890 STEARIC ACID 



which must be supplied by the boiler to the engine for each horse-power, and this will 

 be the same whatever may be the magnitude or proportions of the cylinder. 



STEAM BOILERS. Did space allow of our entering on a consideration of this 

 important subject, which it does not, it would not properly fall within the scope of 

 this Dictionary : we therefore refer to the Dictionary of Engineering, and to Mr. W. 

 Fairbairn's papers in the ' Transactions of the Eoyal Society.' 



STEAm-EircINE. Steam-engines are divided into condensing and non-con- 

 densing, corresponding with those which are worked by steam at high-pressure and at 

 low-pressure respectively. The form of the 'engine is varied according as it is a 

 stationary, a locoviotive, or a' marine engine. ' For descriptions of the various forms, 

 the reader must be referred to special treatises upon the subject, such as Kankine 

 ' On the Steam-Engine.' 



STEARIC ACID. (Tdlgsiiure, Ger.) Chevreul's discovery of the constitution 

 of fats, led to the present processes for the manufacture of stearic acid. The original 

 experiments were published in 1823, and Gay-Lussac, with Chevreul in 1825, took 

 patents for the manufacture of fatty acids. Pure stearic acid is prepared, according 

 to its discoverer, Chevreul, in the following way : Make a soap by boiling a solution 

 of potash and mutton-suet in the proper equivalent proportions ; dissolve 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 in a place whose temperature is about 52 Fahr. A substance 

 falls to the bottom, possessed of pearly lustre, consisting of the bi-stearate and 

 bi-margarate of potash; which is to be drained and washed upon a filter. The 

 filtered liquor is to be evaporated, and mixed with a small quantity of acid necessary 

 to saturate the alkali left free by the precipitation of the above bi-salts. On adding 

 water to it afterwards, the liquor affords a fresh quantity of bi-stearate and bi-mar- 

 garate. By repeating this operation with precaution, we finally arrive at a point 

 when the solution contains no more of these solid acids, but only the oleic. The pre- 

 cipitated bi-salts are to be washed and dissolved in hot alcohol, 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 

 remainder of the oleate, remain dissolved. By repeatedly dissolving in alcohol, and 

 crystallising, the bi-stearate will be obtained alone, as may be proved by decomposing 

 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 Btearic 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 soli- 

 difies at the temperature of 158 Fahr., and affects the form of white brilliant needles 

 grouped together. It is insoluble in water, but dissolves in all proportions in boiling 

 anhydrous alcohol, and on cooling to 122, crystallises therefrom in pearly plates ; but 

 if the concentrated solution be quickly cooled to 112, it forms a crystalline mass. A 

 dilute solution affords the crystallised acid in large white brilliant scales. It dissolves 

 in its own weight of boiling ether of 0'727, and crystallises on cooling in beautiful 

 scales, of changing colours. Its distils over in vacua without alteration ; but if the 

 retort contains a little atmospheric 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. By analysis it is found to contain in 

 100 parts, carbon 75'6, hydrogen 12'6, and oxygen 11 -8. which agrees with the formula 

 C"H S8 < (C^H 86 1 )' Stearic acid displaces, at a boiling heat in water, carbonic acid 

 from its combinations with the bases ; but in operating upon an alkaline carbonate, 

 a portion of the stearic acid is dissolved in the liquor before the carbonic acid is 

 expelled. The decomposition is founded upon the principle, that the stearic acid 

 transforms the salt into a bicarbonate, which is decomposed by the ebullition. 



Of late years lime has been had recourse to, with perfect success, and has become 

 subservient to a great improvement in candle-making". Lime was first successfully 

 used by De Milley in 1831. The stearine block now made by many London houses, 

 though containing not more than 2 or 3 per cent, of wax, is hardly to be distinguished 

 from the purified produce of the bee. The first process is to boil the fat with quick- 

 lime and water in a large tub by means of perforated steam-pipes distributed over its 

 bottom. About 11 parts of dry lime are fully equivalent to 100 of stearine and oleine 

 mixed ; but as the lime is in the state of hydrate, 1 4 parts of it will be required when 

 it is perfectly pure ; in the ordinary state, however, as made from average good lime- 

 stone, 16 pirts may be allowed. After a vigorous ebullition of 3 or 4 hours, the 



