One part, by weight, of steam, at 212° Fahr., when condensed into cold water, is found to be capable of raising 5·6 parts of the latter from the freezing to the boiling point. See Fuel, Pit-coal, Smoke, &c.
STEAR′IC ACID. HC18H35O2. Syn. Stearin (Commercial). This is obtained from stearin (see below), by saponification.
Prep. 1. Repeatedly dissolve and crystallise
commercial stearic acid in hot alcohol, until its melting point becomes constant at not less than 158° Fahr. Pure.
2. (Chevreul.) Saponify mutton suet with caustic potassa, and dissolve the newly formed soap in 6 times its weight of hot water; to the solution add 40 or 50 parts of cold water, and set the mixture aside in a temperature of about 52° Fahr.; after a time separate the pearly matter (stearate and margarate of potassa) which falls, drain and wash it on a filter, and dissolve it in 24 parts of hot alcohol of sp. gr. ·820; collect the stearate of potassa which falls as the liquid cools, recrystallise it in alcohol, and decompose it, in boiling water, with hydrochloric acid; lastly, wash the disengaged stearic acid in hot water, and dry it.
3. (Commercial.) Ordinary tallow is boiled in large wooden vessels, by means of high pressure steam, with about 16% of hydrate of lime (equiv. to 11% of pure lime), for 3 or 4 hours, or until the combination is complete, and an earthy soap is formed, when the whole is allowed to cool; the product (stearate of lime) is then transferred to another wooden vessel, and decomposed by adding to it 4 parts of oil of vitriol (diluted with water) for every 3 parts of slaked lime previously employed, the action being promoted by steam heat and brisk agitation; after repose, the liberated fat is decanted from the sediment (sulphate of lime) and water, and is then well washed with water, and by blowing steam into it; it is next allowed to cool, when it is reduced to shavings by means of a number of knives worked by machinery, and in this divided state is placed in canvas bags and submitted to the action of a powerful hydraulic press, by which a large portion of the oleic acid which it contains is expelled; the pressed cakes are then a second time exposed to the action of steam and water, again cooled, and coarsely powdered, and again submitted to the joint action of steam and pressure; they are, lastly, melted, and cast into blocks for sale.
Obs. This product is a more or less impure mixture of stearic acid and other fatty bodies, particularly the so-called margaric acid, now generally regarded as a mixture of palmitic and stearic acids. The hard, fatty acids of vegetable origin (palmitic, cocinic, myristic, &c.), now so extensively used as candle materials, are obtained from the natural oils and butters by the process known as ‘sulphuric acid saponification,’ which consists in treating the fatty bodies with 5 or 6% of concentrated sulphuric acid at a high temperature (about 350° Fahr., produced by superheated steam), and distilling the resulting mass by the aid of steam heated to about 560° Fahr. Frequently the operations of hot and cold pressing are resorted to in order to free the product from the softer fats.
By a patent process employed at Price’s candle works the natural vegetable fats are decomposed into their constituents (fatty acids
and glycerin) by the action of superheated steam alone, without previous ‘saponification’ with lime or sulphuric acid.
Another method for the preparation of commercial stearic acid is that of Messrs Moinier and Bontigny. This process is thus described in the ‘Chemical Technology’ of Messrs Ronalds and Richardson:—Two tons of tallow and 900 gall. of water are introduced into a large rectangular vat of about 270 feet capacity.