274 THE CHEMISTRY OF CATTLE FEEDING 



applied by means of a hydraulic ram or other device ; the oil 

 flows out and is collected in tanks constructed to receive it. 

 When the pressure is relaxed, after abo'ut ten minutes, the 

 residual cake is removed. It has the shape of the bag and 

 bears on its surface the impression of the mould generally 

 the name or trade mark of the manufacturer in which it was 

 made. As it comes from the press it is still hot and steamy, 

 and must be placed in a rack for a few days to dry and harden. 

 If not properly dried the cakes are liable to mildew and 

 become unfit for use as food. 



Linseed Cake. Flax is rarely grown for seed in this 

 country., The bulk of the seed comes from Russia and India. 

 Russian linseed cake commands the highest price. It is 

 generally purer and richer in composition. Bombay linseed 

 cake is rather lighter in colour, and not infrequently contains 

 foreign seeds chiefly rape and occasionally mustard. The 

 latter has a certain irritant effect on the alimentary canal, but 

 it is probably not so dangerous as it was at one time thought 

 to be. Its presence is, however, undesirable, and it is easily 

 separated from linseed by screening. 



All genuine linseed cakes, when properly made, have a 

 reddish grey colour. A dark appearance is regarded as an 

 indication of overheating. Adulteration with starchy cereals 

 gives them a lighter colour. This can easily be confirmed by 

 the iodine test (p. 25). Genuine linseed contains neither 

 starch nor sugar in perceptible quantity ; the soluble carbo- 

 hydrate is almost entirely mucilaginous in character. A small 

 quantity of the ground cake when boiled with water should 

 form a jelly on cooling. The presence of sugar can be 

 detected by Fehling's test (p. 19). Foreign seeds, husks, 

 straw, etc., if present, may be seen under the micro- 

 scope. 



For many years linseed cake has been regarded by farmers 

 as one of the safest and most satisfactory foods on the market. 

 The recent discovery of the presence in the seeds of a nitro- 

 genous glucoside which, on hydrolysis, yields pruSsic acid, has 

 naturally caused some misgivings in regard to it. Since then 

 several cases of poisoning have been ascribed to linseed cake, 



