FIXED OILS AND WAXES 77 



pressed oil is brown and unfit to use as a food. The pressed 

 oil is allowed to stand for some time to allow impurities to 

 settle, and it is also further purified and bleached. It contains 

 about 58.5 per cent, isolinolenin (isolinolcnic acid has the 

 same empirical formula as linolenic acid, hut a different 

 structural formula), 13.5 per cent, linolein, 13.5 per cent, 

 linoleum, 4.5 per cent, olein, and 10 per cent, of solid glycer- 

 ides, stearin, palmitin, and myristin (from myristic acid, 

 saturated, C13H27COOH). 



Linseed is the principal drying oil and has been used for 

 hundreds of years in the paint and varnish industry. Its 

 usefulness lies in the fact that a thin layer of it dries or 

 oxidizes to a hard, transparent, more or less glossy skin 

 which serves as varnish when uncolored or as a paint when 

 mixed with pigments. If linseed oil is boiled first it dries 

 more quickly on exposure to the air. Also if the oil is boiled 

 with "driers" such as lead oxide, lead resinate, manganese 

 borate, and manganese resinate, the drying process is 

 hastened, probably by the metallic salts acting as catalytic 

 agents in the oxidation. Raw, or unboiled oil is used for 

 making soap, some kinds of paints and varnishes, and for 

 rubber substitutes by "vulcanizing" with sulphur or sulphur 

 monochloride. The boiled oil is used for paints, printer's 

 inks, oil-cloth, linoleum, etc. 



The oxidation process which drying oils undergo develops 

 considerable heat. Cotton waste or similar material soaked 

 in linseed oil has been known to take fire spontaneously, the 

 loose mass of material preventing the radiation of the heat 

 which gradually increases to the "flash point." 



Press cake from hot pressed linseed oil makes an excellent 

 cattle food. The cold pressed cake is more apt to poison 

 cattle due to the presence of a hydrocyanic acid glucoside 

 which is acted upon by an enzyme in the presence of water 

 with consequent hydrolysis to hydrocyanic acid and glucose. 

 The former is the poison. Hot pressed cake on the other 

 hand has had the enzvme destroved bv heat and no hydro- 

 lytic action takes place, the glucoside itself being harmless. 



(e) Olive Oil is made by pressing the fruit pulp and the 

 seeds. The cold pressed oil from the former is the better 



