Chap. I.

Properties.

The properties of margaric acid are very similar to those of stearic acid. The only characteristic difference is that it melts. at 140°, while stearic acid does not melt till heated up to 158°. Margaric acid is exceedingly soluble in alcohol and ether, but like stearic acid it is insoluble in water. It reddens litmus paper, decomposes the alkaline carbonates, and forms a genus of salts to which the name of margarates has been given.

Chevreul analyzed a number of margarates. The atomic weight of margaric acid as derived from these analyses differs somewhat, as may be seen by the following table.

Composition.

The mean of all these analyses gives us 32.996. We may
therefore conclude it to be probable that the atomic weight of
this acid is 33, which is a very little lighter than stearic acid.
Margaric acid in its common state is a hydrate compound of
Margaric acid
Water

33

1.162

It is obviously a compound of one atom acid and one atom

water.

Chevreul analyzed margaric acid by means of oxide of copper and obtained for the constituents

The number of atoms which corresponds with these numbers, and suits the atomic weight of the acid, is the following:

The atomic weight of stearic and margaric acids are the same. But margaric acid contains one atom more of oxygen, one atom less of carbon, and two atoms less of hydrogen. The number of atoms in this acid amounts to 70, while those in stearic acid amount to 72. Thus the differences between their characters, though not very striking, are accompanied by a decided difference in composition.

SECTION XXVIII.—OF OLEIC ACID.

This acid was first described by Chevreul in 1813, under the History. name of graisse fluide. It may be obtained by the following process: Make a soap by uniting linseed or hemp oil with potash. Digest it in cold alcohol free from water. The oleate of potash will be dissolved, and the margarate of potash, which exists only in small quantity, will remain unacted on. Let the solution be evaporated, and let the residue be treated with the smallest quantity of absolute alcohol capable of dissolving it. Let it be separated from the small quantity of margarate of potash that remains undissolved. Let it then be mixed with water, and decomposed by boiling it with muriatic acid.

Oleic acid thus obtained has the appearance of a colourless Properties. oil. At the temperature of 66° its specific gravity is 0.898. A few degrees below 32° it congeals into a solid mass composed of needles. It has a slight odour and taste of rancidity. It may be volatilized in vacuo without alteration. It is insoluble in water. But in alcohol of the specific gravity 0·822, it dissolves in any proportion whatever. When water is mixed with the solution the acid separates. It decomposes the alkaline carbonates, strongly reddens litmus paper, and forms a class of salts, or rather soaps, to which the name of oleates has been given.

It combines in all proportions with stearic and margaric acids. When such a compound is treated with cold alcohol, much of the oleic acid is dissolved, together with a little of the stearic or margaric acid. When we treat the same compound with alcohol heated up to 140° the whole is dissolved. As the solution cools crystals of stearic acid or margaric acid are deposited, containing a little oleic acid. At a low temperature oleic acid unites with sulphuric acid without decomposition.

Chap. I.

Constituents.

atomic weight of oleic acid is only 28-48. For 3·95: 100 :: 1.125: 28.48. But little reliance can be put in this estimate, as doubtless the acid contained hygrometrical water.

Chevreul analyzed the acid by means of oxide of copper, and found its constituents to be

The number of atoms corresponding with these weights and with the atomic weight of the acid, is as follows :

History.

This would make the atomic weight of oleic acid only 32.25; which is very nearly the mean of that deduced from the analyses of oleate of barytes, and oleate of lead.*

SECTION XXIX.-OF PHOCENIC ACID.

This acid was discovered by Chevreul in 1817, and described by him in 1818, under the name of delphinic acid. He afterwards changed the name to phocenic to avoid ambiguity, as the term delphine had been already applied to a vegetable principle. This acid exists in the oil of the porpoise (delphinus globiceps). It exists also in small quantity in train oil, and in the berries of the viburnum opulus.

To prepare it a soap must be made in the usual way of porpoise oil and potash. This soap is to be decomposed by tartaric acid, and the aqueous liquid freed from the stearic, margarie, and oleic acids is to be put into a close flask with more tartaric acid. By this means most of the potash is precipitated in the state of bitartrate. The liquid being distilled, phocenic acid comes over along with the water. Saturate the acid thus obtained with barytes, and evaporate the solution in order to obtain phocenate of barytes in the state of crystals. Put 100 parts of phocenate of barytes into a narrow glass tube shut at one end. Pour upon them 205 parts of aqueous phosphoric acid of the specific gravity 1∙12, and agitate with a platinum wire. We

* Chevreul sur les corps gras, p. 75.

obtain, 1. Solid phosphate of barytes; 2. An aqueous liquid saturated with phocenic acid; and 3. Hydrated phocenic acid which swims upon the aqueous liquid. Draw off the phocenic acid by means of a sucker; and distil it by a gentle sand heat. The liquid in the receiver consists of two different layers. That next the bottom is small in quantity, and seems to be a simple solution of phocenic acid in water. The upper layer is much more abundant. It is a hydrated phocenic acid of the specific gravity 0.933, at the temperature of 82°. To obtain it quite pure, macerate it in a small retort over two or three times its weight of chloride of calcium, during four days. Then distil over a water bath till nothing more come over. The acid thus obtained has a specific gravity of 0·932 at 68°, and does not precipitate nitrate of silver.

Class I.

Div. IL

Phocenic acid thus prepared is a limpid colourless liquid like Properties. a volatile oil. It does not congeal though cooled down to 16°. It boils when heated a few degrees higher than 212°. It may be distilled over without decomposition. It has a strong smell, quite peculiar; but bearing some analogy to that of acetic acid and of rancid butter. It stains paper like oil, and gives to those bodies a disagreeable, smell like that of rancid train oil. It has a sharp acid taste, with an etherial impression.

At the temperature of 86°, 100 parts of water dissolve about 5-5 parts of this acid. Alcohol of the specific gravity 0·794 dissolves any quantity of it whatever. It dissolves in sulphuric and also in nitric acid without undergoing any alteration. It burns like a volatile oil. It combines with the different bases, and forms a genus of salts called phocenates. Chevreul analyzed several of these salts, and found the composition as follows: 1. Phocenate of barytes.

The numbers after phocenic acid in each analysis represent the atomic weight of the acid. The mean derived from the three preceding analyses is 11.44. The atomic weight derived from phocenate of lime is 10-79.

Chevreul subjected the acid itself to analysis, by heating

Chap. I.

Composition,

phocenate of lead with oxide of copper. He obtained for the constituents of the acid,

History.

The number of atoms which correspond with these constituents, and with the atomic weight of the acid, is as follows,

This number almost coincides with that deduced from the analyses of the phocenates. Perhaps we might, without impropriety, leave out the half atom of hydrogen, in which case the atomic weight would be reduced to 11:375.

The hydrated phocenic acid, according to Chevreul's analysis, is a compound of

We see from this that it is a compound of 1 atom acid and 1 atom water.*

SECTION XXX.-OF BUTYRIC ACID.

The existence of this acid was announced by Chevreul in 1814; but it was not till the year 1818 that he succeeded in obtaining it in a state of purity. It may be obtained by the following process:

Butter is to be converted into a soap precisely in the way described when treating of stearic acid. The soap is to be decomposed, and distilled exactly as was described in the last section for procuring phocenic acid. The distilled liquid is to be saturated with barytes and evaporated. The matter obtained is a mixture of butyrate, caproate, and caprate of barytes. It must be digested in 2·77 times its weight of cold water for 24 hours. The undissolved portion is to be again digested 24 hours in 2-77 times its weight of water, and this must be repeated till nothing remains undissolved but carbonate of barytes. butyrate of barytes is soluble in 277 times its weight of cold

* Chevreul, sur les corps gras, p. 99.

As