136 PLANT PRODUCTS 



soon as the pressure is applied the oil begins to run out, and 

 is collected in a well. On long standing, small quantities 

 of mucilage are formed in the oil. For the best qualities 

 of oil the crude oil is filtered. I^inseed can be extracted 

 with petroleum spirit, but it is very rarely treated in this 

 way, because linseed cake rich in oil has a high value as 

 cattle food. 



Dark linseed oil is commonly refined by treatment with 

 sulphuric acid. The refined oil is also subjected to sun 

 bleaching in some cases. linseed oil, in addition to the 

 ordinary fatty acids, contains linoleic and linolenic acids. 

 Linseed oil has a high iodine value, and is a drying oil 

 occupying the first rank. Boiled oil is obtained by heating 

 linseed oil to a temperature of about 150 Cent., with the 

 addition of driers, which often contain manganese and lead. 

 Linseed oil is also vulcanized by sulphur chloride to form a 

 rubber substitute (see p. 165). 



The remaining linseed cake as it comes out of the press 

 is still somewhat warm, and is sometimes dipped in water, 

 to give the cakes a bloom. It is then sold for cattle food. 

 Under ordinary farm conditions, where the chief .part of the 

 home-grown food consists of hay, straw, turnips, and tail 

 corn, the purchase of a food containing some oil is highly 

 desirable, and linseed is one of the most popular of these 

 materials. linseed cakes generally contain about 1 1 per cent, 

 of oil, rather less in those of American manufacture, rather 

 more in those of Russian origin, about 32 per cent, of 

 albuminoids, rather more in cakes of American origin, and 

 rather less in cakes of Indian origin, and do not contain 

 more than about 7 per cent, of fibre. I^inseed cake is reckoned 

 as one of the safest of cattle foods, and is a favourite for 

 rearing calves on. lyinseed contains a cyano-genetic 

 glucoside called linimarin, which, by the action of the proper 

 enzyme, contained in the linseed, will develop prussic acid, 

 acetone, and glucose under certain conditions. If ground 

 linseed cake be placed in water at temperatures between 

 20 and 60 Cent., the action of the enzyme on the linimarin 

 will begin. The rate at which the prussic acid is evolved 



