water, the whole of it is found in the first solution mixed with a little of the two other salts. The next solution consists chiefly of caproate, and the last of caprate of barytes as the least soluble salt of the three. By repeated crystallizations the butyrate of barytes is freed from the admixture of the other salts, and obtained in a state of purity. The butyrate of barytes is decomposed in a glass tube by means of phosphoric acid, and the barytic acid obtained precisely in the same way as the phocenic acid is obtained, and as the process was described in the last section.*

Class I.

Div. II.

Butyric acid thus prepared is a colourless liquid, which does Properties. not congeal though cooled down to 16°. It boils when heated a few degrees higher than 212°. At 50° its specific gravity is 0-9675. Its odour is analogous to that of acetic acid and rancid butter conjoined; somewhat similar to that of phocenic acid, but not so strong. It stains paper like oil, but the stain disappears by the evaporation of the acid. It has a strong acid taste, leaving an impression of sweetness. Like phocenic acid it whitens the part of the tongue to which it is applied.

Water dissolves it in all proportions. A solution of two parts acid in one part of water has a specific gravity of 1.00287. Alcohol of the specific gravity 0.794, dissolves it in all proportions. The solution has an etherial odour of pippins (pomme de reinette). Concentrated suphuric acid dissolves it at 60° with the evolution of heat. Cold nitric acid of the specific gravity 1-312, dissolves it also without any alteration. The solution has an etherial smell. When mixed with hog's-lard, it gives it an exact resemblance to butter. But when exposed to the air the acid gradually escapes, and the lard remains unaltered. Butyric acid burns like the volatile oils.

It combines with bases and forms a genus of salts called butyrates. The following table exhibits the constitution of several of these salts as analyzed by Chevreul.

The reader will find a detailed statement of the processes in Chevreul

sur les corps gras, p. 215.

The mean of these numbers gives 9-62 as the atomic weight of butyric acid.

Chevreul analyzed butyric acid by heating butyrate of lead with a sufficient quantity of oxide of copper. He found it Composition, resolvable into the following constituents,

History.

The number of atoms best agreeing with this constitution, and with the atomic weight deduced from the analysis of the butyrates, is the following,

Butyric acid in its ordinary state is composed, according to the analysis of Chevreul, of

Butyric acid.
Water

9.625

1.116

is obviously a compound of 1 atom acid and 1 atom water.

SECTION XXXI.—OF CAPROIC ACID.

This acid was discovered by Chevreul in 1818. It was named from capra, a goat, because it exists in the butter of the cow and goat.

Caproic acid is obtained in the state of caproate of barytes by the processes described in the last section. The 2d solution in the 277 of water consists chiefly of caproate of barytes, and it is to be freed from the small quantity of caprate of barytes which it contains by repeated crystallizations and solutions. One part of caproate of barytes is to be put into a glass tube with 0-2963 of sulphuric acid diluted with its own weight of Chevreul sur les corps gras, p. 115.

water. After 24 hours the caproic acid which has separated is to be drawn off. It is to be digested for 48 hours on its own weight of chloride of calcium and then distilled.

Class I.

Div. II,

Caproic acid is a colourless liquid, resembling a volatile oil Properties. in appearance. It does not congeal at 16°, and it may be distilled over without decomposition. At 79° its specific gravity is 0-922. Its taste is a sharp acid, leaving a sweetish impression on the palate. Its smell resembles that of weak acetic acid, or rather sweat. It whitens those parts of the tongue to which it is applied.

At the temperature of 45°, 100 parts of water dissolve 1.04 of caproic acid. But alcohol of the specific gravity 0·794, dissolves it in all proportions. It combines without decomposition with concentrated sulphuric acid, and with nitric acid of the specific gravity 1-312. It burns with flame like the volatile oils. It combines with bases, and forms a genus of salts called caproates. Chevreul analyzed several of these caproates, and obtained the following results:

The mean of these analyses gives as 13.75 for the atomic weight of caproic acid. It was analyzed by Chevreul by means of oxide of copper. He found the constituents to be

The atoms coming nearest to these numbers, and corresponding best with the atomic weight deduced from the analyses of the salts, are the following:

Composition.

13.25

1.147

Caproic acid, in its natural state, is a hydrate composed of

Caproic acid
Water

It is obviously, therefore, a compound of 1 atom acid and I

atom water.*

History.

Properties.

SECTION XXXII.—OF CAPRIC ACID.

This acid was discovered by Chevreul in 1818, at the same time with the caproic: and the name was also derived from capra, because, like the two preceding acids, it exists in the butter of the cow and the goat.

It exists in the aqueous solutions of butyrate of barytes, described in the two last sections, as dissolved in 2·77 water at different times. The greatest portion of the third solution consists of caprate of barytes. It is purified by repeated crystallizations and solutions. And the pure caprate of barytes may be either decomposed by means of phosphoric acid or sulphuric acid, in the way described in the two last sections.

Capric acid is solid, and has the shape of colourless needles at the temperature of 62°. At 64° it melts into a transparent colourless liquid resembling a volatile oil. Its specific gravity It has the smell

at 64° is 0·9103. Its taste is acid and hot.
of caproic acid with a slight odour of the goat.

It is very little soluble in water at the temperature of 68°, 1000 parts of water dissolving only one part of capric acid; but alcohol dissolves it in all proportions.

It forms a genus of salts called caprates, two of which were analyzed by Chevreul with the following results:

The mean of these two analyses gives 16:96 for the atomic

weight of capric acid.

* Chevreul sur les corps gras, p. 134.

This acid being analyzed in the usual manner by Chevreul, was found composed of

Class I.

Div. II.

The atoms corresponding best with these proportions, and Composition. approaching the atomic weight deduced from the salts, are the following:

But if 18.25 be the atomic weight of the acid, Chevreul's analyses of the caprate do not constitute very near approximations to the truth.*

SECTION XXXIII.-OF HIRCIC ACID.

This acid was discovered by Chevreul during his researches on fatty bodies. But its properties have been very imperfectly examined.

To obtain it soap made of mutton tallow is to be decomposed by tartaric or phosphoric acid. The aqueous liquid being distilled the hircic acid passes over with the water. Neutralize it with hydrate of barytes, evaporate to dryness, and decompose the hircate of barytes by sulphuric acid previously diluted with its own weight of water.

It is a colourless liquid which does not congeal at 32°. It Properties. is lighter than water; has a smell analogous to that of acetic acid. It is volatile, very little soluble in water, but very soluble

in alcohol. It reddens strongly litmus paper.

Hircate of potash is a deliquescent salt. Hircate of barytes

is not very soluble in water, and is composed of

Hircic acid
Barytes

12.21

9.5

According to this analysis the probable atomic weight of hircic acid is 12 or 12.25.+

SECTION XXXIV.- -OF RICINIC ACID.

This acid was discovered in 1827 by MM. Bussy and History. Lecanu. The method of obtaining it is as follows:

* Chevreul sur les corps gras, p. 143.

† Ibid. p. 151.