STEARIC ACID, improperly called STEARINE, is the solid constituent of fatty substances, as of tallow and olive oil, converted into a crystalline mass by sa ponification with alkaline matter, and ab straction of the alkali by an acid. By this process, fats are convertible into three acids, called Stearic, Margaric, and Oleic ; the first two being solid, and the last liquid. The stearine, of which the adamantine and factitious wax candles are made, consists of the stearic and margarie acids combined. These can be separated from each other only by the agency of alcohol, which holds the mar garic acid in solution after it has depo sited the stearic in crystals. Pure stearic acid is prepared, according to its dis coverer, Chevreul, in the following way : —Make a soap, by boiling a solution of potash and mutton-suet in the proper equivalent proportions (see SOAP) ; dis solve one part of that soap in 6 parts of hot water, then add to the solution 40 or 50 parts of cold water, and set the whole into a place whose temperature is about 52° Fahrenheit. A substance falls to the bottom, possessed of pearly lustre, con sisting of the bi-stearate and bi-marga rate of potash ; which is to be drained and washed upon a filter. The filtered liquor is to be evaporated, and mixed with the small quantity of acid necessary to saturate the alkali left free by the pre cipitation of the above bi-salts. On ad ding water to it afterwards, the liquor affords a fresh quantity of bi-stearate and bi-margarate. By repeating this operation with precaution, we finally ar rive at a point when the solution con tains no more of these solid acids, but only the oleic. The precipitated bi-salts are to be washed and dissolved in hot al cohol, of specific gravity 0.820, of which they require about 24 times their weight. During the cooling of the solution, the bi-stearate falls down, while the greater part of the bi-margarate, and the re mainder of the oleate, remain dissolved. By once more dissolving in alcohol, and crystallizing, the bi-stearate will be ob tained alone ; as may be proved by de composing a little of it in water at a boiling heat, with muriatic acid, letting it cool, washing the stearic acid obtained, and exposing it to heat, when, if pure, it will not fuse in water under the 158th degree of Fahrenheit's scale. If it melts
at a lower heat, it contains more or less margaric acid. The purified bi-stearate being decomposed by boiling in water along with any acid, as the muriatic, the disengaged stearic acid is to be washed by melting in water, then cooled and dried.
Stearic acid, prepared by the above process, contains combined water, from which it cannot be freed. It is insipid and inodorous. After being melted by heat, it solidifies at the temperature of 158° Fahrenheit, and affects the form of white brilliant needles grouped together. It is insoluble in water, but dissolves in all proportions in boiling anhydrous al cohol, and on cooling to crystallizes therefrom in pearly plates ; but if the concentrated solution be quickly cooled to 112°, it forms a crystalline mass. A dilute solution affords the acid crystal lized in large white brilliant scales. It dissolves in its own weight of boiling ether of 0.727, and crystallizes on in beautiful scales of changing colors. It distils over in vacuo without alteration ; but if the retort contains a little atmos pheric air, a small portion of the acid is decomposed during the distillation ; while the greater part passes over unchanged, but slightly tinged brown, and mixed with traces of empyreumatic oil. When heated in the open air, and kindled, stearic acid burns like wax. It contains 3.4 t)er cent of water, from which it may be freed by combining it with oxide of lead. When this anhydrous acid is sub jected to ultimate analysis, it is found to consist of-80 of carbon, 12.5 hydrogen, and 7.5 oxygen, in 100 parts. Stearic acid displaces, at a boiling heat in water, carbonic acid from its combinations with the bases • but in operating upon an al kaline carbonate, a portion of the stearic acid is dissolved in the liquor before the carbonic acid is expelled. This decom position is founded upon the principle, that the stearic acid transforms the salt into a bicarbonate, which is decomposed by the ebullition.