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with a little more carbon, and a certain quantity of oxygen and hydrogen in the proportions to constitute water, would return to an essential oil.

Gehlen rejected this theory for good reasons*. Having observed that in passing muriatic acid through the essential oil of turpentine, no gas was disengaged; that only a certain portion of the oil was converted into white crystals having the appearance of camphor, and that the remainder appeared as a brownish-black liquid of great acidity; that the crys tals too as well as the liquid contained muriatic acid in intimate combination, &c. he has concluded, that in this operation the essential oil of turpentine is decomposed, that the greatest part of its hydrogen combines with a small quantity of its carbon, and with a certain portion of muriatic acid, to form concrete camphor, whilst the other principles of the oil combine with the remaining portion of muriatic acid to form the brownish-black liquid; therefore that this liquid contains more carbon and less hydrogen than the camphorie concre tion; and that, in the formation of both, the muriatic acid acts only by the tendency it has of uniting to them, and not, as the chemists above quoted say, by forming a certain quantity of water at the expense of the principals of the essential oil.

I repeated and varied with great care the experiments on the essence of turpentine and muriatic acid, made by Kind, Tromsdorff, &c., and above all by Gehlen. I obtained the following results: 100 grammes of essence of turpentine purified by distillation, and plunged into a freezing mixture of ice and salt, absorbed 30 grammes of muriatic acid gas; no gas but muriatic escapes, which perhaps was not entirely absorbed at first, or passed through the liquid when the operation was nearly finished. The essential oil is converted into a soft and crystalline mass, from which, during its desiccation for three days, may be separated 20 grammes of a liquid that contains many crystals and nearly 100 grammes of a white substance, granular, crystaline, volatile, and having a strong smell of camphor. This substance quickly loses, by exposure to the air, the property which it at first has of reddening turnsole paper, and afterwards only very minute quantities of acid can be separated from it, even by warm alkaline solutions. Yet when it is sublimed, the vessels in which the operation is made become strongly acid; and when, instead of subliming it, it is passed through a red-hot iron tube, a

Vide Journal de Gehlen, tome vi. p. 458.

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greater quantity of acid is still abstracted from it. Lastly, when decomposed both by concentrated and weak nitric acid, a large quantity of oxy-muriatic acid is produced in the first instance, and in the second much muriatic acid. Relative to that portion of liquid derived from the crystalline mass, the weight of which was 20 grammnes, it was white, and diffused acid vapours, but ceased after an exposure of some days to the atmosphere, and was no longer acid; it crystallized in mass some degrees below zero, and preserved an intimate union with much muriatic acid.

Thus all my observations, except one only, agree with those of Gellen. That in which we do not coincide is relative to the liquid product of the operation. Gehlen obtained it of a brownish-black, and I always obtained it white. This difference, I think, depends on Gehlen having used the essence known in commerce, which contains, unless distilled with great care, a resin, and has then the property of blackening and forming a large uncrystallizable residue. Neither do I draw from my observations the same theoretical in ferences as this chemist does from his. I think that the es sential oil of turpentine is not decomposed by muriatic acid, and consequently that these two bodies combined together in certain proportions form concrete camphor; probably the small portion of liquid product obtained by him is of the same formation; besides, it is not improbable that the dif ference existing between the camphoric concretion and the liquid product, depends on a small quantity of an ethereal oil mixed with the essence, and capable of forming with mu riatic acid a liquid product. Lastly, what induces me to believe that the muriatic acid does not decompose the essence, but, on the contrary, combines with it, is, that this acid evidently combines with all the principles of alcohol without affording many different products, and that alcohol is a bydrogenous body as well as the essential oil of turpentine. Yet whatever it may be, nothing is more certain than that this combination has the greatest resemblance to native camphor.

Perhaps the camphor which is extracted from the essential oils of plants, particularly from that of lavender, is a combi nation of essence and acid alone; perhaps too the camphor of commerce, or the camphor of the laurel, which does not appear to contain any mineral acid, (for none can be obtained from it by destructive distillation,) is formed of an essential oil and vegetable acid alone. These views, as they are founded on facts, at least deserve some attention, and, if confirmed by experience, may probably be of great advantage.

I have

I have likewise formed the combinations of the essence of lemon and of lavender with muriatic acid. 32 grammes of the essence of lavender require 22 of acid; the resulting com pound is blackish, acid and liquid. 26 grammies of the essence of lemon absorb 22 grammes of acid; the essence is of a brownish hue and solid. Neither of these essences had been purified; but both were used in the state they are generally found in commerce.

The essential are not the only oils capable of combining with acids. It has long been remarked that the fat oils form with different acids peculiar kinds of soap. The sulphuric acid when concentrated has this effect upon all of them; it produces with the oil of olives in particular a soapy matter, of a thick and greenish appearance, which gradually acquires consistence; when washed with water it becomes white; it is acid, but less so than if the acid was uncombined, and it may be brought into the neutral state by a proper quantity of potash.

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Tannin besides, which is a vegetable matter, contracts, as is well known, a strong union with acids; for the concentrated sulphuric acid suddenly precipitates it from its solution in water, and I am convinced that however often the precipitate may be washed, it is always acid. Nature itself has offered us a compound of this species. In fact, I have treated 10 grammes of gallnuts with 2 litres of boiling water, and although the residue, had been washed with two litres more of very warm water, it still strongly reddened tincture of turnsole in the gallnuts therefore, the gallic acid is retained by a true affinity. But as the quantity of gallic acid abstracted by a spontaneous decomposition far exceeds the quantity of free acid existing in its natural state, we must conclude that the greatest part of the acid is certainly neutralized by the tannin. It is observed too, that if a decoction of gallnuts be allowed to follow its own course, as the tannin is destroyed, the liquor becomes more and more acid. One may, indeed, attribute this phænomenon to the transformation of the tannin itself into gallic acid; but numberless observations authorize us to believe that this is not the case.

1. That vegetable substances during their decomposition form no other acid but the acetic.

2. That gallnuts evidently contain abundance of gallic acid, and that, this acid having a strong affinity for tannin, the two bodies should necessarily neutralize each other in part.

3. Because there are many remarkable instances of the power of some vegetable substances to neutralize acids. 4. Lastly,

4. Lastly, that tannin precipitated from a decoction of gallnuts by an alkali or carbonate of ammonia, contains, according to my experiments, a good deal of gallic acid as well as a small portion of saline base. The proof I have of this is, that it produces with almost all the metallic solutions the same effects as gallic acid, or gallate of potash. Thus it gives red precipitates with solations of the peroxides of mer cury, blackish gray with solutions of peroxides of iron, a blue one to those less oxidized, the colour of wine lees (lie de vin) to those least oxidized. It follows then that we are not yet acquainted with the pure tannin of gallnuts, and of most other substances, and consequently that we know not how to act with them on metallic solutions, &c. Inquiries which have this object in view cannot but be interesting; and I propose to pursue them, in as much as they will on some future day allow me to bring forward the question I am now treating of.

1

If, after having examined the vegetable substances which readily combine with acids, a search is made among animal substances endowed with the same properties, five will evidently occur: curdy matter, albumen, picromel, gelatin, and urea. This property is generally found in the curdy matter, as it is known that acids coagulate milk, that the coagulum contains an acid, and that this acid is even sensible to turnsole paper. Of course the affinity between those two bodies is well marked; yet it is not sufficiently strong to destroy all doubts to the contrary; for I am satisfied that the excess, and perhaps also the whole, of the acid may be ab stracted by means of a large quantity of water.

If water alone be sufficient to take the acid from the curdy matter, it fails to produce the same effect when the acid is united to albumen; for the washings may be continued to an unlimited extent, and there will be always found acid undis solved.

We must conclude therefore, that this animal substance exerts on acids a more powerful attraction than the curdy matter; but this action varies in itself according to the con centrated state of the acid. As the acid is saturated with water, the results are combinations more or less insoluble, and which again dissolve, the acid being saturated with ammonia, or with either of the other alkalis, and in which albumen is nowise altered. If on the contrary the acid is very strong and con centrated, the precipitates formed will always be acid, but will contain albumen in the state in which it exists when concreted by fire: this has appeared in treating the precipitates with a weak solution of ammonia. In the first instance, the

solution

solution will be gradually formed and complete; in the second, the acid alone will be taken up, and the albumen will remain undissolved in the form of a thick magma.

The combination of picromel with the acids took place with the same facility as with the preceding. Almost as soon as these substances come in contact, an acid precipitate is formed, which redissolves when neutralized. It is principally with the sulphuric, nitric, and muriatic acids that picromel forms slightly soluble compounds.

The concentrated nitric acid is the only one, according to Messrs. Fourcroy and Vauquelin, that precipitates urea from its solution in water; yet it is probable that the other acids are capable of combining with it; and if they do not precipitate it, it is because the compounds are soluble in water. I have observed that these combinations never form when the temperature is below 40 or 50, particularly with the sulphuric and muriatic acids; and that otherwise there is a disengagement of carbonic acid, and a production of a large quantity of ammonia.

*

Lastly, gelatin itself may unite with some acids, and principally with the oxy-muriatic acid. To effect this combination it is necessary to pass the gaseous acid through a solution of gelatin. In this operation the solution gradually becomes turpid and precipitates flakes, which unite together in the form of pearly filaments very elastic and flexible. These flakes have been considered by M. Bouillon-Lagrange, in a memoir upon the gizzard of birds, as the oxygenated gelatin but it is a mistake; they are really formed of gelatin slightly altered, and of the muriatic and oxy-muriatic acids. Their striking characteristics are, that they are insipid, insoluble both in water and alcohol, not liable to putrefy, slighty acid; though a sufficiently large portion of acid enters their composition to emit spontaneously for several days the oxy-muriatic acid gas, much more may be disengaged by means of lieat: lastly, they contain so much acid as to be soluble in alkalis, and to form with them muriates.

Thus we have examined five vegetable matters, and six animal matters, capable of an intimate union with acids. Three of the former, viz. alcohol, essential oil of turpentine, and a substance abounding in carbon, and produced from alcoliol decomposed by oxy-muriatic acid, neutralize acids equally as well as the strongest alkalis. The last seven form

* Annales de Chimie, tom. ivi. p. 24.

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