LINSEED CAKE. 279 



and in some cases as nitrates. Large numbers of analyses in 

 which the distinction between the nitrogen existing as albu- 

 minoids and in other forms has been made are now available* 



The composition of the more important crops of the farm 

 has been given on pages 251, 252, and 253. . 



In addition, certain concentrated foods are employed. Many 

 of these are residues from the manufacture of oil from seeds, f 

 known as oil-cakes, or of flour, &c., from grain. They consist 

 chiefly of the husk and solid portion of the seeds and are 

 usually rich in albuminoids, minerals, and oil. The chief 

 varieties of oil-cake used as food are 



Linseed cake. The composition of linseed has already 

 been given. In the manufacture of linseed oil the crushed 

 peed is treated by one of two processes (1) simple pressure 

 aided by heat, or (2) extraction by means of petroleum 

 naphtha. In the latter process, which is largely replacing the 

 older one, especially in America, the solvent is removed by 

 means of steam, and the pressed residue is then ground and 

 sent into the market as oil meal or linseed meal. The new 

 process meal is richer in protein and carbohydrates, but much 

 poorer in fat. It is also less digestible than the old process 

 meal. 



Properly ripened linseed is free from starch, though the 

 immature seed contains a small quantity. Many weed seeds, 

 perhaps accidentally mixed with the linseed, usually are rich 

 in starch. As a rule the oil extractor is careful to exclude all 

 foreign matters from the seed because of its retaining the oil, 

 which is very valuable (particularly at present, its price being 

 now [1901] about double its usual one). The presence of 

 starch, therefore, in linseed cake or meal generally indicates 

 adulteration after the extraction of the oil. 



Occasionally the husks of the castor-oil seed occur in linseed 

 cakes (probably through accident), and such cakes are often 

 poisonous. A method for the detection of such admixture is 

 described by Leather. J 



As a rule, Eussian and English cakes are richest in oil, 

 while the American products excel in nitrogenous compounds. 

 Indian cakes are poorest in albuminoids, and American ones, 



* v. Chap. XI. t r. Chap. IX., p. 205. J Jour. Roy. A grit-. Soc. 1892. 



