INDUSTRIAL USES 33 



oxide ; such oil is known as boiled oil. A similar effect may 

 be produced by dissolving in it certain salts known as " driers," 

 such as lead linoleate or the metallic salts of resin acids, etc. 



Varnish consists of a mixture of boiled oil with gum resins 

 and oil of turpentine. 



Castor Oil is obtained by compressing the seeds of 

 Ricinus communis either with or without the application of 

 heat. The seeds contain a fat-splitting enzyme * or lipase 

 which is employed commercially for the hydrolysis of fats ; 

 they also contain a very poisonous toxalbumin, known as 

 Ricin, which remains in the residues after the expression of 

 the oil. Castor oil is a thick viscid colourless liquid ; when 

 heated above 280° it decomposes with the formation of 

 oenanthol, a substance having a very unpleasant odour. 

 Castor oil is largely used in the dye industry ; for this purpose 

 it is converted into the so-called turkey red oil, used for alizarin 

 dyeing, by treatment with sulphuric acid and neutralization 

 of the resulting sulphonic acid with soda. 



For the manufacture of hard toilet soap the following 

 fats and oils are used : tallow fat, palm oil, palm-kernel oil, 

 coco-nut oil, and olive oil ; the fats are boiled with caustic 

 soda until saponification is complete, whereupon the mixture 

 is saturated with common salt. The soap, being insoluble in 

 strong salt solution, rises to the surface leaving the glycerol and 

 salt in the aqueous layer below ; the latter is then run off and 

 the scum, which is allowed to harden in moulds, is known as 

 hard soap. Soft soaps are prepared by boiling the cheaper 

 oils, such as hemp-seed oil, cotton-seed oil or linseed oil with 

 caustic potash ; when saponification is complete the mixture 

 is allowed to set to a semi-solid without the addition of 

 sodium chloride ; the resulting mixture contains all the 

 gycerol together with the excess of alkali and a quantity of 

 water. 



Most of the gycerol of commerce is obtained from fats ; 

 it is used largely for the manufacture of dynamite. 



* The occurrence of a lipase is common to most fatty seeds, but the 

 only one commercially utilized is that of the castor bean, on account of 

 its high concentration and activity. 



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