occasioned by the formation of an arc upon one side of the point (in place of a symmetrical brush), which traversed around the points as they wore away, emitting much the largest part of the light through a small are of radiation in the horizontal plane, and presenting on one side of the points a brilliant reflection from them, and a corresponding obscuration on the opposite side. This difficulty was met and overcome by the adaptation of carbons of suitable sectional dimension for the current of electricity employed, until a uniform brush, emitting rays of very nearly equal value in all directions, was obtained. The Franklin Institute experiments consequently do not give the value of an apparent maximum of effect but the mean effect from the electric lamps experimented with.

"For a practical datum it may be well to state, in conclusion, that the result of 380 candles per horse-power is, that 90 pounds weight falling one foot per minute represents the power demanded to afford a light of the best spermaceti candle by means of the dynamo-electric system. A man ascending a flight of steps at very moderate rate will have exerted a force equal to three candles. And the results claimed by many makers of dynamo-electric machines are four to five times as good as these.

"The problem of electric lighting to-day is the production of small enough quantity of light with equal economy to that attained for large illuminating effects, and of the distribution into small sources of light of the great light capacity now obtained at a single point of emission. To these ends the intelligence of all electricians is now directed, and the attainment of some measure of success can be confidently anticipated."

Coret's Thermometer.-Coret solders end to end many concentric tubes of different metals, steel and zinc for example. By alternating the joints the differences of dilatation are added, so that the last tube, being connected with a toothed wheel or series of levers, gives a great motion to a needle, sufficient to indicate small fractions of a degree of temperature. The metals being good conductors, the indications are rapid when the metallic mass is placed in contact with any body of which the temperature is desired. The tubes can be concentrated in a space of less than two centimetres (79 inch). The thermometer is, therefore, very convenient for medical use.-Bull. de la Soc. d'Encour

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A NOTE ON THE ARTIFICIAL PRODUCTION OF DIAMONDS BY THE PROCESSES OF DESPRETZ.

By Prof. EDWIN J. HOUSTON.

In 1849 Despretz endeavored to produce diamonds artificially by the direct fusion of carbon. For this purpose he combined the heat of the voltaic arc, the sun's heat, concentrated by means of a large lens, and the flame of a powerful blowpipe. The pile consisted of 185 pairs of Bunsen cells. Fragments of nearly pure anthracite, placed in this powerful heat focus, he claims, were observed to melt and fall in drops. He gives an account of these experiments in a note read before the French Academy of Sciences at the séance of June 18, 1849.*

Later, in 1849, he obtained undoubted evidences of the volatilization of carbon by exposing it to the heat of a voltaic arc obtained from a battery of 496 elements, arranged in four parallel series.†

In 1850, by means of a battery of 600 Bunsen elements, connected with a second battery of 135 elements, he succeeded in partially fusing a piece of hard retort carbon, which was thereby converted into pure graphite.‡

By none of these experiments, however, was he able to obtain any positive evidence of the crystallization of carbon.

Notwithstanding these failures he continued his experiments for several years. Abandoning the methods of sudden fusion and volatilization, he tried a number of experiments, all based on the gradual deposition of volatilized material. In one of the most successful of these experiments, the carbon was slowly volatilized in a vacuum, by the continuous discharge of a Ruhmkorff induction coil. A small cylinder of pure carbon placed at one electrode, was gradually deposited in a crystalline state on platinum wires attached to the other electrode. The electrical discharge was continued without interruption for one month, at the end of which time, by the aid of a microscope, octahedral crystals were plainly visible.

* Comptes Rendus, Tome 28, p. 755. + Comptes Rendus, Tome 29, p. 48. Comptes Rendus, Tome 30, p. 367.

Apparently no commercial application was ever made of these processes, no doubt on account of the length of time required for the deposition. The present advanced state of electrical science, however, may before long suggest some modifications of these processes that may make them more practicable.

The public interest in the artificial production of the diamond will, I think, warrant my translating the first part of M. Despretz's original paper containing a brief account of the process. It is entitled:

“OBSERVATIONS ON CARBON, AND ON THE DIFFERENCE OF TEMPERATURE OF THE LUMINOUS POLES PRODUCED BY INDUCTION.*

"The results of the experiments that I had the honor of presenting to the Academy, some few years ago, on the fusion and volatilization of certain bodies, especially carbon, show that it is neither by fusion nor by the sudden volatilization of carbon, that we may hope to obtain this body crystallized.

"We have shown by these experiments that pure carbon melted, and that the diamond melted, form only amorphous graphite; that carbon suddenly volatilized on the walls of a flask gives only a dark powder without any appearance of crystallization.

"These experiments on the fusion and volatilization of carbon are now repeated every year in the course on chemistry and physics at the Sorbonne. We can obtain by the heat of the arc a number of crystallized bodies. I hope I may return to this point. The same results would probably be obtained for carbon if we had crucibles less fusible than this substance, which we do not possess. I have, therefore, had recourse to another process. The process which has given me the best success is founded on a gradual volatilization produced by induction

currents.

"I took a flask with two tubulures, arranged as for the electrical egg; to the lower rod I attached a cylinder of pure carbon, a few centimetres in length and one centimetre in diameter. I attached to the upper rod a dozen thin platinum wires; I produced a vacuum in the flask; then, the distance between the wires and the carbon being from 5 to 6 centimetres, I caused to pass the current of an induction apparatus constructed by M. Ruhmkorff, and which has been described in several notes presented to the Academy. The arc was reddish from

* Comptes Rendus, Tome 37, p. 369.

the carbon to within a short distance of the platinum; the portion which enveloped the extremity of the platinum wires was of a bluishviolet.

We

"This arrangement of apparatus was always adhered to. placed the bundle of platinum wires above, in order not to confound the minute sparks from the carbon, with the crystals which we wished to form.

"The pile was composed of four Daniell's elements, connected two by two.

"The experiment continued uninterruptedly for a month, excepting the time necessary to recharge the pile. There was deposited a thin black layer of carbon on the wires. This layer, viewed by a lens, did not present any very distinct appearance; with a compound microscope, with a magnification of about thirty times, it presents several interesting points.

"I saw over the wires, and particularly at the extremities, particles separated one from another, which seemed to belong to the octahedral system.

"I saw, also, on the black layer, but none at the extremities, seyeral small octahedra resting on a summit.

"I repeatedly examined the wires, and always found the same things.

"An able and skilled crystallographer has recognized black octahedra, truncated at the extremities, and little white octahedra resting on a summit.

"I did not previously inform my colleague, M. Delafosse, what I observed.

"I substituted for the wires a polished platinum plate, 1 centimetres in diameter; although this experiment continued in activity for almost six weeks, yet there was no deposit of crystals on the plate. The plate was covered over at least half of its surface with almost circular curves, with radii somewhat larger than that of the plate ; each of these curves was painted with one of the colors of thin films. We saw here and there small greyish-white spots of powder, which appeared to be the result of the momentary adherence of isolated deposits.

"In another experiment I fixed a cylinder of pure carbon to the positive pole of a feeble Daniell pile, and to the other pole a platinum wire; I then plunged the two poles in water slightly acidulated. The

experiment continued for more than two months; the negative pole was covered with a black layer.

"Nothing was discovered in this layer by an examination with a microscope.

"I requested M. Gaudin, known to the Academy by different researches, to try both products on hard stones.

"He proved, in my presence, that the small quantity of material that surrounded one of the dozen wires of platinum, mixed with a little oil, sufficed to polish in a short time several rubies.

"The black powder deposited in the humid way, although much more considerable in quantity, required more time to produce the same polish.

"We know that the diamond is the only body which polishes the ruby; therefore M. Gaudin has not hesitated to consider both materials as the powder of the diamond.

"I have made a great many experiments during two years; I give here the two which afford the most interesting results."

In connection with the above we note a communication to the French Academy of Sciences,* from M. Lionnet, in which he claims to have made, in 1846 and 1847, experiments on the crystallization of carbon. These experiments, since forgotten, were recalled by a communication of Chancourtois † to the Academy. M. Lionnet claims to have used the following process: A voltaic couple, formed of platinum and tin, was plunged in a small vessel filled with carbon bisulphide, under the action of the weak current so developed, decomposition of the electrolyte occurred, the sulphur combining with the tin, while the carbon, the author claims, was deposited in a crystalline condition on the bottom of the vessel. It would seem that if deposited at all under these conditions, it would be on the surface of the platinum. Central High School, Philadelphia, Aug., 1880.

Lunar Geology.-J. Landerer has submitted to the Academy a work in which he seeks to determine the lithologic character of our satellite. He thinks that the density of the moon, and the angle under which it polarizes the light of the sun, are such as to show that the materials of the surface are analogous to those of the silicate rocks.— Comptes Rendus.

*Comptes Rendus, Tome 63, p. 213.

Comptes Rendus, Tome 63, p. 22.

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