844 SOAP 



Oils and fats consist chiefly of oleine and stearine, as in tallow, suet, and several 

 vegetable fats ; of margarine, which occurs in animal fats, in butter, in olive and other 

 vegetable oils ; of palmitine, which is found in palm oil ; and so on with various other 

 immediate principles, according to the nature of the fats and oils employed by the soap- 

 maker. Natural fatty substances, however, are never exclusively formed of one of 

 these principles, but are, on the contrary, composed of several of them in various pro- 

 portions, oleine alone being a constant constituent in all of them. 



Natural or neutral fats and oils, chemically considered, are really salts, sometimes 

 called ' glycerides ; ' that is to say, are combinations of acids, oleic, stearic, margaric, 

 acid, &c., with the oxide of a hypothetical radical called glyceryl. 



Stearine being, therefore, a combination of stearic acid with oxide of glyceryl, is a 

 stearate of oxide of glyceryl. 



Oleine is a combination of oleic acid with oxide of glyceryl, and is, therefore, an 

 oleate of oxide of glyceryl. 



Margarine is a combination of margaric acid and oxide of glyceryl, and is, there- 

 fore, a margarate of oxide of glyceryl, and so on with the other constituents of fats 

 and oils. 



Glycerine is a combination of oxide of glyceryl with water, which, in that case, 

 plays the part of an acid to form a hydrate of oxide of glyceryl (glycerine). 



Now, when neutral fats (namely, oleine, stearine, margarine, &c., or the fats or oils 

 which they constitute) are treated by solutions of caustic alkalis, such as potash or 

 soda, their constituents react* upon each other, and combine with the potash -or soda ; 

 and provided too great an excess of alkali has not been used 1 , the fat or oil dissolves in 

 the alkaline sohition into a syrupy liquid, which on cooling forms a gelatinous mass 

 which is nothing else than an aqueous solution of soap mixed with the glycerine, 

 which the treatment has set free. 



The following equation, in which, for the sake of simplicity, one of these principles 

 only, stearine, and soda dissolved in water, are taken as examples, will clearly illustrate 

 this interesting reaction : 



Stearine. 



Stearate of oxide of glyceryl 4- soda + water 

 = stearate of soda + hydrate of oxide of glyceryl 



hard soap. glycerine. 



In the same way : 



Oleine. 



Oleate of oxide of glyceryl + soda + water 

 = oleate of soda + hydrate of oxide of glyceryl 



hard soap. glycerine. 



According to the modern views of chemists, however, glycerine may be regarded as 

 propenylic alcohol, one of the group of triatomic alcohols. The natural fats then 

 become triatomic ethers of the fatty acids ; thus stearine (tristearine) consists of pro- 

 penyl tristearate. All soaps are metallic salts of the fatty acids, or mixtures of 

 those salts. 



Soaps made with soda are hard ; those made with potash are soft ; the degree of 

 hardness being so much greater as the melting-point of the fats employed in their 

 manufacture is higher, hence the more oleine a fatty matter contains, the softer the 

 soap made with it will be, and vice versa. The softest soap, therefore, would be that 

 made altogether with oleine (oleic acid) and potash (oleate of potash) ; the hardest 

 would be that made with stearine and soda (stearate of soda). 



The fats or oils employed for the manufacture of soaps, are tallow, suet, palm oil, 

 cocoa-nut oil, kitchen fat, bone-grease, horse oil or fat, lard, butter, train oil, seal oil, 

 and other fish oils, rape oil, poppy oil, linseed and hempseed oil, olive oil, oil of 

 almonds, sesame, and ground-nut oil, and resin. This last substance, though 

 very soluble in alkaline menstrua, is not, however, susceptible, like fats, of being 

 transformed into an acid, and will not, of course, saponify or form a proper soap by 

 itself. The more caustic the alkali the less consistency has the resi nous compound which 

 is made with it. The employment of caustic alkalis, however, is not necessary with it, 

 since it dissolves readily in aqueous solutions of carbonated alkalis, but even with 

 carbonate of soda it forms only a viscid mass, owing to its great affinity for water, so 

 that even after having been artificially dried in an oven, and thus rendered to a great 

 extent hard, the mass deliquesces again spontaneously by exposure, and returns to 

 the soft state. The drying oils, such as those of linseed and poppy, produce the 

 softest soaps. 



