78 THE CHEMISTRY OF THE FARM. 



grain in the table shows an " albuminoid ratio " of 1 : 6.6, 

 and the composition of decorticated cotton cake an 

 albuminoid ratio of 1 : 1.5. Figures so calculated are, 

 however, only approximate, as we ought clearly only to 

 take account of the constituents actually digested by the 

 animal. We shall therefore refer to the subject again 

 further on. 



Most foods supply a sufficient quantity of the ash con- 

 stituents which are required for the formation of bone 

 and tissue ; the chief of these are phosphoric acid, lime, 

 and potash. 



The oilcakes and bran are the foods richest in phos- 

 phoric acid ; straw and meadow hay are the foods poorest 

 in this constituent. Lime is most abundant in clover 

 hay, bean straw, and turnips, and occurs in least quantity 

 in the cereal grains and in potatos. Potash is abundant in 

 roots, hay, bean straw, bran, and oilcake, and is found in 

 smallest quantity in the cereal grains. 



Of all the ash constituents lime and soda are probably 

 the most generally deficient. Maize is of all ordinary 

 foods (rice excepted) the poorest in lime; it certainly 

 contains too small an amount for a rapidly growing 

 animal. At Rothamsted a mixture of coal ashes, common 

 salt, and superphosphate was used with advantage in the 

 case of pigs fed solely on maize. It must be recollected, 

 however, that animals will generally receive no incon- 

 siderable amounts of lime in their drinking water. 



The proportion of phosphoric acid and potash in various 

 foods is shown in the table on page 114. 



Digestibility of Foods. — Our knowledge concerning 

 the digestion of food by farm animals is almost entirely 



