atomic arrangement, most of its oxygen combining with one half of the other elements to form an acid which unites with the potash.

It may be said, that if this explanation of the saponification of spermaceti be true, we should apply the same to the saponification of all fats, no longer considering them composed of acids and glycerine, but simply of carbon, hydrogen, and oxygen, in the proper proportions to form them. But there appears to me no necessity for forming such a conclusion, as the circumstances attending the saponification of spermaceti and that of the fats differ considerably, and if this difference be taken into consideration with what follows, there is no doubt that the justice of this explanation will be seen.

Another reason for supposing that spermaceti does not consist of an acid and a base, or rather that athal does not exist in it ready formed is, that in the products afforded by the distillation of spermaceti, no trace of athal is to be found. This fact is one that should be considered of great value in establishing the nature of spermaceti, for there is no way of explaining the non-existence of athal among the products of the distillation, except by admitting that the substance distilled did not contain it, for athal is a body easily volatilized without decomposition.

If, on the contrary, we remark the action of a strong solution of potash upon spermaceti at 100°, we find athal to be volatilized during the process, an evidence of the ease with which this substance is volatilized, as well as the necessity of an alkali for its formation.

Let us compare with this the action of heat upon the fats, with reference to the change that the glycerine undergoes. We find that if a fat be distilled, a portion of the glycerine is decomposed, giving rise to acroleine (a mixture of ascetic acid, &c.), and another portion passes over undecomposed; this is also exactly what takes place if glycerine be distilled alone, whereas in the distillation of spermaceti, its athal (supposing it to contain it) undergoes complete decomposition, although athal, distilled by itself, does not undergo the least decomposition.

This second reason then serves to increase the difference between the nature of spermaceti and that of the fats: but I am able to advance another fact stronger than either of the above, augmenting this difference.

Dumas and Stass have shown, that if athal be acted upon by potash at a temperature of from 410° to 428° Fah., an acid is the result, which acid they called athalic acid, the same that has been shown to result from the saponification of spermaceti, where the same alkali was employed, but at a much lower temperature. The action then of potash upon spermaceti, assisted by the proper temperatures, is to produce but one body, athalic acid, which circumstance would hardly take place were spermaceti composed of two or more proximate principles. We have no similar example among the fats.

Although cholesterine does not undergo any change by the action of a solution of potash at 212° Fah., still the analogy between

it and the spermaceti may exist, for it must be observed that cholesterine, having an atomic weight of more than one half of that of spermaceti, containing only one atom of oxygen, and not sufficient to give rise to an acid without the aid of an additional quantity, and it is probable that if cholesterine be treated with an alkali at a high temperature, that an acid similar to athalic acid would be the result, for then oxygen would be furnished from the water of the hydrated alkali.

For the above reasons, spermaceti should be considered a simple organic substance, having, as already shown, for its composition C4H6404 The action of an alkali upon it, produces a decomposition, which may be represented thus:

Under the head of the distillation of spermaceti, the decomposition brought about by the action of heat was shown to be represented thus:

Having made mention of the oxidation of spermaceti, as one of the evidences of the non-existence of oleic acid in this substance, I shall give a short statement of what has been done under this head, although but little, owing to the difficulty of isolating the products that are formed.

When nitric acid and spermaceti are heated together, a gentle action takes place, and nitrous acid fumes are given off; at the end of three or four days, the spermaceti still floats upon the surface of the acid, but considerably changed in its nature, having nearly the consistency of hog's lard, and an odour of rancid butter, owing probably to the presence of phocenic or butyric acid, but I am more inclined to believe phocenic acid, as this acid is found in the oil in connection with which spermaceti is found in its natural state, and the spermaceti may no doubt play some part in its formation: this fact is interesting, and worthy of future examination.

The action of the acid being continued (renewing it as it evapo

rates), in about ten days the spermaceti is in complete solution when the liquid is hot, and at the expiration of eighteen or twenty days the oxidation is completed, and if the solution be concentrated, a crystalline deposit takes place.

The examination of the products formed is as yet imperfect: the following is all that has been done that can be relied upon as

accurate.

After the completion of the oxidation, the mass was thrown upon a funnel, containing in its neck a bit of asbestos; the fluid was thus separated from the crystalline deposit, which was washed with strong nitric acid. The fluid that passed through, upon concentration furnished more of the same crystals.

The crystalline mass in the funnel gave, upon examination, no traces of suberic acid, but when dissolved in warm water and allowed to cool, a deposit took place, having the form of little grains, and the appearance of starch. Its reaction is strongly acid, and when crystallized several times from its aqueous solution, and dried at 212° Fah., it has a melting point of 298° Fah. It sublimes easily in feather-formed crystals; its ammoniacal salt does not precipitate the chlorides of lime, of baryta, or of strontia, the sulphate of copper, sulphate of zinc, or neutral acetate of lead. With the basic acetate of lead a precipitate is formed, which is soluble in an excess of the lead salt.

0-3645 gram. of this acid, burned with the bioxide of copper, gave 0.666 carbonic acid, and 0.230 water:

The silver salt is easily formed by double decomposition with the ammoniacal salt and nitrate of silver. It is slightly soluble in water, and not easily altered by the action of light.

Experiment 1. 0·525 gram. of this salt when burnt gave 0·294 gram. silver.

Exp. 2. 0612 gram. of this salt when burnt gave 0.343 gram. silver.

These give in 100 parts

1. 5601 silver, or 60·00 oxide of silver.
2. 56.05 66

60.19

Burnt with the bioxide of copper:

Exp. 1. 0-708 gram. silver salt gave 0.582 gram. carbonic acid, and 0.174 gram. water.

Exp. 2. 0.787 gram. of silver salt gave 0.6465 gram. carbonic acid, and 0.190 gram. water.

Out of this, the following formula of a bibasic salt is calculated.

This formula agrees with that of adipinate of silver, as made out by Bromeis, with an unimportant difference of one atom of hydrogen, and its physical properties and reactions are the same as adipinic acid: I consider it as such.

None of the other acids afforded by the oxidation of spermaceti have been obtained in a state of sufficient purity to be examined. There is, however, one among them, whose copper and zinc salts are more soluble in cold than in warm water, and if a solution of either of them be heated a precipitate is formed, which redissolves upon cooling; this phenomenon is most striking in the zinc salt. Those portions of the examination of this subject that are yet incomplete, I propose finishing at some future time.

Paris, April 29, 1842.

Thermography. By ROBERT HUNT, Esq., Sec. to the Royal Cornwall Polytechnic Society, &c.

THE Journal of the Academy of Sciences of Paris, for the 18th of July, 1842, contains a communication made by M. Regnault from M. Moser, of Konigsberg, "Sur la formation des images Daguerriennes ;"* in which he announces the fact, that "when two bodies are sufficiently near they impress their images upon each other." The Journal of the 29th of August, contains a second communication from M. Moser, in which the results of his researches are summed up in twenty-six paragraphs. From these I select the following, which alone are to be considered on the present occasion. "9. All bodies radiate light even in complete darkness. "10. This light does not appear to be allied to phosphorescence,

Comptes Rendus, tome xv, No. 3, folio 119.

for there is no difference perceived whether the bodies have been long in the dark, or whether they have been just exposed to daylight, or even to direct solar light.

10. Two bodies constantly impress their images on each other, even in complete darkness.

"14. However, for the image to be appreciable it is necessary, because of the divergence of the rays, that the distance of the bodies should not be very considerable.

"15. To render the image visible, the vapour of water, mercury iodine, &c., may be used.

"There exists latent light as well as latent heat."

The announcement at the last meeting of the British Association of these discoveries, naturally excited a more than ordinary degree of interest. A discovery of this kind, changing, as it does, the features, not only of the theories of light adopted by philosophers, but also the commonly received opinions of mankind, was more calculated to awaken attention than any thing which has been brought before the public since the publication of Daguerre's beautiful photographic process. Having instituted a series of experiments, the results of which appear to prove that these phenomena are not produced by latent light, I am desirous of recording them.

I would not be understood as denying the absorption of light by bodies, of this I think we have abundant proof, and it is a matter well deserving attention. If we pluck a nasturtium when the sun is shining brightly on the flower, and carry it into a dark room, we shall still be enabled to see it by the light which it emits.

The human hand will sometimes exhibit the same phenomenon, and many other instances might be adduced in proof of the absorption of light; and I believe, indeed, of the principle that light is latent in bodies. I have only to show that the conclusions of M. Moser have been formed somewhat hastily, being led, no doubt, by the striking similarity which exists between the effects produced on the Daguerreotype plates under the influence of light, and by the juxtaposition of bodies in the dark, to consider them as the work of the same element.

1. Dr. Draper, in the "Philosophical Magazine," for September, 1840, mentions a fact which has been long known, " That if a piece of very cold clear glass, or what is better, a cold polished metallic reflector, has a little object, such as a piece of metal, laid on it, and the surface be breathed over once, the object being then carefully removed, as often as you breathe again on the surface a spectral image of it may be seen, and this singular phenomenon may be exhibited for many days after the first trial is made." Several other similar experiments are mentioned, all of them going to show that some mysterious molecular change has taken place on the metallic surface, which occasions it to condense vapours unequally.

2. On repeating this simple experiment, I find that it is necessary for the production of a good effect, to use dissimilar metals; for instance, a piece of gold or platina on a plate of copper or of