It is further evident that admitting this law, all the numbers (p) in the column of barometric heights may be reduced to one standard number, as for example 30 inches, without at all changing the volume of V. Thus at 50° while one hundred and twenty volumes are absorbed under a pressure of 29.46 inches, one hundred and twenty volumes will also be absorbed at a pressure of 30 inches, the latter volumes being denser than the former in the proportion of 30 to 29-46.

The last column of the table represents the values of V, contained in column 6, after they have been reduced to the common temperature 60°. These numbers therefore indicate the relative quantities or weights of carbonic acid absorbed at the temperatures recorded.

175.7

The relation of the absorption to the tem- 147-9 perature is simply pictured in the accompa- 122-2 nying diagram, where the temperatures are measured in the horizontal, and the corresponding absorptions in 50-3 the vertical direction.

It will be remarked that this curve approaches the horizon

100.5

83-8

68.6
57.5

Fig. 2.

32 40 50 60 70 80 90 100

tal axis less rapidly, as the temperature rises, so that, for example, the absorption is greatly more diminished in passing from 40° to 60°, than in passing from 60° to 80°, and still more than in passing from 80° to 100°. This would lead to the inference that at temperatures much above 100°, we should find the absorption still quite considerable.

To satisfy ourselves on this point, we made repeated experiments at 150° and 2120, by passing a stream of gas from the pipe of the gasometer through a measured quantity of water, maintained by a peculiar lamp arrangement, at the proposed tempera

ture.

The pipe being withdrawn while the temperature was continued, any floating carbonic acid was removed from the surface of the liquid by a blast of air, and a solution of baryta was then added. In the water at 150°, a very copious precipitate was formed. This was separated by filtration under a vessel kept full of hydrogen gas to prevent the absorption of atmospheric carbonic acid by the precipitant, and the weight of the carbonate determined by the method of double filters.

By this procedure, 14.5 cubic inches of water at 150°, gave 3.51 grs. of carbonate of baryta, which corresponds to 11.4 volumes of carbonic acid gas for one hundred volumes of liquid.

In the water at 2120, a precipitate was also formed, but the amount although sufficient to produce a very obvious cloudiness, was too small to be readily estimated. We propose however to determine its quantity accurately hereafter. In this experiment the liquid was in active ebullition, while the stream of gas was passing, and continued to boil for a few seconds after the removal of the gas pipe.

It is thus clearly proved that water is capable of absorbing carbonic acid, in sensible quantity, while it is actually boiling under ordinary pressure. (To be continued.)

ART. XI.-Oxydation of the Diamond in the Liquid Way; by Prof. R. E. ROCERS and Prof. W. B. ROGERS, University of Virginia.

THE processes for oxydating the diamond, hitherto described, consist in actually burning this gem either in the open air, in oxygen gas, or in some substances rich in oxygen, as nitrate of potassa. In all these experiments a very elevated temperature is required. We have therefore been much interested by the discovery suggested to us by our experiments on graphite, but not completely verified until lately, that the diamond may be converted into carbonic acid in the liquid way and at a moderate heat, by the reaction of a mixture of bichromate of potassa and sulphuric acid, in other words, by the oxydating power of chromic acid.

The method of proceeding is much the same as in the oxydation of graphite, as described by us in the May number of this Journal; but the progress of the action is slower.

To succeed in the experiment, it is necessary to reduce the chips of diamond to a very fine powder, by trituration with repeated portions of pure siliceous sand in an agate mortar. A single grain weight of the gem will suffice for several experiments. In our repeated trials we have generally used less than half a grain, and we have obtained unequivocal proof of oxydation, by the evolved carbonic acid, when using less than ths of a grain.

The apparatus employed, is in the main, identical with that used in the analysis of graphite, but the Liebig tube is in this case replaced by a vessel containing lime water.

Precautions are necessary to correct a slight error arising from the evolution of a minute amount of carbonic acid from the bichromate and sulphuric acid, caused by the presence of a trace of organic matter or of carbonate in the former.

Operating on half a grain of diamond, we have in a first process obtained half a grain of carbonate of lime, and using the residuary matter have continued the oxydation, until at length the amount of carbonic acid evolved approached nearly to that due to the entire weight of the diamond. In these experiments, the carbonic acid evolved by the bichromate and sulphuric acid is first expelled from the apparatus, by a particular mode of conducting the operation.

SCIENTIFIC INTELLIGENCE.

I. CHEMISTRY AND PHYSICS.

1. Researches on the Latent and Specific Heat of Bodies; by C. C. PERSON, (Compt. Rendus, t. xxiii, p. 162; Pogg. Annalen, lxx, p. 300.) -Person gives the following as his results on latent heat :

If we examine this and the following table, we see that the latent heats do not follow the order of the temperature, and that they are not, also, inversely as the atomic weights, as was supposed. But they are related to the fusing points and specific heats as

(160+1)=7,

where t is the fusing point, 7 the latent heat, and the difference between the specific heats in the solid and liquid form. This relation may be expressed by the following proposition :-To obtain the latent heat, the difference between the two specific heats must be multiplied by the number of degrees between – 160° Cent. and the melting point. The latent heats calculated by this formula agree pretty well with those observed.

The following are his results on specific heat :

This table of the specific heats shews that they are nearly the same in the solid and liquid form for metals. The differences belong to the classes of those produced by change of temperature, and not by a change of the state of aggregation. This equality appears at first sight to upset his formula; but in reality it does not do so, if we consider the formula in its physical sense, and not as an empirical one.

2. Note on the means of testing the comparative value of Astringent Substances for the purpose of Tanning; by ROBERT WARINGTON, Esq., (Phil. Mag., xxxi, 150, from the Proceedings of the Chemical Society.)Having been frequently called upon to examine the value of astringent substances imported into this country for the purposes of tanning, such as valonia, divi-divi, sumac, cutch, &c., I am induced to believe that the detail of the manipulation adopted may not be without interest to some of the members of the Society. As the manufacture of leather was the object of the purchaser of these materials, gelatin was selected as the basis for the estimation of their comparative value; and after several trials with various kinds of natural and manufactured gelatin, such as varieties of isinglass, glue, patent gelatin, &c., the finest long staple isinglass was found to be the most constant in its quality and least liable to undergo change.

With this therefore the test solution was prepared, of such a strength, that each division, by measure in the ordinary alkalimeter tube, should be equivalent to the one-tenth or one-fourth of a grain of pure tannin, and thus the number of divisions used would indicate the proportion of available tannin or substance precipitable by gelatin contained in any specimen. A given weight of the sample under trial was then infused in water, or if necessary the astringent matter extracted by boiling, and the clear liquid precipitated by the test solution until no further deposit occurred.

It was necessary in the course of this operation to test at intervals a portion of the solution under examination, to ascertain the progress of the trial; and this, from the nature of the precipitate, was attended at first with some little difficulty: paper filters were inadmissible from the quantity of the solution they would absorb, and thus introduce a source of extensive error; subsidence rendered the operation very tedious. The plan I have adopted is as follows:-a piece of glass tubing, about twelve inches in length and about half an inch internal diameter, is selected, and this has a small piece of wet sponge loosely introduced into its lower extremity, and when it is wished to abstract a part of the fluid under investigation for a separate testing, this is immersed a few seconds in the partially precipitated solution; the clear liquid then filters by ascent through the sponge into the tube, and is to be decanted from its other extremity into a test glass; if on adding a drop of the gelatin solution to this a fresh precipitate is caused, the whole is returned to the original bulk, and the process proceeded in, and so on, until the operation is perfected; this method of operating is facilitated by conducting the examination in a deep glass. After a few trials the manipulation will be found extremely easy, and in this way considerable accuracy may be arrived at.

3. On the Manufacture of pure Sulphuric Acid; by AUG. A. HAYES, M.D., Assayer to the State of Massachusetts, (communicated for this Journal.)-In the arts, the rapid extension given to refined operations, has led to the consumption of pure chemical products. Applications of such substances as were formerly only in the hands of accurate chemists, are now of daily occurrence in manufacturing. The want felt for pure sulphuric acid, has to a certain extent been supplied by the Nordhausen acid; but aside from a higher price restricting its consumption, the manufacture is foreign to this country.

Without entering into scientific details, I shall describe an economical process which I have carefully studied and by which the pure acid, used in my laboratory, has long been obtained.

In the manufactories of sulphuric acid, the weaker acid from the lead chambers is concentrated in lead pans, usually to the density of 1-76, and transferred without cooling to the platinum alembics for fur ther concentration.

The modification commences with the hot acid, and it may be supposed to contain sulphurous acid, hydrochloric acid, hyponitric acid, arsenous acid, oxyds of iron and lead, alumina, lime, soda and organic matter, although the acid obtained from the combustion of Sicily sulphur, is rarely thus impure. On adding to the hot acid sufficient nitrate of potash, or soda, to destroy the organic matter, the brown SECOND SERIES, Vol. VI, No. 16.—July, 1848.

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