Chapter 7

The principal tests were made through the conduits on Market Street, laid by the National Underground Electric Company as far as Ninth Street. A cable of five conductors was laid through the conduit. Two of these conductors consisted of simple "circuit wires," while the other three were what is known as "solenoids." A solenoid wire is a single straight wire, connected at each end with and wound closely around by another insulated wire, this forming a complete system, the electric currents returning into themselves. Electricians claim that the solenoid effectually overcomes all induction, and this afternoon experiments were made for the purpose of proving that assertion. In the telephones, connected by the ordinary wires, a constant burr and click could be heard, that sound being the induction from the wires on the poles on Market Street, sixty feet overhead. With the solenoid the only sound in the telephones was the voices of the persons speaking. The faintest whispers could be heard distinctly, and the ease and comfort of conversation was in marked contrast to the other telephone on the ground wires. A set of telegraph indicators was also attached to the wires in use in the cable. The sounds were transferred from one "ground wire" to the other, while the solenoids seemed to resist every influence but that directed upon them by the operators. Another interesting test was made. The electric current for a Hauckhousen lamp was passed through a long coil of solenoid wire. Separated from this coil by a single newspaper, lay a coil of wire attached to telephones, yet not a sound could be heard in the telephones but the voices of the persons using them. The current of electricity created by a dynamo-electric machine is of necessity a violent one, and in the use of ordinary wires the induction would be so great that no other sounds could possibly be heard in the telephones.

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DR. HERZ'S TELEPHONIC SYSTEMS.

In an article by Count du Moncel, published in SCIENTIFIC AMERICAN SUPPLEMENT, No 274, page 4364, the author, after describing Dr. Herz's telephonic systems, deferred to another occasion the description of a still newer system of the same inventor, because at that time it had not been protected by patent. In the current number of _La Lumière Electrique_, Count Moncel returns to the subject to explain the principles of these new apparatus of Dr. Herz, and says:

I will first recall the fact that Dr. Herz's first system was based upon the ingenious use (then new) of derivations. The microphone transmitter was placed on a derivation from the current going to the earth, taken in on leaving the pile, and the different contacts of the microphone were themselves connected directly and individually with the different elements of the pile. The telephone receiver was located at the other end of the line, and when this receiver was a condenser its armatures were, as a consequence of this arrangement, continuously and preventively polarized, thus making it capable of reproducing conversation.

This arrangement evidently presented its advantages; but it likewise possessed its inconveniences, one of the most important of these being the necessity of employing rather strong piles and consequently of exposing the line to those effects of charge which react in so troublesome a manner in electrical transmissions when they occur on somewhat lengthy lines. Now the fact should be recalled that Dr. Herz's principal object was the application of the telephone to long lines, and he has been applying himself to this problem ever since. He at first thought of employing reversed currents, as in telegraphy; but how was such a result to be attained with systems based upon the use of sonorously-vibrating transmitters? He might have been able to solve the problem with the secondary currents of an induction bobbin, as Messrs. Gray, Edison, and others had done; but then he would no longer have been benefited by those amplifications which are furnished by the variations of pressure-derivations in microphones, and this led him to endeavor to increase the effects of the induced currents themselves by prolonging their duration, or rather by combining them in such a way that they should succeed each other, two by two, in the same direction; and this is the way he solved the problem in the beginning.

The fact should also be recalled that Dr. Herz had, from his first experiments, recognized the efficiency of those microphonic contacts that are obtained by the superposition of carbon disks or other semi-conducting substances. He has employed these under different arrangements and with very diverse groupings, but, as a general thing, it has been the horizontal arrangement which has given him the best effects.

Let us suppose, then, that four systems of contacts of this nature are arranged at the four corners of an ebonite plate, C C (Figs. 1 and 2), at A, A¹, B, B¹, and that they are connected with each other, as shown in the cuts--that is to say, the upper disks, _e_, _f_, _g_, _h_, parallel with the sides of the plate, and the lower disks, A, A¹, B, B¹, diagonally. Let us admit, further, that the plate pivots about an axis, R; that the disks are traversed by small pins fixed in the plate; and that small leaden disks rest upon the upper disks. Finally, let us imagine that the plate is connected at one end, through a rod T, with a telephone diaphragm. Now it will be readily understood that the vibrations produced by the diaphragm will cause the oscillation of the plate, C C, and that there will result therefrom, on the part of the disks, two effects that will succeed one another. The first will be, for the ascending vibrations, an increase of pressure effected between the disks of the left side, by reason of their force of inertia being increased by that of the lead disks; and the second will be, for the disks to the right, and, for the same reason, a reduction of pressure which will take place through resilience, at the moment of change in direction of the vibrating motions.

If the current from a pile, P, traverses all these disks, through the connections that we have just mentioned, and passes through the primary helix (through the wire, I) of an induction coil H H' (Fig. 2), located beneath the apparatus, and if the secondary current from this bobbin corresponds, through the wire I, with a telephone line in which there is interposed a telephone or a speaking condenser, there will be set up an inverse induced current, which, being reversed as a consequence of the crosswise connections of the disks, will continue the action of the first or increase its duration, and, consequently, its force, through the telephone receiver.

The results of this system are very good; but Dr. Herz has endeavored to simplify it still further, and with this object in view has experimented on several arrangements. For example, to obtain inversion a contact was simply placed on each side of the vibrating plate. Although the movements of this latter are not, as we know, of the nature of ordinary sonorous vibrations, it was thought that they might prove to be in opposite directions on the two sides of the plate, and that one of the contacts might be compressed while the other was free. So notwithstanding the advantages of this arrangement, it was thought necessary to place the plate vertically in order to give the same regulation to the two contacts which it is essential should be identical. But it became difficult to regulate by weight; and even to succeed in regulating at all, it became necessary to employ two parallel diaphragms, vibrating in unison, and each carrying its contact, but in opposite directions. Afterwards, the horizontal arrangement was again adopted; but, by a clever combination, the two principles applied by Dr. Herz--derivation and inversion--were united. The current is then led to a double contact, where it divides. This contact is arranged under the plate in such a way that its two points of variable resistance act in opposite directions to each other, or, in some apparatus, so that one of the points has no variation, while the other is in action. The result that occurs may be easily imagined. The system has been experimented with under different forms; in one case the derivation is simple, that is, a single one of the currents being sent into the line, while in another case it is double, each of the branches being provided with a bobbin and communicating with the receiver. In the latter case the result is remarkably good, but the apparatus is not free from a certain amount of complication, and demands, moreover, particular care in its construction, experience having shown that the induction coils must not be equal, but that they must present resistances combined according to the circuit doing duty. It should be added that researches have been continued as to the bodies proper to be employed as microphonic contact, with the result of bringing out the important fact that the number of substances that can be put to this use is almost unlimited. The contacts of the Herz apparatus are now being made of conducting bodies (metals for example) reduced to powder and conglomerated by chemical means with a sort of non-conductive cement. The proportion of the elements depends upon the conductivity of the materials employed, and it alone determines the microphonic value of the compound, the nature of the elements apparently having scarcely any influence.

Nor has the speaking condenser been neglected. As regards this, efforts have seemingly been made toward finding a convenient arrangement and a regular mode of construction, the good working of these apparatus being absolutely dependent upon the care with which they are set up.

In Dr. Herz's opinion, the telephone is not to remain a single apparatus, varied only as to form, but, on the contrary, must be actually modified according to the purposes for which it is designed. He thinks that a telephone operating at great distances must differ from a city apparatus, and that an instrument for transmitting song can not be absolutely the same as one for conversational purposes. So he has endeavored to create types that shall prove appropriate for these different applications.

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DECISION OF THE CONGRESS OF ELECTRICIANS ON THE UNITIES OF ELECTRIC MEASURES.

For these measures there are adopted the fundamental unities--centimeter, gramme, second, and this system is briefly designated by the letters C., G., S. The practical units, the _ohm_ and the _volt_, will retain their present definitions; the ohm is a resistance equal to 10^{9} absolute unities (C., G., S.), and the volt is an electromotive force equal to 10^{8} absolute unities (C., G., S.). The practical unit of resistance (ohm) will be represented by a column of mercury of 1 square mm. in section at the temperature of 0°C. An international commission will be charged with ascertaining for practice, by means of new experiments, the height of this column of mercury representing the ohm. The name _ampère_ will be given to the current produced by the electromotor force of 1 volt in a circuit whose resistance is 1 ohm. _Coulomb_ is the quantity of electricity defined by the condition that in the current of an ampère the section of the conductor is traversed by a coulomb per second. _Farad_ is the capacity defined by the condition that a coulomb in a condenser, whose capacity is a farad, establishes a difference of potential of a volt between the armatures.

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SECONDARY BATTERIES.

By J. ROUSSE.

In order to accumulate electricity for the production of light or motive power, the author has arranged secondary batteries, which differ from those of M.G. Planté. At the negative pole he uses a sheet of palladium, which, during the electrolysis, absorbs more than 900 times its volume of hydrogen. At the positive pole he uses a sheet of lead. The electrolyzed liquid is sulphuric acid at one tenth. This element is very powerful, even when of small dimensions. Another secondary element which has also given good results, is formed at the negative pole of a slender plate of sheet-iron. This plate absorbs more than 200 times its volume of hydrogen when electrolyzed in a solution of ammonium sulphate. The positive pole is formed of a plate of lead, pure or covered with a stratum of litharge, or pure oxide, or all these substances mixed. These metallic plates are immersed in a solution containing 50 per cent. of ammonium sulphate. Another arrangement is at the negative pole, sheet-iron; at the positive pole a cylinder of ferro-manganese. The electrolyzed liquid contains 40 per cent. ammonium sulphate.

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THE TREATMENT OF QUICKSILVER ORES IN SPAIN.

Though known from remote times, the date of the first opening of the famous mines of quicksilver of Almadén has not been precisely determined. Almost all the writers on the subject agree that cinnabar, from Spain, was already known in the times of Theophrastus, three hundred years before the Christian era, although there is evidence in the writings of Vitruvius that they were worked at a still earlier date, Spanish ore being sent to Rome for the manufacture of vermilion. Such ore constituted a part of the tribute which Spain paid to Rome emperors, and there are records of its receipt until the first century after Christ. The history of Almaden during the reign of the Moors is so much involved in doubt that some writers deny altogether that the Arabs worked the deposit; still the very name it now bears, which means "the mine," and many of the technical terms still in use, give evidence that they knew and worked that famous deposit. As for their Christian conquerors, there are stray indications that they extracted mercury during the twelfth and thirteen centuries. In 1417, Almaden was given the privileges of a city, and from 1525 to 1645 the working of mines was contracted for by the wealthy family of Fugger, of Augsburg, Germany. Since then, the mine has been worked by the state, though the Rothschilds have controlled the sale of the product.

According to Vitruvius, the works for manufacturing vermilion from Spanish ore in Rome were situated between the temple of Flora and Quirino. The ore was dried and treated in furnaces, to remove the native mercury it contained, and was then ground in iron mortars and washed. In addition, small quantities of quicksilver and vermilion were made at Almaden. The ancients describe other methods, among which Theophrastus speaks of using vinegar, which, however, appears from modern investigations to have been an erroneous account. Nothing definite is known concerning the methods of the Moors; we possess only as a proof that they produced mercury, an account of a quicksilver fountain in the marvelous palace of Abderrahman III., at Medina-Zahara, and the works of Rasis, an Arab. The Moors probably extracted mercury at Almaden, from the eighth to the twelfth century, by the use of furnaces called "xabecas," which latter, in the fourteenth century, were still employed by the Christians, who continued them till the seventeenth century, when German workmen replaced them by "reverberatory" furnaces, which in turn were superseded in 1646 by aludel or Bustamente furnaces. There is an anonymous description of the working with xabecas as practiced at Almaden in 1543, and later accounts in 1557 and 1565. The ore was put into egg-shaped vessels with a lid, the mineral being covered over with ashes. The vessels were packed in a furnace heated with wood, about 60 pounds being used per pound of quicksilver made. This system was also applied at the Guancavelica mines, discovered in Peru in 1566, where the xabecas were abandoned in 1633, being replaced by the furnaces invented by Lope Saavedra Barba, which there were called "busconiles," while in Spain they were named Bustamente furnaces, and elsewhere aludel furnaces. They were introduced at Almaden thirteen years after their first use in Peru by Juan Alfonso de Bustamente, Barba and his son having been lost at sea on their way to the Peninsula. In 1876, there were at Almaden, at the works at Buitrones, twenty such aludel furnaces and two Idria furnaces. D. Luis de la Escosura y Morrogh, from whose work we take the above notes, has followed the historical details of the growth of Almaden closely, and from his account of the method of working in 1878 we take some data:

It is not an easy matter to explain the classification of the ore at Almaden. _Metal_ is there called the richest mineral, composed of quartz impregnated with crystalline cinnabar. _Requiebro_ are middlings of medium richness, _China_ are smalls, and _Vaciscos_ the finest ore. Besides native mercury, which the ores of Almaden contain in greater or smaller quantity, the most abundant mineral is cinnabar, which is always crystalline and is often crystallized. The ores have, besides, a small quantity of selenium and iron pyrites intimately mixed with the cinnabar. The gangue is quartz, occasionally argillaceous and bituminous. The following are assays of some of the ores made by Escosura:

Metal. Requiebro. Vaciscos. China. 1 2 3 4 5 6 7 8 Cinnabar 29.1 21.2 13.3 10.2 5.1 2.8 1.2 0.86 Iron pyrites. 2.2 2.0 2.0 1.9 12.3 1.5 2.1 2.80 Bituminous matter 0.6 1.0 1.0 1.2 4.6 0.7 3.4 0.90 Gangue 67.5 74.8 82.1 76.5 77.5 93.3 90.2 93.50 ---- ---- ---- ---- ---- ---- ---- ----- Total 99.4 94.0 98.8 98.9 99.5 98.3 98.7 98.06 Quicksilver 25.05 18.28 11.47 8.64 4.40 2.41 1.03 0.75

It appears to be a difficult matter to determine the average percentage of the various grades of ore. In 1872, a commission classified and sampled a lot of 300 tons with the following results:

Quantity, Per cent. Average of Grade. No. kilos. mercury. grade.

Metal { 1. 81,890 23.86 } { 2. 14,970 22.65 } 24.80

Requiebro { 3. 12,240 15.20 } { 4. 17,000 10.50 } 12.47

China { 5. 31,890 3.84 } { 6. 32,360 1.17 } 1.75 { 7. 28,960 0.10 }

Vaciscos 8. 78,320 9.24 9.24

This general average of 12.28 per cent. of mercury is pronounced higher than the usual run of the ore, which, it is stated, does not go above 7 to 8.50 per cent.

The furnace in which the ore is treated is cylindrical, 2 meters in diameter, and 3.70 meters high from a brick grate, supported by three arches to the arched roof. At the level of the grate is a charging orifice, and near the roof are openings into two chambers, from the bottom of which extend 12 lines of aludels, clay vessels, open at both ends, the middle being expanded. The mouth of one fits into the back end of the one following, a channel being thus formed through which the fumes to be condensed are passed. The lines of aludels which are laid on the ground terminate in a chamber, and for half the distance between the furnaces and these chambers the ground slopes downward, while for the other it slopes upward. Two furnaces are always placed side by side, and the pair have from 1,100 to 1,150 aludels.

The operation is as follows: A layer of poor quartz is spread over the brick grate; this is followed by a layer of smalls, and then by a layer of still finer stuff, all of it being low grade ore. On top of this are piled two-thirds of the _china_ of the charge on which the _metal_ is put. Then follows a layer of _requiebro_, another lot of _china_, and finally the _vaciscos_, shaped into balls, the whole charge amounting to about 11½ tons, which is put in from an hour and a half to two hours by three men. The charging orifice is then closed, the aludels are luted, and everything made tight. The fires under the brick grate are lighted and kept going for twelve hours, during which time furnaces, charge, and condensing apparatus are heated up. During this period, the temperature in the condensing-chamber at the end of the line of aludels runs up 40 or 50 degrees Celsius, and some mercury, evidently part of the native quicksilver, is noticed in it.

The temperature of the aludels in the immediate vicinity of the furnaces is about 140 degrees C. During this period, the consumption of fuel is four parts to every part of quicksilver produced. At its close, the fire is drawn, and the second period begins. The air entering through the brick arch is heated to from 200 to 300 degrees by contact with the layer of poor stuff, the cinnabar is ignited, and its sulphur oxidized, and the quicksilver vaporized and, condensing in the aludels, flows toward the depression in the central portion of the line. The temperature goes on increasing, until, twelve hours after the beginning of this period, the thermometer shows 212 degrees C. at the first aludels. This lasts for 18 hours, and then the third or "cooling period" begins, which takes from 24 to 26 hours, and during the beginning of which the temperature in the furnaces still rises. It is then opened and cooled down. A very elaborate series of observations made on the temperatures of various parts of the condensing apparatus of the Almaden furnaces has shown that at the aludels nearest to them the heat increases steadily until it reaches 249 degrees C., 44 hours after the beginning of the operation; that in the middle of the line, at the depression, the maximum is 50 degrees 50 hours after starting the fires; and that at the end it does not surpass 39 degrees. In the final condensing chamber, the temperature varied, running downward from 40 degrees during the heating period to 14 degrees, rising again to 29 degrees toward the close.

The loss of the quicksilver during the operation has been vary variously estimated, some stating that it is 50 per cent. and more, while others place it at 30 per cent. Escosura, in his work, gives the details of an operation checked by a royal commission in 1872, according to which the loss in working ore running 9.55 per cent. was only 4.41 per cent.--a loss which he considered inevitable. In 1806, two Idria furnaces were put up at Almaden, but the engineers are not favorably impressed with them. The first cost is stated to be more than ten times greater than that of an aludel furnace, while the capacity is only 50 per cent. greater. One pair of Idria furnaces in five years produced 120,000 kilogrammes of quicksilver, against 843,000 kilogrammes made by eight sets of the Bustamente furnaces, the cost per kilogramme of quicksilver being respectively 0.121 and 0.056 peseta.

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THE BALLOON IN AERONAUTICS.

While it is undoubtedly true that the discovery of the balloon has very greatly retarded the science of aerostation, yet, in my opinion, its field of usefulness as a vehicle for pleasure excursions, for explorations, and for scientific investigations, has not been fully developed for the want of certain improvements, the nature of which it is the object of this paper to point out. The improvement of which I am about to speak relates to the regulation of the buoyancy of the balloon. This is now done by throwing out ballast or by allowing some of the gas to escape--a method which necessitates the carrying of an unwieldy amount of sand and the expenditure of an unnecessary amount of gas.