ii. Other circumstances being the same, the specific heat of gases

diminishes with diminution of pressure, and equally for all the gases: the progression converges slightly and in a ratio much less than that of the pressures.

iii. Each gas has a different conducting power, _i.e._, all the gases have not the some power of communicating or receiving heat.—_Ann. de Chimie_, xxxv. 5.

2. _On the Incandescence and Light of Lime_.—The experiments made by Lieutenant Drummond upon the light of lime and other earths when highly ignited, with the highly interesting application which he has made of that emitted from lime, to the purpose of geodesical surveys, has induced M. Pleischel to repeat and vary the results. He states that the utmost light is given by lime; the earth being pulverised and exposed on burning charcoal to the heat excited by a jet of oxygen falling upon it. He endeavours to account for the effect, by supposing a kind of pulverulent atmosphere disengaged from the lime at the high temperature used, and considers that the substances which are competent to emit molecules only in the gaseous state, cannot produce this intense light.—_Zeitschrift für Physik_, &c.

3. _Evolution of Heat during the Compression of Water_. May 14, 1827.—M. Arago announced to the Academy of Sciences, that M. Despretz had ascertained experimentally, that the compression of water by a force equal to 20 atmospheres, caused the disengagement of one sixty-sixth part of a degree of heat.

4. _On Electrical Excitation_.—M. Walcker affirms positively from experiments made with great care, that three bodies of different exciting power are necessary, in every case of excitation of electricity by contact, and that all the phenomena of this kind are subject to this condition. If, for instance, two portions of the same metal being put in contact, electricity is produced, it is because there are three different states of temperature brought into play, one being the result of the other two, and a mean between them. One fact which more than any other sanctioned this idea, was, that the electric [p202] currents were the more apparent as this third state of temperature was made more sensible.—_Bull. Univ._, A. vii. 374.

5. _Magnetic Repulsion_.—A very remarkable result has been obtained by M. Becquerel, from the use of an extremely delicate magnetic arrangement, which he has for the present called a _sideroscope_. Its use is exactly the same in principle as that of the magnetic needle, indicating iron, for instance, by the attraction manifested; but it is so delicate that it will show it in the most minute quantity possible, as, for instance, in gold, silver, or copper money, innumerable minerals, &c. This instrument shows no magnetic power or attraction in gold, silver, copper, palladium, tin, lead, zinc, or brass, when chemically pure, and a great many vegetable and mineral substances have no action on it: but the most curious result is, that very pure bismuth and even that of commerce has a _repulsive_ power, which, if it be found ultimately to be independent of any magnetic _polarity_, is the first fact of the kind that has been made known. Antimony also presents the same phenomenon.

6. _Diminished Solubility of Substances by Heat_.—Mr. Graham has added one to the few facts of this kind with which we were acquainted, and has accompanied its description with some very interesting considerations, which may be found at length in the Philosophical Magazine, N. S., ii. 20. The salt experimented with by Mr. Graham is the phosphate of magnesia; which may be prepared by mixing a solution of 21 parts of phosphate of soda with one of 15.375 parts of sulphate of magnesia: within 24 hours the phosphate of magnesia precipitates in acicular crystals; they should be agitated with repeated portions of water, then thrown upon a filter with more water, and left to dry.

Solutions were obtained by occasionally agitating this salt with water in the proportion of 2 ounces to a pint of the fluid, for four days; being then decanted and filtered, they had a sweetish taste. A quantity of this fluid being heated in a water-bath, became turbid before the temperature had attained 120° F.; at 212° a cloudy precipitate slowly subsided, and the supernatant fluid became nearly transparent. The precipitate was found to be anhydrous phosphate of magnesia; and, by further experiment, the difference in solubility was found to be such, that water at 45°, dissolving 1/744th part its weight of the anhydrous salt, water at 212° only dissolved 1/1151th part. When in the state of crystals, or as hydrate, the proportions of salt were 1/322 and 1/498 to 1 of water.

Mere continuance of the heat had no effect in increasing the precipitate either of this salt, or from aqueous solution of lime, provided no part of the solution was at any time converted into vapour; but if the solution only occupied a small part of the vessel, and ebullition came on, then, although all the water might be returned to the solution, yet the precipitation went on, and might be [p203] increased _ad libitum_, particularly in the case of lime water. The cause of the precipitate appears to be the same in all these cases. The moment a drop of the solution is converted into vapour, it deposits the quantity of lime or salt which it held in solution; and in the case of bodies which dissolve so sparingly and with so much difficulty, although the water be returned again to the solution, it is incapable of re-dissolving what it has deposited. We know that it would be a hopeless task to form a saturated solution of lime by agitating with the water no more than the few grains which it is capable of dissolving; and in the case of ebullition, when the lime is once deposited, there should be the same difficulty in taking it up.

Mr. Graham states that he has observed this effect not only in lime-water and in solution of phosphate of magnesia, but to a certain extent in all bodies of difficult solubility, in the sulphate of lime, for instance, even when greatly diluted; and he believes that the deposite from slight boiling observed in many mineral waters, and generally attributed to the dissipation of carbonic acid gas, depends, in some instances, upon this cause. However weak the solution may be, it is evident that a portion of the salt may be deposited in this way.

7. _On the Composition of Cyanic Acid_.—M. Wohler some time since announced the production of cyanic acid, and cyanates, corresponding in composition to the substance presumed to exist in the fulminating compounds of silver, mercury, &c., the nature of which was made out by MM. Liebig and Gay Lussac. M. Liebig, upon repeating M. Wohler’s experiments upon his cyanate of silver, obtained only 71.012 per cent. of oxide of silver, instead of 77.23, which was the quantity present according to M. Wohler’s analysis, and concluded that the acid was the cyanous, and not the cyanic. The latter philosopher was consequently induced to repeat his experiments: one of his methods of decomposing the cyanate of silver was by muriatic acid gas: at first liquid cyanic acid forms, which is very soon transformed into a white crystalline mass; but, on continuing the operation, and applying a higher heat, a large quantity of muriate of ammonia and cyanic acid is evolved. This process indicated 77.5 per cent. of oxide of silver in the salt. Another process consisted in dissolving the cyanate in nitric acid, and precipitating the silver by muriatic acid, the result was 77.05 of oxide per cent. A third analysis, made by reducing the silver of the salt, gave a result of 77.35 per cent. oxide. The mean of these is 77.3, and the theoretical number obtained by calculation is 77.23, so that the acid appears to be truly the cyanic; and the curious fact of its being the same in composition with that in the fulminating compounds of silver and mercury, but very unlike in properties, still remains undisturbed.—_Bull. Univ._, A. viii. 53.

8. _Iodous Acid_.—According to M. Wohler, the iodous acid of [p204] M. Sementini[35] is nothing more than a mixture of chloride of iodine and iodine. When saturated with carbonate of soda, the iodine in solution is precipitated, and on evaporating the solution to dryness, and heating it strongly, the residue fuses, and by proper tests is found to be a mixture of chloride and iodide of sodium.

These statements apply only to the iodous acid: as to the oxide of iodine, no source of chlorine exists in the process last described by M. Sementini.

FOOTNOTE:

[35] See the last volume of this Journal, p. 477.

9. _On Manganesic Acid, by_ M. Unverdorben.—When manganesate of potash is distilled with a little anhydrous sulphuric acid, manganesic acid is evolved in the form of a red transparent gas, which dissolves in water, forming a red solution. The gas frequently decomposes spontaneously in the retort, with explosion, producing oxide of manganese and oxygen.

Manganesate of potash was analysed by distilling it with excess of sulphuric acid, collecting the oxygen disengaged, and estimating the proportion of protoxide of manganese and salts of potash remaining in the retort. According to these experiments the acid consists of

Manganese 58.74 Oxygen 41.26 ------ 100.00

And the manganesate of potash of Or being calcined Potash 25.63 32.75 Manganese acid 52.44 67.25 Water 21.93 ------ ------ 100.00 100.00 _Ann. des Mines_, 1827, p. 145.

10. _Heavy Muriatic Ether, and Hydrocarburet of Chlorine or Chloric Ether_.—Some comparative experiments have been made on these two substances by M. Vogel. He prepared the former of them by passing chlorine gas into alcohol. The muriatic acid was then separated by distilling the fluid from off chalk, in which operation the muriatic ether and alcohol passed over together, and these were divided by the addition of water, which dissolved the latter, and left the former. The chloric ether was made as usual from chlorine and olefiant gases. The results that were obtained by acting on these substances by a high temperature, potash, phosphorus, &c., induced M. Vogel to consider them as identical in composition, notwithstanding some differences in their physical properties; the specific gravity of the muriatic ether was 1.134, that of the chloric ether 1.214, and the odour of the latter is more aromatic, and the taste more sweet than of the former.

Whilst passing the chlorine into the alcohol, M. Vogel observed [p205] that if the sun shone upon the substances when the action was nearly complete, each bubble of chlorine as it entered the alcohol produced a bright purple flame, a dense white vapour, and caused violent concussions in the liquid; another curious instance, in addition to the many that are known, of the power of solar light over chemical action.—_Journ. de Pharm._ 1826, p. 627.

11. _Test for the Presence of Nitric Acid_.—The following method is one devised by Dr. Liebig, for the detection of this substance, which it will effect, he says, when there is not more than a four-hundredth part of the acid present. The liquid to be examined must be mixed with sufficient sulphuric solution of indigo to acquire a distinct blue colour, a few drops of sulphuric acid added, and the whole boiled. If the liquid contains a nitrate, it will be bleached, or, if the quantity is very small, rendered yellow. By adding a little muriate of soda to the liquid before applying heat, a five-hundredth of nitric acid may easily be discovered.—_Ann. de Chimie_, xxxv. 80.

12. _Peculiar Formation of Nitre_.—The leaves and stems of beet root contain oxalate and malate of potash. Some leaves were tied together and hung up in a warm and slightly-humid place, where there was but little light, to dry. Being examined at the end of several months, they were found penetrated with, and covered by, an immense number of minute crystals of nitre. The oxalic and malic acids had been replaced by nitric acid; but whether from animalized matter naturally in the leaves of the plant, or from the action of the air, or in what manner, is not known.—M. HENRI BRACONNOT, _Ann. de Chimie_, xxxv. 260.

13. _Experiments on Fluoric Acid and Fluates, by_ M. Kuhlman.—These experiments were made with dry sulphuric acid and fluor spar, with the intention of proving that fluor spar is truly a compound of fluorine and calcium, and not of fluoric acid and oxide of calcium. A quantity of anhydrous sulphuric acid was prepared with great care, and collected in a glass tube; the latter was then connected with a platina tube charged with fluor spar, which had previously been calcined in a platina crucible, and a glass tube was connected with the other end of the platina tube for the purpose of conducting and facilitating the collection of the gas evolved over mercury. The fluor spar was heated to redness, and then the temperature of the sulphuric acid raised so as to cause a stream of it in vapour to pass over the fluor spar; but there was not the slightest reaction, the sulphuric acid recondensed in part in the farthest tube, and no trace of fluoric acid was produced. Dry sulphuric acid was then put, in the liquid state, in contact with dry fluor spar, but there was no decomposition, and no portion of the spar was converted [p206] into sulphate of lime. The first experiment was then repeated, with the difference of using hydrated sulphuric acid of specific gravity 1.842, and there was instantly much fluoric acid produced, which acted upon the glass.

As Berzelius found 100 parts of fluor spar, when acted upon by sulphuric acid, to yield 175 parts of sulphate of lime, equal to 73.553 parts of lime, or 52.819 of calcium, it follows that 100 parts of fluoride of calcium should contain 47.181 of fluorine and 52.819 of calcium. By the assistance of this result, and further experiments, M. Kuhlman proceeded to ascertain the composition of hydro-fluoric acid. Dry muriatic acid gas was passed over calcined fluor spar heated to redness in a tube of platina; the fluoride of calcium was decomposed, free hydro-fluoric acid was evolved, and chloride of lime remained in the tube. The hydro-fluoric acid acted upon the glass tubes, but being received in water was entirely dissolved, with the exception of the silica it had separated from the glass: no trace of hydrogen appeared. One hundred parts of fluoride of calcium thus treated became 143.417 parts of chloride of calcium, the 52.819 parts of calcium having united to 90.598 parts of chlorine. But this latter quantity must have liberated 2.511 parts of hydrogen, which must, therefore, have combined with the 47.181 parts of fluorine in the spar, to form 49.692 parts of hydro-fluoric acid. This latter body, therefore, consists of 94.941 fluorine, and 5.059 of hydrogen per cent. A small quantity of chlorine was set at liberty during the experiment, the author thinks, from a little manganese in the fluor spar.

M. Kuhlman found that all the chlorides, when subjected to the action of anhydrous sulphuric acid in vapour, resisted decomposition, except the chloride of sodium, which gave a small quantity of sulphate of soda, and a double salt of soda and platina, crystallizing in fine needles of a yellow colour. No doubt is entertained that, in the latter case, the common salt and sulphuric acid were not perfectly dry.—_Bull. Univ._

14. _Crystallization of Phosphorous_.—By the fusion and careful refrigeration of a large quantity of phosphorus, M. Frantween has obtained very fine crystals of an octoedral form, and as large in size as a cherry-stone.

15. _Solutions of Phosphorus in Oils_.—The solutions of phosphorus in fixed oils are so luminous as often to be resorted to for the exhibition of this peculiar property of phosphorus; but M. Walcker has remarked, that the power which they ordinarily possess is instantaneously destroyed by the addition of small quantities only of certain other substances, as the essential oils. The rectified oils of turpentine and amber, the oils of rosemary, bergamotte, lemon, camomile, angelica root, juniper berries, and parsley seed, [p207] the oil obtained by the distillation of the nutmeg, all produce this effect when their quantity is not more than one-fiftieth part of the luminous oily solution of phosphorus. The same effect is produced by adding about a fifth of the oils of anniseed, cajeput, lavender, rue, sassafras, fern, cascarilla, mint, orange flowers, fennel, valerian, cherry laurel, or bitter almonds, or balsam of copaiba; but the oil of cinnamon, rectified petroleum, balsam of Peru, and camphor, have no such effect.—_Annal. der Phys._ 1826, p. 125.

16. _On the Inflammation of Powder when struck by Brass, &c._—Iron has been excluded from powder-works as subject to cause sparks by a blow, and brass and copper have been recommended in its place. M. le Col. Aubert has remarked, that brass on brass can inflame powder, and has made experiments on the subject before a committee, the result of which is as follows:—Inflammation of the powder takes place when the blow is given by iron against iron; iron against brass; brass against brass; iron against marble; lead against lead, or against wood, when the blow is produced by a leaden ball shot from a fire-arm. As yet the powder has not been inflamed by the blow of an iron hammer against lead or wood.—_Bull. de la Soc. d’Encouragement;_ _Bull. Univ._

17. _Cementation of Iron by Cast Iron_.—Pure iron, when surrounded by, and in contact with, cast iron turnings, and heated, is carbonised very rapidly, so as to harden, to temper, and, in fact, to exhibit all the properties of steel. M. Gautier finds this a very advantageous process in numerous cases, especially where the articles to be case-hardened, or converted into steel, are small, as iron wire, or wire gauze. The temperature required is not so high as that necessary in the ordinary process of cementation, and the pieces to be carbonised are not injured in form. The kind of cast iron used should be the gray metal, and the more minutely it is divided the more rapid and complete is the operation. By covering the mass of cast metal, in which the iron to be carbonised is enveloped, with sand, oxidation, from contact of the air, is prevented, and the cast metal may be used many times. Plumbago experimented with in the same manner does not produce the effect.—_Jour. de Pharmacie_, 1827, p. 18.

18. _On the Preparation of Ferro-prussiate of Potash, by_ M. Gautier.—Numerous investigations induced M. Gautier to conclude, that, i. When animal matter is calcined alone it yields but little cyanogen. ii. That when mixed with potash it gives more, but the cyanuret is not ferruretted. iii. That ammonia is then produced in large quantity. iv. That the substitution of nitre for potash, and the addition of iron or scales of iron, augmented the production of cyanogen, and gave a ferro-prussiate. The following is the process of manufacture to which M. Gautier has ultimately arrived, [p208] and which he has practised for some years. The proportions of the materials are—

Blood, considered as in the dry state, 3 parts Nitre 1 part Iron scales 1/50 of the blood employed.

The blood is first to be coagulated in a large copper cauldron, and the serum being separated by means of a press, the coagulum is to be returned to the cauldron with the nitre and iron. The quantity of water contained in the blood is sufficient to liquify the salt, so as to allow of an uniform mixture being effected. The mixture is then removed, and exposed in an airy situation to dry, the putrefaction of the blood being prevented by the nitre. When the desiccation is complete, the mixture is charged into cast iron cylinders, which are fixed in a reverberatory furnace, and in all things resemble those used in the preparation of animal charcoal. These are to be raised to a brown red heat, until no more vapour is disengaged, and then left until nearly cold, after which the contents are to be withdrawn and put into a wooden vat, with twelve or fifteen times their weight of water, for an hour. The fluid is then to be filtered through a cloth, and evaporated until of 32° of Beaué (specific gravity 1.284.) Being then left to cool, a large quantity of well-crystallized bi-carbonate of potash is obtained. M. Gautier says he has not, as yet, been able to explain how it is that this bi-carbonate has been formed at so high a temperature; a portion also appears to be decomposed during the evaporation of the solution, which, at first but slightly alkaline, becomes sensibly so by a prolonged evaporation.

As the same product is not obtained when potash is used in place of nitre, it is probable that the elements of the nitric acid perform a particular part in the operation.

The solution which has given the crystals of carbonate of potash contains a little carbonate of potash, and much ferro-prussiate of potash. It is to be concentrated to 34° (specific gravity 1.306), and placed in wooden vessels lined with lead. In the course of some days a greenish crystalline mass is obtained, which being redissolved in a fresh quantity of pure water, and evaporated to 32° or 33° (specific gravity 1.295), is to be recrystallized.

Sometimes, when using potash, M. Gautier has mixed nitre with it, and has always obtained a richer product than when potash alone had been employed.—_Jour. de Phar._ 1827, p. 11.

19. _Sulphocyanide of Potassium in Saliva_.—MM. Tiedemann and Gmelin have observed the existence of this peculiar compound in saliva, in two cases; the one when the fluid was secreted during smoking, and the other when no such stimulus was applied.—_Ann. de Chimie_, xxxv. 266.

20. _Decomposition of Sulphate of Copper by Tartaric Acid_.—M. [p209] Planche has observed, that when sulphate of copper is dissolved in wine vinegar, for the purpose of preparing a corrosive liquid to be applied to corns on the feet, that the tartaric acid present in the vinegar displaces the sulphuric acid from a part of the salt, and an insoluble acid tartrate of copper is produced.

21. _Separation of Arsenic from Nickel or Cobalt_.—The following process by M. Woehler seems among the best of those intended for freeing nickel or cobalt from arsenic in the dry way. It is founded upon the circumstances that many alloys, when heated with sulphuret of potash, become changed into a mixture of sulphurets, and that sulphuret of arsenic is very soluble in sulphuret of potash. One part of kupfernickle, fused and reduced to fine powder, is to be mixed with 3 parts of carbonate of potash, and 3 parts of sulphur, in a covered Hessian crucible. The heat is to be gradually raised to redness, and until the mass is just entering into fusion, and by no means so highly as to fuse the sulphuret of nickel which is formed. When cold, water is to be added, which will dissolve the sulphuret of potash, and leave a yellow crystalline powder, which is sulphuret of nickel, retaining, perhaps, a little copper or cobalt, but no arsenic, if the operation has been well performed. When, however, the object is to have the nickel perfectly pure, it should be fused a second time with sulphur and potash.

The method of freeing cobalt from arsenic, is the same as for nickel; but it is then necessary to perform the operation a second time. The cobalt (that of Tunaberg) has never been perfectly freed from arsenic by one operation, but has never retained any after the second.—_Archiv für Bergbau_, 1826, p. 186.

22. _Compounds of Gold_.—According to late experiments of Dr. Thomson, peroxide of gold consists of

1 atom gold 25 3 " oxygen 3 --- 28

and is consequently a teroxide. Muriate of gold consists of

2 atoms muriatic acid 9.25 1 " per oxide of gold 28. 5 " water 5.625 ------ 42.875 _Edin. Journal_, p. 182.

23. _Chemical Researches relative to certain Ancient Substances_.—M. Vauquelin has analyzed, i. A poignard blade formed of copper only;