46 THE CHEMISTRY OF CATTLE FEEDING 



cent, of that ingredient. The organic matter of bones also 

 includes a considerable quantity of fat. 



Beef and mutton suet, when dried and separated from skin 

 and other adventitious impurities, are popularly called tallow. 

 Hog's fat, similarly purified, is called lard ; it has a somewhat 

 lower melting point than tallow, owing to the larger propor- 

 tion of olein which it contains. 



Melted tallow and other fats gradually resolidify on 

 cooling, and a partial separation of the ingredients can be 

 effected by pouring off the more liquid portion. The final 

 products obtained by repeating this process several times, 

 differ considerably as regards their melting points, but they 

 are not even approximately pure glycerides. 



Fats do not form part of the tissues of plants as they do 

 in animals. They are chiefly stored up in the seeds as 

 nourishment for the embryo, but they occur also, in smaller 

 quantities, in the vegetative organs. 



The vegetable fats are extracted from seeds (a) by the 

 application of heat and pressure, (b) by means of solvents. 

 Oily seeds may contain from 40 to 50 per cent, of oil, and 

 from 60 to 80 per cent, of the whole is removed in the former 

 process. The compressed residues therefore contain about 

 10 per cent, of oil, and are correspondingly richer than the 

 original seeds in all other ingredients. They are called oil 

 cakes (p. 273), and are largely used for feeding cattle. 



When the oil is extracted by means of solvents, the residue 

 is obtained in the form of a meal or powder. The solvents 

 remove a larger percentage of the fat; the residual meals, 

 therefore, as a rule, contain a smaller proportion of that 

 ingredient, and, of course, a correspondingly larger proportion 

 of the others. 



The crude fats extracted from the seeds are purified by 

 processes of filtration, oxidation, reduction, washing with water, 

 acids, alkalis, exposure to heat, light, etc., as the particular 

 case may require. 



The natural fats are not simple pure glycerides, but mixtures, 

 and their composition and properties are not absolutely con- 

 stant, but only approximately so. It is, therefore, often very 



