ric acid.

free phospho- failed to yield phosphoric acid: I was under the necessity therefore of adopting the synthetical method. Accordingly after having saturated by means of potash the extract of some urine, that I had evaporated to dryness with the precautions already described, I poured in a little vinegar, treated it with alcohol, and obtained the same results as I have already related; that is to say, the portion, that was not dissolved after repeated affusions of alcohol, was acid. This proof, I am aware, may still be questioned: for, if the phosphoric acid existed in the urine, it would be partly retained by the salts present in it, in the same manner as the acetous, and would become insoluble in alcohol. But if it be considered, that the existence of the acetous acid in urine appears certain*; that nothing demonstrates the presence of the phosphoric; that the greater part of the free acid of the urine evaporated to the consistence of a sirup dissolves in alcohol; and that all this acid, thus dissolved, is the acetous lastly, if we recollect, that the residuum is slightly acid; and that, if saturated with potash, afterward acidulated with vinegar, and treated afresh with alcohol, it remains equally acid: all these circumstances compared together, I conceive, will acquire such a degree of certainty, as absolutely to convince us, that it is the acetous acid alone in urine which dissolves the phosphate of lime, and which alone too most commonly imparts to it the property of reddening infusion of itmus,

Farther proof that it is the acetous only.

But, to render this last conclusion still more evident, I ought to demonstrate, more directly than has hitherto been done, that the benzoic acid is not in fact a constant principle of urine. For this, instead of employing sublimation with or without an excess of another acid, when the urine is reduced to a sirupy consistence; a method always inaccurate, since the benzoic acid combined with ammonia is car

I believe, that, in the evaporation of the urine in a water bath, a little uree is decomposed, and that ammonia, and perhaps a little acetous acid is formed. Supposing this to be the case, it still remains very probable, that the acid of urine is the acetous acid, and not any other: for in favour of this opinion I might not only adduce the reasons that have been, or that will be given, but even the tendency the uree would have in this case to be converted into acetous acid.

ried off more or less with the water that rises in vapour; I added me before I began the evaporation, and treated the extract with alcohol.

It is true by this method we dissolve, beside the benzoate of lime, some uree, muriate of ammonia, and soda, and acetous acid but if the alcoholic solution be converted into a concentrated aqueous solution, the acids added afterward will soon manifest the presence of benzoic acid, if there be ever so little in the solution.

lysing urine.

Thus, when we would analyse urine, the benzoic acid Mode of anashould be first sought for, either by this or some analogous process. If by this we discover no trace of it in the liquid, which is most commonly the case, we may conclude, that it does not contain any sensible quantity of it: then, after having evaporated another portion of the urine in a waterbath, and thus ascertained the quantity of water that enters into its composition, the residuum must be treated repeatedly with alcohol at 36°: thus we shall dissolve the urce, the muriate of ammonia, some muriate of soda, and the greater part of the acetous acid.

The mixture of these different substances should be divided into three portions. From the first the acetous acid is to be separated by the means pointed out. From the second the uree is to be extracted by concentrated nitric acid, from which again it is to be separated by the carbonate of potash and alcohol. Lastly, from the third part the quantity of sal ammoniac and muriate of soda is to be ascertained by sublimation. In this sublimation the uree is destroyed, the acetous acid is volatilized, the muriate of soda remains behind, and is to be weighed: the sal ammoniac sublimes, and is to be collected; and as it is always mixed with black matters, and may besides contain a little carbonate of ammonia, it is to be purified by dissolving it in water and evaporating the solution.

The matters contained in urine, that are soluble in alco Soluble mat

without the

Pure uree does not crystallize: it is only when combined with cer. Uree does not tain salts, which frequently happens, that it forms crystals I believe, crystallize but I am not certain, that it renders several salts soluble in alcohol, which when alone are insoluble in it. This might easily be verified with muriate of barytes.

addition of

some salt.

bol,

in urine.

ters contained hol, are five; namely, acetous acid, benzoic acid, muriate of ammonia, muriate of soda in part, and uree. Those that are insoluble in it are more numerous, as at least eight may be reckoned; namely, four phosphates, two sulphates, muriate of soda, aud uric acid. On treating with water these eight substances insoluble in alcohol, we dissolve the phosphates of soda and ammonia, a very little phosphate of magnesia, the muriate of soda, the sulphates of potash and soda, which are known by their crystallization, and which may be separated from one another in a certain degree by solutions of platina. We may judge that phosphate of magnesia is present by means of potash, which will precipitate a small quantity of this earth.

Milk quite

fresh contains

a free acid.

Probably the

acetous.

This proved,

The substances insoluble in water then are the phosphate of lime, some phosphate of magnesia combined with phosphate of ammonia, and uric acid, which may be separated in the usual way. This method however differs very little from those that have been given by other chemists; and I describe it here in a concise manner, because it is intimately connected with my subject.

PART III. Of the acid of milk.

Milk as soon as it comes from the mammary glands reddens litmus paper: it contains therefore a free acid. When I discovered this fact near eighteen months ago, I endea voured in vain to obtain it pure, in order to examine its properties and all my endeavours since that time, to attain the same object, have been equally fruitless.

Though every thing leads us to believe, that it is the acetous acid, yet it is the same with respect to it, as with respect to the acids of sweat and urine: to pronounce decidedly on its nature, it was necessary to separate it, and combine it afterward with salifiable bases. This at length I effected, by pursuing a method analogous to that, which enabled me to obtain the acid of urine. 1st, I evaporated the milk to dryness: 2dly, I treated the residuum with barytes water, to saturate the acid: 3dly, I evaporated to dryness again : 4thly, I treated it with alcohol, to dissolve in part the extractive matter, and particularly to collect the caseous substance, so that none should remain suspended in the water:

5thly, I macerated in water what was not dissolved by the alcohol, filtered the liquor, concentrated it by evaporation, and distilled it with phosphoric acid. By these means I collected in the receiver a fluid, which possessed all the properties of acetous acid.

clusions.

It follows then, from the various experiments I have de- General conscribed, 1st, that urine probably contains no free phosphoric acid; but that there is to be found in it, as well as in the milk and sweat, acetous acid. 2dly, That the sweat contains, beside this, a great deal of water, some muriate of soda, a small quantity of animal matter, and some traces of oxide of iron and phosphate of lime.

in several other

It is probable, that the acetous acid exists in several other Acetous acid substances. Several observations lead me to believe, that probably exists it would be found in cantharides: the analogy of the bombic substances, and formic acids with vinegar have already been suspected: and I would almost venture, to generalize this idea, and say, that it exists in almost all animals, as in the sap of almost perhaps in most animals. all vegetables: at least we may affirm, that of all the acids. its formation costs nature least; its principles having such a Most easily tendency to unite, that we can scarcely ever disturb the formed. equilibrium of the molecules of organized substances, without producing more or less of it. If the decomposition be rapid, acetous acid is formed; if slow, it is formed still: witness the distillation of vegetable and animal substances,; their treatment by nitric and by oxigenized muriatic acid, their spontaneous decomposition, and their transformation into vegetable mould or adipocire.

ries intended.

In cases of indigestion it is known, that the food becomes Formed in inacid, and this too is owing to acetous acid. In several cir- digestion. cumstances however, its production has not yet been thoroughly appreciated: it remains to be seen, whether it exist Farther inqui-" in the milk of all kinds of animals; whether it be found in the sweat of all, and whether the sweat of different animals be identical; and lastly, whether it be not in the state of acetate in such urine as is alkaline. This is an inquiry which I propose to undertake, and the results of which I shall submit to the judgment of the Institute, if they prove worthy

its attention.

Orpiment and realgar,

XIV,

Remarks on Orpiment and Realgar: by Mr. THENARD*.

ORPIMENT and realgar are two ores of arsenic suffi

ciently abundant. The first is almost always in the form of laminæ of a pure yellow colour; and the second is as genesaid to be the rally a red mass more or less brown. Bucquet asserted, that same sulphuret of arsenic mothese compounds were formed of oxide of arsenic, and suldified by heat; phur, in the same proportions, and ascribed their difference of colour to the different degree of heat employed in prethen sulphuret paring them. Bergman likewise admitted the oxide of arted oxides, differing in their senic, as well as sulphur, in both; but he imagined they proportions; differed in colour because they contained different propor

tions. These opinions, supported by some experiments that were capable of deceiving, prevented chemists for some time from forming a decided opinion: that of the Swedish chemist however prevailed, and since the creation of the new theory, and the reform of chemical language, orpiment and realgar are described in chemical treatises under the names of yellow sulphuret of oxide of arsenic, and red sulphuretand lastly ted oxide of arsenic. Nevertheless some have lately thought, sulphurets of that these two substances differed less with respect to their proportions of sulphur, than those of their oxigen.

different ox

ides.

Arguments for

nion.

Thus it has been successively supposed, 1st, that orpiment and realgar were homogeneal compounds containing burned arsenic: 2dly, that they were oxides more or less sulphuretted: and 3dly, that they were oxides more or less oxided, as well as more or less sulphuretted.

The partisans of the first opinion ground it on the fact, that by heating equal quantities of arsenious acid and sulphur in a less or greater degree the product is sometimes orpiment, at others realgar: therefore say they, if their colour differ, it is owing to the heat, which occasions a different arrangement of their particles.

Annales de Chimic, vol. LIX, p. 284, Sept. 1806. This paper was read to the Philomathic Society about a year ago.

Those