II. CHEMICAL SCIENCE.

1. On the Conducting Power of Bodies for Heat, and on a new instrument called a Thermometer of Contact, by M. Fourier.-A memoir on these subjects by M. Fourier is inserted in the 'Annales de Chimie, xxxvii. p. 291,' which contains not only the description of two new instruments, with their applications and some novel results obtained by their means, but also the mathematical developement of the theory of these instruments, and of the experiments made with them.

The instrument called a thermometer of contact, consists of a conical vessel constructed of very thin iron, with the exception of the bottom, which is made of thin pliable skin; it is filled with mercury and has a thermometer, the bulb of which is immersed entirely in the mercury, and the scale has degrees of such magnitude that they may be divided into tenths. The skin must be preserved perfectly clean and never be overheated: it is better than any other similarly flexible substance, because of its superior conducting power. This instrument is to be accompanied by a support consisting of a block of marble; and any substance operated upon is to be in sheets or reduced to thin plates. When an experiment is to be made, the sheet, cloth, or thin plate is to be placed upon the marble, both being at the temperature of the room; the conical vessel, with its contents, is to be heated on a stove or other hot body, until about 46° or 47° C.; and then being removed, at the moment it has fallen to 45°, it is to be placed on the substance to be tried; the time when it arrives at 40° is to be exactly noted by a watch, and then the temperature noted minute by minute for five minutes. If the experiment be repeated with the same substance on another part of the marble, exactly the same results will be obtained, provided the temperature of the place has not changed. If the experiments are to be made on rigid plates, then these are not to be placed directly upon the marble, but upon a mercurial cushion, made by confining mercury under a surface of skin.

If the substance first tried be replaced by another, and then the fall of temperature in a given time be noted, the variation will be found very sensible, however slight the difference between the substances; the addition of a single sheet of the finest paper makes a great difference in the effect. The slightest difference in the nature of the stuff is immediately indicated. If a piece of linen cloth be replaced by flannel, or by woollen cloth, or a thin piece of woollen cloth by a thick piece, not only are the differences produced very evident, but they can be obtained over and over again with the utmost constancy, care being taken that the pressure of the mercury upon the skin, and therefore upon the substance, be the same in all cases.

The same instrument also indicates the heat of contact of bodies. In such cases, after being heated as before mentioned, it is

to be placed on a thick mass of the substance to be tried, and the fall of temperature in a given time noted as before; striking effects were thus obtained. Being first applied to iron at the temperature of 8° C., and then upon a mass of stone, the difference at the end of the second minute was 5°. The differences are much greater when iron is compared with brick or wood.

Although the conducting powers thus obtained for different substances are only approximations, yet there are many bodies, as bricks, stones, wood, clothing, &c., for which these are quite sufficient.

Another still more delicate method of ascertaining the conducting power of bodies is then described, but it is also more difficult. Two vessels are used; the lower one is maintained at a constant temperature, as 100° C.; upon that is placed the substance to be tried, and upon that again the upper vessel. The lower part of the upper vessel is inclosed, and constitutes the bulb of an air thermometer; the upper part is retained at the temperature of ice; the air therefore in the thermometer is cooled by the ice and warmed by the lower heated vessel; the latter producing an effect greater or smaller according to the nature of the substance between it and the air-vessel; the temperature of the air and the indication upon the scale connected with it soon becomes permanent, and as it is higher or lower, indicates the greater or less 'conducting power of the interposed substance. When the experiments are carefully made, they accord with those of the former instrument, but are more delicate.

By means of these instruments, M. Fourier was able to ascertain that many substances when put together conducted heat differently, according to the order in which they were placed. Two pieces of cloth being put between the instrument and the marble, the order of substances traversed by the heat, was skin, cloth-cloth, marble. After observing the effect, a thin plate of copper was placed between the cloth and the marble; the fall of temperature was then slower than before: the copper was then placed between the pieces of cloth, and the cooling was as if no copper were present; then placing the copper beneath the skin of the instrument and above the cloth, so that the order was skin, copper, cloth, cloth, marble, the temperature diminished more rapidly than if no copper had been there: thus the interposition of the metal facilitated the transmission of heat from the skin to the cloth, but diminished the transmission from the cloth to the marble.

2. On a Method of Measuring many Chemical Actions.-M. Babinet proposes to measure chemical action in cases where gases are generated, by ascertaining the force exerted by the gas evolved. The general cases enumerated are those in which hydrogen, nitrous acid, oxide of azote, carbonic acid, chlorine and sulphurous acid are disengaged. "If the operations

are carried on in close vessels, when the gas acquires a sufficient elastic force, the chemical action will stop; it is suspended until the moment when freedom is given to the compressed gas, the force of which in some sort makes an equilibrium to the chemical action which tends to disengage it." It is this elastic force which M. Babinet proposes to use as a measure of the action of different substances at various temperatures.

In 1818, a copper shell closed by a stop-cock was filled with zinc, water, and sulphuric acid, and being left on the snow it did not burst. In 1819 a copper tube was filled with the same substances, but it again was strong enough to resist the efforts of the gas to burst it. A vessel was then prepared and supplied with a gauge, in which the height of the mercury was to "give the elasticity of the gas at the moment when the equilibrium was established and the chemical action counterbalanced." At 25° C. (77° F.) the hydrogen disengaged from water, zinc, and sulphuric acid surpassed 33 atmospheres.

Another experiment was made by attaching a small copper globe to the apparatus, allowing communication between the two, then removing the globe and ascertaining how much gas it contained at 10° C. (50° F.) The globe, removed from the preceding chemical re-action, was found to contain thirteen times as much gas as under the ordinary pressure of the atmosphere; "the disengagement was therefore arrested here with a force of thirteen atmospheres."

At 0° (32° F.) M. Babinet supposes the force of hydrogen gas would be much feebler, and, employing iron instead of zinc, still more feeble. At ordinary temperatures, chlorine from muriatic acid and oxide of manganese has an elasticity not much more than two atmospheres.-Ann. de Chimie, xxxvii. 183.

We are uncertain what is M. Babinet's real meaning, though we quote his words accurately. That the chemical action is not arrested by the pressure from the evolved gases, or even influenced, except in the destruction of that mechanical action, which, when gases are evolved, is so active in mixing the ingredients concerned together, has been sufficiently shown in Mr. Faraday's experiments upon the liquefaction of gases. When carbonate of ammonia and sulphuric acid are put together and sealed up hermetically in a tube, although the evolution of carbonic acid gus ceases in a few hours or a day or two, still the chemical action goes on, and the evolution of liquid carbonic acid continues until no more of the carbonate remains to be decomposed. The same is the case with muriate of ammonia and sulphuric acid, and with many other mixtures. M. Babinet's process might give the elastic force of the gases or vapours of the substances produced, and be so far a measure of the mechanical effects of some chemical actions, but nothing else.-Ed.

3. On the formation of Fulgorites, or Lightning Sand Tubes.-Some

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very fine fulgorites have been shown in Paris and London by Dr. Fiedler, procured from Westphalia. Some of them, which, although not put together, have been exhibited in fragments and in drawings, were 19 feet long. These tubes consist of sand vitrified on the internal surface, and rough on the exterior; they are formed by the passage of lightning through a sandy stratum; and although this has been well determined, yet M. Hachette thought it might be well to add, to the knowledge already obtained, some experimental proofs of the effect of powerful electric discharges through powders of a convenient degree of fusibility.

The most powerful battery in Paris was employed, and the electricity accumulated in it discharged through powdered glass pressed into a hole made in a brick; tubes exactly similar to fulgorites were obtained, except that they were small and proportionate to the size of the electrical apparatus used. One was 25 millimetres (0.984 inches) long, the external diameter, diminishing irregularly from one end to the other, was from 0.118 to 0.059 of an inch, and its internal diameter 0.0197. In another experiment, made with glass and common salt mingled together, a regular tube 1.18 inch long was obtained, externally 0.157 of an inch wide, and internally of half that width.

Experiments made with powdered quartz and felspar did not succeed. The tubes, obtained as above, exactly resembled those formed naturally, in the brownness of the internal surface, but were very far short of them in solidity and strength,—a difference to be anticipated from the nature of the agents used.-Annales de Chimie, xxxvii. 319.

4. Preparation of Hydriodic Acid Gas.-The following process is by M. Felix d'Arcet. Hypophosphoric (hydro-phosphorous ?) acid is to be evaporated until upon the point of evolving phosphuretted hydrogen gas, when it contains no more water than is essential to its composition. It is then to be put into a small tube closed at one extremity, and its weight of iodine added; on applying a gentle heat, hydriodic acid gas is liberated, and continues to be evolved for a long time. The gas is perfectly pure, being free from excess of iodine; it may be collected over mercury without the formation of any iodide of mercury, or by letting the conducting tube descend to the bottom of the collecting jar in the ordinary manner for heavy gases. 90 or 100 grains of the acid gave as much as 120 cubic inches of hydriodic gas, pure and entirely absorbable by water. The residue of the operation is a mixture of phosphoric acid, and the compound of hydriodic acid and phosphuretted hydrogen. -Annales de Chimie, xxxvii. 220.

5. Test for Nitric Acid and its combinations.-Runge.-Pour a solution of protomuriate of iron upon the surface of an amalgam of

* See Proceedings of the Royal Institution, p. 434 of this Number.

zinc, and then place a crystal of nitre upon the latter in the fluid; a dark band immediately forms around the crystals, sometimes extending over the whole surface of the mercury. All the nitrates, as well as nitric acid, act in this manner; but other salts, as the chlorate,~ produce no effects of the kind; so that a very sensible test of the presence of nitric acid is thus afforded. It is necessary that the solution employed be a protosalt of iron. If nitric acid is supposed to exist in a liquid, it should be saturated with potash, evaporated to dryness, and the dry mass tried. Of course, salts of copper or of silver must not be present.

When an amalgam of brass is used instead of zinc, those effects are not produced; which M. Runge considers as a proof that the zine or brass is combined, chemically, with the copper.-Annalen der Physik, 1827, p. 479.

6. On the decomposition of Ammonia by the Metals.-It has usually been supposed, that when ammonia has been decomposed by the metals, as iron, copper, &c., the latter did not increase in weight ; · and although it had been remarked that they became brittle, it was considered as the result of some alteration in the arrangement of their particles. M. Savart, engaged in researches on the elasticity of bodies, had occasion to assure himself that there really was no increase in the weight of the metals used, and although he acknowledges that his experiments are as yet imperfect, still finds reason to believe the ordinary opinion erroneous. 141.91 grs. of thin copper wire were employed to decompose ammonia for four hours, and then had become 142.382, having increased 0.472. As the wire was slightly oxydized, the experiment was carefully repeated with 28.86 grs. of copper wire, the ammoniacal gas being dried, and every other precaution taken : the weight increased to 28.965, so that the wire had increased 45 of its weight, and had absorbed 0.105 of an unknown substance. The properties of the copper had been altered in the usual manner, and the specific gravity of the wire, which had been 8.8659, was now 7.7919.

Iron produced exactly the same effects, except that the increase 1? in weight was less. A cylinder, weighing 40. 135, was used to decompose dry ammonia for nine hours, and then weighed 40. 195, the increase being only 0.06 or 0. This accords with some expe riments made by M. Thenard. The properties of the iron are much changed by the operation, as has been observed; it is more brittle than before: but further, if left for an hour or two only in the heated gas, its grain differs from that of ordinary iron, and resem... bles that of steel; it may then, also, be hardened and tempered, n and will strike fire with flint like ordinary steel. If the action has continued for eight or ten hours, then the iron is not affected by ce the hardening process; it is softer than ordinary iron to the files has a grey black fracture, its grain partly resembling plumbago. The specific gravity of the wire before the operation was 7.788;. after, 7.6637.