17 atomic weight of radium, 18 heating effect of radium, 420
Pressure effect of, on velocity of ions, 46 effect of, on current through gases, 61 _et seq._ production of emanation independent of, 265 effect of, on distribution of excited activity, 317 effect of, on natural conductivity of air in closed vessels, 534
Products, radio-active list of, from radio-elements, 449 properties of, 449 amount of in radium, 452 _et seq._ radiations from, 455
Quartz piezo-électrique use of, in measurement of current, 105
Quinine sulphate discharging power of, 530 phosphorescence of, 530
Radiations emitted by uranium, 8 emitted by thorium, 10 emitted by radium, 18 emitted by actinium, 21 emitted by polonium, 23 method of measurement of, 82 _et seq._ methods of comparison of, 108 three kinds of, 109 analogy to rays from a Crookes tube, 110 relative ionizing and penetrating power of, 111 difficulties of comparative measurement of, 112 β rays, 113 α rays, 141 γ rays, 179 secondary rays, 187 comparison of ionization of α and β rays, 194 phosphorescent effect of, 201 _et seq._ physical actions of, 207 _et seq._ chemical actions of, 213 _et seq._ physiological actions of, 216 from the emanation, 263 from Ur X, 347 connection of, with heat emission, 421 _et seq._ from different active products, 455 conservation of energy of each specific type of, 469 _et seq._
Radio-lead connection of, with polonium, 411 _et seq._ connection of, with radium D, 413
Radio-tellurium rate of decay of, 411 connection of with radium F, 411
Radium discovery of, 13 separation of, 13 spectrum of, 16 atomic weight of, 17 radiations from, 18 compounds of, 19 nature of radiations from, 109 β rays from, 113 α rays from, 141 γ rays from, 179 secondary rays from, 187 production of phosphorescence by, 201 _et seq._ spectrum of phosphorescent light of, 206 physical actions of, 207 _et seq._ chemical actions of, 213 _et seq._ physiological actions of, 216 emanation from, 246 properties of emanation from, 247 _et seq._ chemical nature of emanation from, 267 diffusion of emanation from, 269 condensation of emanation from, 277 amount of emanation from, 288 volume of emanation from, 289 spectrum of emanation from, 292 excited radio-activity from, 295 _et seq._ decay of excited activity from, 306 _et seq._ difference in properties of radium and the emanation, 327 nomenclature of products, 328 theory of successive changes in, 330 alteration of activity of, by removal of emanation, 371 _et seq._ recovery of activity of, after removal of emanation, 372 effect of escape of emanation on recovery of activity of, 374 non-separable activity of, 375 period and properties of radium A, B and C, 376 _et seq._ analysis of active deposit of rapid changes of radium, 377 analysis of β ray curves, 381 _et seq._ analysis of α ray curves, 386 _et seq._ equations of activity curves, 389 effect of temperature on active deposit of, 390 relative activity due to products of, 395 active deposit of slow transformation, 397 physical and chemical properties of radium D, E and F, 398 _et seq._ effect of temperature on active deposit of slow change, 401 separation of radium F by bismuth, 402 products of, 402 _et seq._ rate of transformation of radium D, 404 _et seq._ variation of the activity of the active deposit over long periods of time, 407 amounts of radium D, E and F in old radium, 408 variation of activity of, with time, 409 products of in pitchblende, 410 origin of radio-tellurium, 411 origin of polonium, 411, 412 origin of radio-lead, 413 temporary activity of inactive matter separated from pitchblende, 415 _et seq._ heat emission of, 419 _et seq._ heat emission of emanation from, 420, 431 heating effects due to products of, 433 theories of radio-activity of, 437 _et seq._ discussion of theories of radio-activity of, 441 _et seq._ energy of radiations, not derived from external source, 442 _et seq._ theory of radio-active change, 444 _et seq._ list of active products of, 449 amount of products of, 452 rate of change of, 457 life of radium, 457 origin of, 459 _et seq._ production of, by uranium, 459 _et seq._ amount of in 1 gram of uranium, 461 amount of, in minerals, 461 radio-activity of, independent of concentration, 466 _et seq._ disappearance of, 467 life of, independent of concentration, 468 conservation of radio-activity of, 469 _et seq._ loss of weight of, 473 experiments to determine loss of weight of, 474 total emission of energy from 1 gram of, 474 _et seq._ production of helium from, 476 helium, disintegration product of, 479 _et seq._ amount of helium from, 480 possible causes of disintegration of, 486 _et seq._ amount of, to account for heat of sun, 491 possible connection of with heat of sun, 491 possible connection of with heat of earth, 493 probable amount of, in earth, 495 amount of, in atmosphere, 495, 524 presence of, in atmosphere, 521 _et seq._
Radium A decay curve of, 378 radiation from, 381 effect of, on activity curves, 386 _et seq._ connection with later changes, 392 activity supplied by, 393
Radium B absence of rays in, 381 effect of, on activity curves, 381 _et seq._ effect of temperature on, 390 volatility of, 390 absence of heating effect of, 433 nature of rayless change in, 454, 552
Radium C radiations from, 381 analysis of β ray curves of, 381 _et seq._ analysis of α ray curves of, 386 _et seq._ effect of temperature on, 390 activity supplied by, 394 _et seq._ heating effect of, 425 use of, as a source of β rays, 435 explosive nature of change in, 456 magnetic deflection of rays from, 543 velocity and value of _e_/_m_ for rays from, 544
Radium D origin of name of, 376 connection of, with active deposit, 403 period of transformation of, 406 effect of, on variation of activity, 407 presence in old radium, 408 effect of, on activity of old radium, 409 presence in pitchblende, 410 connection with radio-lead, 413 amount of, in 1 ton of uranium, 454
Radium E effect of temperature on, 401 connection of, with β ray activity active deposit, 403, 400 connection with radio-lead, 413
Radium F variation of activity due to, 398 effect of temperature on, 401 separation of, on bismuth plate, 402 connection with active deposit, 403 variation of activity of, over long periods of time, 407 presence in old radium, 409 effect of, on activity of old radium, 409 presence in pitchblende, 410 connection with radio-tellurium, 411 connection with polonium, 411, 412 connection with radio-lead, 413
Rain radio-activity of, 505 decay of activity of, 506
Ramsay, Sir W. amount of helium in thorianite, 486
Ramsay and Collie spectrum of emanation, 292
Ramsay and Cooke radio-activity produced by radiation from radium, 472
Ramsay and Soddy evolution of gas from radium, 215 production of hydrogen and oxygen from radium, 215 chemical nature of the emanation, 268 gaseous nature of the emanation, 268 volume of emanation, and change with time, 289 helium from radium emanation, 291 amount of helium produced by radium, 480
Ramsay and Travers amount of helium in fergusonite, 486
Rayless changes discussion of, 454, 552
Re, F. theory of radio-activity, 441
Recombination of ions, 40 _et seq._ constant of, 42
Recovery of activity of thorium after removal of Th X, 221 of activity of uranium after removal of Ur X, 223 significance of law of, 224 effect of conditions on rate of, 232 of activity of radium after removal of emanation, 372 of heating effect of radium, 423
Reflection no evidence of direct reflection for uranium rays, 7 diffuse reflection of rays, 7
Refraction no evidence of, for uranium rays, 7
Regeneration of emanating power, 256
Richarz and von Helmholtz action of ions on steam jet, 47
Richarz and Schenck theory of radio-activity, 441
Rossignol and Gimingham decay of thorium emanation, 242
Runge spectrum of radium, 17
Runge and Bödlander evolution of gas from radium, 215
Runge and Precht spectrum of radium, 17 atomic weight of radium, 18 heating effect of radium, 420
Russel photographic action of substances, 83
Saake amount of emanation in air at high altitudes, 519
Salomonsen and Dreyer coloration of quartz by radium rays, 213
Saturation current meaning of, 33 _et seq._ application of, to measurements of radio-activity, 84 measurement of, 100 _et seq._
Schenck radium emanation in springs, 513
Schenck and Richarz theory of radio-activity, 441
Schmidt discovery of radio-activity of thorium, 10
Schmidt and Wiedemann thermo-luminescence, 207
Schuster number of ions per c.c. in air of Manchester, 528 radio-activity of matter, 529
Schweidler and Mache velocity of ions in air, 528
Schweidler and Meyer magnetic deviation of β rays by electrical method, 113 absorption of β rays of radium by matter, 136 activity proportional to amount of uranium, 195 emanation from uranium, 348 effect of crystallization on activity of uranium, 349 rate of decay of radio-tellurium, 411
Scintillations discovery of, in zinc sulphide screen, 158 connection of, with α rays, 158 illustration of, by spinthariscope, 158 cause of, 160 production of, by action of electric field, 160
Searle apparent mass of moving charged body, 71, 127
Secondary rays examination of, by photographic method, 187 examination of, by electrical method, 188 production of, by β and γ rays, 189 _et seq._ from different materials, 191 amount of, depends upon atomic weight, 192 magnetic deflection of, 193
Seitz absorption of electrons by matter, 137 _et seq._
Selenium action of radium rays on, 208
Simon value of _e_/_m_ for cathode rays, 75, 129
Simpson amount of excited activity in north of Norway, 519
Slater, Miss effect of temperature on active deposit of thorium, 354
Smolan, Beattie and Kelvin discharging power of uranium rays, 7
Snow radio-activity of, 506 decay of activity of, 507
Soddy comparison of photographic and electrical action of uranium rays, 83 nature of rays from Ur X, 347 production of radium from uranium, 463
Soddy and Ramsay evolution of gas from radium, 215 production of hydrogen and oxygen from radium, 215 chemical nature of the emanation, 268 gaseous nature of the emanation, 268 volume of the emanation, and change with time, 289 helium from radium emanation, 291 amount of helium produced by radium, 480
Soddy and Rutherford separation of Th X, 220 decay of activity of Th X, 221 recovery of activity of thorium freed from Th X, 221 decay of activity of Ur X, 223 recovery of activity of uranium freed from Ur X, 223 explanation of decay and recovery curves, 224 rate of production of Th X, 227 theory of decay of activity, 229 influence of conditions on rate of decay and recovery of activity, 233 disintegration hypothesis, 234 decay of activity of radium emanation, 247 measurements of emanating power, 254 effect of temperature, moisture, and solution, on emanating power, 255 regeneration of emanating power, 256 constant rate of production of emanation of radium and thorium, 257 source of thorium emanation, 261 radiations from the emanation, 264 chemical nature of emanation, 267 condensation of emanations of radium and thorium, 277 temperature of condensation of emanation, 278 effect of successive precipitations on activity of thorium, 358 recovery of activity of radium, 372 theory of radio-activity, 439 theory of radio-active change, 445 conservation of radio-activity, 469
Soil radio-activity of, 507 _et seq._ difference in activity of, 508 _et seq._
Solution coloration of, by radium, 15 of active deposit in acids, 312 electrolysis of active, 313
Source of thorium emanation, 261 of radium and actinium emanations, 263
Spark action of radium rays on, 208
Spectrum spark spectrum of radium, 15, 16 flame spectrum of radium, 17 effect of a magnetic field on spectrum of radium, 17 of polonium, 23 of phosphorescent light of radium bromide, 206 of emanation, 292 of helium in radium gases and emanation, 477
Spinthariscope description of, 158
Springs emanation from water of, 513
Stark energy to produce an ion, 58
Stoney, Johnstone use of term electron, 76
Strauss and Hofmann radio-active lead, 27
Strutt conductivity of gases for radiation, 63, 64 conductivity of gases produced by γ rays, 64, 183 negative charge carried by β rays, 122 _et seq._ absorption of β rays proportional to density, 136 nature of α rays, 142 attempt to measure charge of α rays, 153 constant ratio of uranium to radium in minerals, 462 connection of thorium with helium, 483 absorption of radium rays from sun by atmosphere, 492 presence of radium in Bath waters, 513 radio-activity of ordinary matter, 536
Sun effect of radium in, 491 age of, 492
Temperature effect of, on intensity of radiations from uranium and radium, 210 effect of, on luminosity, 210 rate of decay of radium emanation unaffected by, 249 of condensation of emanations, 283 rate of decay of thorium emanation unaffected by, 287 effect of, on excited activity, 315 effect of, on active deposit of thorium, 354 effect of, on active deposit of actinium, 368 effect of, on active deposit of rapid change of radium, 390 effect of, on active deposit of slow change, 401 of radium above surrounding space, 419 effect of, on amount of excited activity in atmosphere, 518 effect of, on natural ionization of air, 536
Theories of radio-activity, review of, 437 _et seq._ discussion of, 441 _et seq._ disintegration theory, 445 _et seq._
Thermo-luminescence, 207
Thomson, J. J. relation between current and voltage for ionized gases, 34 difference between ions as condensation nuclei, 49 charge on ion, 50 magnetic field produced by an ion in motion, 69 apparent mass of electron, 71 action of magnetic field on moving ion, 72 determination of _e_/_m_ for cathode stream, 73 origin of X rays, 80 slow velocity electrons from radio-tellurium, 153 charge carried by α rays, 154 theory of radio-activity, 440 cause of heat emission from radium, 442 structure of atom, 487 possible causes of disintegration of radium, 487 nature of electrons, 496 emanation from tap-water and deep wells, 510 radio-activity of ordinary materials, 539
Thomson, J. J. and Rutherford ionization theory of gases, 31 _et seq._
Thorium discovery of radio-activity of, 10 emanation from, 11 preparation of non-radio-active thorium, 29 nature of radiations from, 109 β rays from, 114 α rays from, 141 γ rays from, 180 separation of Th X from, 220 recovery of activity of, 221 disintegration of, 234 emanation from, 238 properties of emanation from, 239 diffusion of emanation from, 275 condensation of emanation from, 277 excited radio-activity from, 295 _et seq._ analysis of active deposit of, 351 _et seq._ rayless change in, 352 explanation of initial portion of decay curve, 358 explanation of initial portion of recovery curve, 358 effect of successive precipitations on, 358 recovery curve after large number of precipitations, 359 products of, 363 non-separable activity of, 363 radiations from active products of, 363 division of activity amongst active products of, 363 rate of emission of energy by, 432 theories of radio-activity of, 438 discussion of theories of radio-activity, 441 _et seq._ source of energy of radiations, 442 _et seq._ theory of radio-active change, 444 _et seq._ table of radio-active products of, 449 rate of change of, 458 life of, 458 conservation of radio-activity of, 469 total emission of energy from 1 gram of, 475 possible causes of disintegration of, 486 _et seq._
Thorium A period and properties of, 352 _et seq._ absence of rays in, 352 effect of temperature on, 354
Thorium B period and properties of, 352 _et seq._ effect of temperature on, 354 radiations from, 363
Thorium X methods of separation of, 220 law of decay of activity of, 221 law of recovery of activity of, 221 theory to explain production of, 224 material nature of, 226 continuous production of, 227 explanation of decay of activity of, 229 effect of conditions on the rate of change of, 233 disintegration hypothesis to explain production of, 234 minute amount of, produced, 237 effect of successive separations of, on activity of thorium, 358 _et seq._ analysis of decay and recovery curves of, 358 radiations from, 363
Tommasina scintillations produced by electrification, 160
Townsend ions by collision, 39, 57 coefficient of recombination, 41 diffusion of ions, 51 _et seq._ comparison of charge on ion with that on hydrogen atom in electrolysis, 53 number of molecules per c.c. of gas, 54 ionization by collision for different speeds, 171
Transformations, successive theory of, 325 _et seq._ nomenclature of, 328 activity due to, 337 detection of a rayless change in, 341 in uranium, 346 _et seq._ in thorium, 351 _et seq._ in actinium, 364 _et seq._ in radium, 371 _et seq._ list of, 449 origin of radium in, 459 helium, a result of, 476 _et seq._ possible cause of, 486 _et seq._ application of, to evolution of matter, 497 _et seq._
Transmission of excited radio-activity of radium and thorium, 318 _et seq._ of excited radio-activity of actinium, 323
Travers and Ramsay amount of helium in fergusonite, 486
Troost rays from hexagonal blende, 4
Uranium discovery of radio-activity of, 5 persistence of radiations of, 6 discharging power of rays, 7 absence of reflection, refraction and polarization, 7 examination of uranium minerals, 11 _et seq._ relative activity of compounds of uranium, 12 nature of radiations from, 109 β rays from, 114 α rays from, 141 γ rays from, 180 separation of Ur X from, 219 recovery of activity of, 219 changes in, 346 _et seq._ non-separable activity of, 347 radiations from Ur X, 347 _et seq._ method of measurement of activity of Ur X, 347 emission of energy by, 418 theories of radio-activity of, 437 _et seq._ discussion of theories of radio-activity, 441 _et seq._ source of energy of radiation, 442 _et seq._ theory of radio-active change, 444 _et seq._ table of active products, 449 rate of change of, 458 life of, 458 radium probable product of, 459 _et seq._ amount of radium in, 460 _et seq._ amount of, in radio-active minerals, 461 growth of radium in, 463 conservation of radio-activity of, 469 total emission of energy from 1 gram of, 475 possible causes of disintegration of, 486 _et seq._
Uranium X separation of, by Crookes, 219 separation of, by Becquerel, 219 decay of activity of, 223 recovery of activity of, 223 theory to explain production of, 224 _et seq._ material nature of, 226 explanation of decay of activity of, 229 changes in, 346 _et seq._ radiations from, 347 _et seq._ method of measurement of radiations from, 347 effect of crystallization on activity of, 349 diffusion of, 350
Velocity of ions in electric field, 42 _et seq._ difference between, of positive and negative ions, 43 _et seq._ of β particle or electron, 126 _et seq._ variation of mass of electron with, 127 of α particle, 148 of transmission of carriers of excited activity, 320 _et seq._ of ions in atmosphere, 528
Villard discovery of γ rays from radium, 179 alteration of X ray screen with time, 205 activity produced by cathode rays, 530
Vincenti and Levi Da Zara radium emanation in spring waters, 516
Voller variation of activity of radium with concentration, 467
Volume of radium emanation, calculation of, 289 decrease of, of radium emanation, 290
Walker, G. W. theory of electrometer, 90
Walkhoff action of radium rays on skin, 216
Wallstabe diffusion of radium emanation into liquids, 276
Water emanation from, 510 _et seq._ decay of activity of emanation from, 511 _et seq._
Water-falls amount of excited activity produced at Niagara, 520 electrification produced near, 520
Watts, Marshall atomic weight of radium, 18
Weichert velocity of cathode rays, 76
Weight loss of by radio-elements, 473 attempts to measure loss of in radium, 474
Wheeler and Bumstead diffusion of radium emanation, 273 emanation from surface water and the soil, 512, 522 identity of emanation from soil with radium emanation, 512, 522
Whetham effect of valency of ion on colloidal solutions, 215 production of radium from uranium, 463
Wiedemann thermo-luminescence, 207
Wiedemann and Schmidt thermo-luminescence, 207
Wien value of _e_/_m_ for canal rays, 78 positive charge of canal rays, 78 amount of charge carried by β rays, 124
Willcock, Miss and Hardy coloration of iodoform solution by radium rays, 214
Willemite phosphorescence of, under radium rays, 203 use of, to show condensation of emanation, 279
Willows and Peck action of radium rays on spark, 208
Wilson, C. T. R. ions as nuclei of condensation, 47 _et seq._ difference between positive and negative ions as condensation nuclei, 49 equality of charges carried by positive and negative ions, 50 construction of electroscope, 86, 88 natural ionization of air in vessels, 501 radio-activity of rain and snow, 505, 506 loss of charge in closed vessels, 531 _et seq._, 534 presence of ions in dust-free air shown by condensation, 533 number of ions produced per c.c., 533 effect of pressure and nature of gas on ionization in sealed vessels, 534
Wilson, H. A. charge on ion, 51
Wilson, W. E. radium in sun, 491
Wölfl, Hofmann and Gonder properties of radio-active lead, 27, 413
Wood, A. radio-activity of ordinary materials, 540
Zara, Levi Da and Vincenti radium emanation in spring waters, 516
Zeeman action of magnetic field on light, 77
Zeleny velocity of ions, 42 _et seq._ difference of velocity of ions, 45 potential gradient between electrodes, 65
Zerban and Hofmann connection of activity of thorium with uranium, 29
Zinc Sulphide scintillations produced in by α rays, 158 cause of luminosity of, 160, 549
CAMBRIDGE: PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS.
CAMBRIDGE PHYSICAL SERIES.
=Conduction of Electricity through Gases.= By J. J. THOMSON, D.Sc., LL.D., Ph.D., F.R.S., Fellow of Trinity College and Cavendish Professor of Experimental Physics. Demy 8vo. viii + 568 pp. 16_s._
CONTENTS.
I. Electrical Conductivity of Gases in a normal state.
II. Properties of a Gas when in the conducting state.
III. Mathematical Theory of the Conduction of Electricity through a Gas containing Ions.
IV. Effect produced by a Magnetic Field on the Motion of the Ions.
V. Determination of the Ratio of the Charge to the Mass of an Ion.
VI. Determination of the Charge carried by the Negative Ion.
VII. On some Physical Properties of Gaseous Ions.
VIII. Ionisation by Incandescent Solids.
IX. Ionisation in Gases from Flames.
X. Ionisation by Light. Photo-Electric Effects.
XI. Ionisation by Röntgen Rays.
XII. Becquerel Rays.
XIII. Spark Discharge.
XIV. The Electric Arc.
XV. Discharge through Gases at Low Pressures.
XVI. Theory of the Discharge through Vacuum Tubes.
XVII. Cathode Rays.
XVIII. Röntgen Rays.
XIX. Properties of Moving Electrified Bodies.
Supplementary Notes.
Index.
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=A Treatise on the Theory of Solution, including the Phenomena of Electrolysis.= By WILLIAM CECIL DAMPIER WHETHAM, M.A., F.R.S., Fellow of Trinity College. Demy 8vo. x + 488 pp. 10_s._ net.
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CONTENTS OF MR WHETHAM’S ‘SOLUTION AND ELECTROLYSIS.’
I. Thermodynamics.
II. The Phase Rule.
III. The Phase Rule. Two Components. Solutions.
IV. Solubility.
V. Osmotic Pressure.
VI. Vapour Pressures and Freezing Points.
VII. Theories of Solution.
VIII. Electrolysis.
IX. Conductivity of Electrolytes.
X. Galvanic Cells.
XI. Contact Electricity and Polarization.
XII. The Theory of Electrolytic Dissociation.
XIII. Diffusion in Solutions.
XIV. Solutions of Colloids.
Additions.
Table of Electro-chemical Properties of Aqueous Solutions.
=Electricity and Magnetism=: an Elementary Text-book, Theoretical and Practical. By R. T. GLAZEBROOK, M.A., F.R.S., Director of the National Physical Laboratory and Fellow of Trinity College, Cambridge. Crown 8vo. Cloth. 1-440 pp. 7_s._ 6_d._
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PREFACE. Some words are perhaps necessary to explain the publication of another book dealing with Elementary Electricity. A considerable portion of the present work has been in type for a long time; it was used originally as a part of the practical work in Physics for Medical Students at the Cavendish Laboratory in connexion with my lectures, and was expanded by Mr Wilberforce and Mr Fitzpatrick in one of their Laboratory Note-books of Practical Physics.
When I ceased to deliver the first year course I was asked to print my lectures for the use, primarily, of the Students attending the practical classes; the lectures on Mechanics, Heat and Light have been in type for some years. Other claims on my time have prevented the issue of the present volume until now, when it appears in response to the promise made several years ago.
Meanwhile the subject has changed; but while this is the case the elementary laws and measurements on which the science is based remain unaltered, and I trust the book may be found of service to others besides my successors at the Cavendish Laboratory.
The book is to be used in the same way as its predecessors. The apparatus for most of the Experiments is of a simple character and can be supplied at no great expense in considerable quantities.
Thus the Experiments should all, as far as possible, be carried out by the members of the class, the teacher should base his reasoning on the results actually obtained by his pupils. Ten or twelve years ago this method was far from common; the importance to a School of a Physical Laboratory is now more generally recognized; it is with the hope that the book may be of value to those who are endeavouring to put the method in practice that it is issued now.
=Heat and Light.= An Elementary Text-book, Theoretical and Practical, for Colleges and Schools. By R. T. GLAZEBROOK, M.A. Crown 8vo. 5_s._
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=Heat.= 230 pp. 3_s._ =Light.= 213 pp. 3_s._
=Mechanics and Hydrostatics.= An Elementary Text-book, Theoretical and Practical, for Colleges and Schools. By R. T. GLAZEBROOK, M.A. Crown 8vo. 8_s._ 6_d._
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