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from one medium into another of a different density, and that the degree of refraction is in a direct ratio to the density of the body if incombustible, but increasing in proportion to the combustibility of the body through which it passes. Hence Newton divined the combustibility of the diamond, and the existence of a combustible principle in water.
If two substances be mixed together, the proportion of whose refracting powers is known, and regard be paid to the density of the mixture, we shall be thereby enabled to calculate the total refraction; and reciprocally, when the refraction of a mixture is asce: tained, of which the elements are known, we may, in like manner, calculate the proportional refracting power of each. M. Biot having applied this principle to mixtures of known proportions, and having found it just, afterwards applied it to ascertain the unknown proportions of other mix
By this experiment atmospheric air gave exactly that degree of refraction which ought to be produced, according to calculation, by a mixture of 0,21 oxygen, 0,787 azot, and 0,003 of carbonic acid. Even when these gases were not in the state of a simple mixture, but brought into the most intimate combination with each other, the same principle was found equally applicable, provided no very considerable condensation had been produced. Ammoniacal gas produced the effect indicated by the quantities of azot and hydrogen, which enter into its com position; but when too much condensed, some alteration, though very trifling, was observable; the same circumstance occurred in the experiment with water.
An accurate examination of the muriatic acid gas, according to these principles, fully demonstrated that its radical could not be azot, and consequently that this gas cannot be considered, as has been lately supposed, an oxyde of hydrogen containing less oxygen than water.
The refractive property of the dia mond being much greater than that of charcoal, the refractions of the carbonic acid, alcohol, ether, and other substances, of which carbon forms a part, M. Biot concludes that the diamond cannot be a pure charcoal, and that a fourth part of hydrogen, at least, is necessary, in order to render it conformable to the results of the experiment.
For this purpose it is sufficient to fill a glass prisin, under a known pressure, with the substance we wish to examine, or if it be a solid body, to form it into a prism itself, and observe through it a distant object. The angle of refraction is measured by the repeating circle, taking into account the weight, the temperature, and the humidity of the external air; and this method being susceptible of a degree of precision equal to that of astronomical processes, necessarily sur- The matters produced by organized passes in accuracy all the chemical means beings have not hitherto been examined employed with the same intention. But with sufficient accuracy. For although it will readily be perceived that this mode we have a general knowledge of the cleis only applicable to transparent sub-ments of which they are composed, and stances, and the principles of which, as far as regards their species, are known to
M. Cuvier next proceeds to point out the great utility of this discovery, and informs the Institute that the author has already applied it to the analysis of gaseous bodies, and obtained by this means the most important results, of which the following are among the most interesting:
At an equal degree of density, oxygen possesses the least, and hydrogen the greatest refractive power among all the gaseous bodies. The refractive powers of the same gas is in an acurate proportion to its density, under an unitorm temperature. It is to the presence of hydrogen, in particular, that substances possessing a high degree of refracting power appear to owe this property, since it was found to be present in all of them.
that these primitive elements are not very numerous, yet their combinations are so various, and they are so easily changed and converted in the course of the experiment, that it is necessary to study these combinations themselves as if they were simple substances. These matters considered under this point of view, are termed the immediate principles of organized bodies; and during the present year several of them, we learn from M. Cuvier, have been discovered by different French chemists. Among others he mentions M. Vauquelin and Robiquet, who have found in the sap of asparagus, a crystaline matter, soluble in water, which is, however, neither an acid, nor a neutral salt, and which is not neted upon by the usund re-agents. These cele brated chemists propose to follow out the investigation of this substance, and in due time to lay the result of their labours
before the Institute. In the same class may be ranked, proceeds the Reporter, the discovery of a saccharine principle in the bile, by M. Thenard, Professor in the College of France. This principle, which was before only suspected to exist, has been clearly demonstrated by the learned Professor, who has shewn that it possesses the property of holding the oil of the bile in solution. The means of analysis employed by M. Thenard has been mentioned, by the commissioners empower ed by the Institute to examine his labours, as being singularly ingenious; and it is, in fact, extremely difficult entirely to free this substance from those with which it is intermixed.
Some recent researches respecting the nature of coffee by M. Seguin is next noticed by M. Cavier. From the result of those experiments, it would appcar that this grain is composed of albumien, oil, a peculiar principle, which the author denominates the bitter principle, and a green matter, which is a combination of albumen and the bitter principle; that the proportions of those principles vary in different kinds of coffee; that torrefaction, or roasting, as it is termed, aug ments the proportion of the bitter principle, by destroying the albumen; that these two last principles contain inuch azot, and that the bitter principle is autiseptic. The oil of coffee is inodorous, coagulated, and of a white colour, like hog's lard.
M. Seguin next extended his researches to other vegetables, and discovered that a great number which he has specified contain albumen, and also a certain portion of the bitter principle, more or fess similar to that of coffee.
This remarkable quantity of albumen being more particularly found in the juices of those vegetables which ferment without the aid of yeast, and yield a vinous liquor, as the juice of raisins, gooseberries, &c. M. Seguin endeavoured to discover whether albumen might not contribute to produce this intestine motion hitherto so little understood; and we are informed that having separated the albumen from these juices, they becaine meapable of fermentation, but on. uniting albumen with them artificially, as that of the white of an egg, for example, or of saccharine matter, fermentation took place, when the other necessury circumstances concurred, in which case a matter similar to yeast was unifomaly deposited, which appea.ed to be
only albumen changed, and become nearly insoluble without its fermentable quality being destroyed; from which he concludes that albumen, whether animal or vegetable, is the real fermentative principle. In the course of his investigation, M. Seguin also discovered that albumen exists in three different degrees of insolubility, and possesses a greater or less aptitude to become fibrous; that its action. is in proportion to its solubility; that the respective proportion of albumen and sugar present in the different juices determines the vinous or acetic nature of the product of the fermentation; that the liquor thus obtained is more spirituous in proportion to the greater quantity of sugar; and, in short, that most fermentable juices contain a bitter principle analogous to that of coffee, which, though it does not assist in the fermentation, nevertheless contributes towards the taste and preservation of the fermented liquor.
Tannin, formerly discovered by M. Seguin, and the character of which is to form an insoluble compound with gela tin, has, we are informed by M. Cuvier, been lately re-examined by Bouillon la Grange, professor in the Lyceum.
He found it also to possess an affinity for the alkalies, for earths, and for inetallic oxydes, and that it might be converted into gallic acid by absorbing oxygen.
The tannins extracted from different vegetables vary somewhat in their composition; and that which Mr. Hatchett discovered in great abundance in the caoutchouc contained a greater proportion of oxygen than others.
Mr. Hatchett is of opinion that tannin may be artificially formed, by treating charcoal with the nitric acid.
The next discovery noticed by M. Cuvier is that by M. Morichani, an Italian chemist, who having found the fluoric acid in the enamel of the fossile jawbones of the elephant, was led by this circumstance to analyse the enamel of the human teeth, and is of opinion that it contains the same principle, GayLussac has also found it in recent, as well as fossile ivory, and in the tusks of the wild boar.
Messrs. Fourcroy and Vauquelin, on repeating these experiments, obtained this acid not only from the tusks, but from the teeth which had undergone a change by having remained long under grounds but they failed a procuring it
from the same parts in a recent, or even in a fossile state, unless they had undergone such a change.
M. Vauquelin. has also been engaged, during the present year, in conducting a series of accurate and interesting experiments on hair. By dissolving it in water by means of Papin's digester, and afterwards examining the solution and its residuum, he succeeded in extracting nine different substances; an animal matter similar to mucilage, two kinds of oil, iron in a peculiar state, some particles of oxyde of manganese, phosphate and a small portion of carbonate of lime, a considerable portion of silica, and much sulphur. Black hair yielded an oil of the same colour, while red hair produced a reddish-coloured oil, and white one wholly colourless. The last contained always an excess of sulphur, and the white, in particular, magnesian phosphate.
Besides these theoretical researches, chemical principles have been applied to many useful practical purposes; among which M. Cuvier mentions a mode of imitating Roman alum, discovered towards the conclusion of the former year, and which has succeeded so completely that the alum manufactured in this manner is sold at the same price as the genuine Roman alum. This method merely consists in calcining and re-crystallizing the common alum, in order to deprive it of its super-abundant acid. M. Curaudeau contends, however, that it is also necessary to oxygenize the small portion of iron usually contained in alum, to its maximum. But a memoir lately published by Messrs. Thenard and Board has perfectly cleared up this subject; from this we learn that a thousandth part of iron will sensibly influence the effects of alum as a mordant; and it is to deprive it even of this small quantity to which the efforts of our manufacturers ought chiefly to be directed.
The oxygenation of the iron appears extremely well calculated to answer this intention, since it renders it insoluble in the acid.
The application of the oxygenated muriatic acid gas to the destruction or correction of contagious miasmata, has, we are informed by M. Cuvier, been much extended during the present year, and its beneficial effects confirmed by various extensive trials. M. Desgennettes has, in particular, constantly employed it in the Military Hospital of Val-de-Grace; and he has transmitted to the Institute
a comparative view of the cases in which these fumigations not only prevented the communication of the disease, but appeared to assist in their cure when actually produced.
M. Pinel has experienced similar success by the employment of the same means in the Hospital of Salpetriere; and the beneficial effects resulting from its use in Madrid, as well as in other places in Spain, have already been made known to the public through the medium of different Spanish Journals.
We next learn from M. Cuvier's report that he himself was led by his experiments on the fossile grinders of elephants to examine others in a recent state; and an occasion having presented itself in the course of a few years of dissecting two elephants, nearly full grown, he was by that means enabled to observe with greater precision the growth of the teeth in these animals, and thence to deduce conclusions respecting dentition in general. The anatomy of large animals, be observes, may justly be considered as a kind of natural inicroscope, which assists in dscovering that of the smaller kind. It was with a view to confirm the doctrine of the late John Hunter, that M. Cuvier was induced to enter into this investigation, at least so far as regards the osseous portion of the teeth. It is not furnished with vessels, nor formed by intus-susception, like true bones, but by a successive transudation of layers produced by the pulp of the teeth, and which lie over each other. The enamel is deposited above by the membrane which envelops the young tooth, and is attached to it by a species of crystallization; in fine, a third substauce, peculiar to some herbivorous animals, is deposited after the enamel, but by the same membrane, which changes its nature at a certain period.
This third substance was first discovered by M. Tenon, who has termed it the osseous cortex, but who conceives it to be formed by the ossification of the capsular membrane. This intelligent anatomist, M. Cuvier informs us, has comm nicated to the Institute, during the present year, the results of some well-devised experiments on the teeth of the cachalot, and on those of the crocodile, from which it appears that the first hvo no enamel, but only an osseous cortex, They are easily distinguished from each other, because the cummel is much harder, and dissolves entirely in acids, without leaving any gelatinous parenchy
ma. Neither the tusks of the elephant, nor the grinders of the morse and the dugong, have any other covering.
From this Report we farther learn that M. Tenon has presented to the Institute a work on this subject, in which he has been engaged for more than twenty-five years, and wherein he had anticipated M. Cuvier himself, as well as Mr. Everard Home, and other British anatomists, in most of their observations on the manner in which the teeth of elephants decay, and are replaced.
The same indefatigable anatomist has at present nearly ready for publication a work on the Diseases of the Eye, from which it appears that he has made several new and interesting observations on the parts connected with that organ.
M. Cuvier concludes his Report by announcing the re-publication of several valuable works, and among others, a new edition of Dumas' Physiology, and M. Barthé's Elements of the Science of Man,
LIST OF NEW PUBLICATIONS IN MAY.
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