io THE CHEMISTRY OF CATTLE FEEDING 



plants. They appear to be in some way connected with the 

 formation of starch and are usually found in largest proportion 

 in those plants and parts of plants which contain considerable 

 quantities of that ingredient. The laws of diffusion have 

 been invoked to account for the accumulation of potassium 

 compounds in plants ; but the explanation leaves something 

 to be desired, unless it be assumed that the potash is with- 

 drawn from solution, i.e. that it is converted into insoluble 

 compounds such as potassium hydrogen tartrate. In the 

 ash of plants the potash occurs chiefly as the carbonate. 



Potassium compounds appear to be of minor importance 

 in the economy of animals. They occur in the blood of all 

 herbivora as a necessary consequence of their presence in the 

 food. The perspiration which exudes from the skin contains 

 a small amount of potash, and the suint l of sheep's wool 

 contains a more considerable quantity. The suint, which is 

 soluble in water, is removed by washing the fleece, and also, 

 more or less completely, when the animal is exposed to 

 rain. 



Potassium compounds, reckoned as K 2 O, form nearly one- 

 quarter of the total ash of milk, so that the daily yield (say 

 3 gallons) of each cow contains about one ounce of that 

 substance. A farmer producing milk therefore will find it 

 profitable to use potash manures unless his soil is naturally 

 well stocked with that ingredient. Practically the whole of 

 the potash in the food, except what is exported in the milk, is 

 returned to the land in the droppings of the animals. 



Phosphates and calcium and magnesium compounds are 

 indispensable for the growth of plants, but their functions are 

 not well understood. The phosphates are generally found chiefly 

 in the same regions as the protein compounds and are probably 



1 Physiologically, suint also is of the nature of perspiration. It is not 

 a homogeneous substance, but consists mainly of the potassium salts of 

 several fatty acids, i.e. soaps, amongst which oleic, stearic, and cerotic 

 acids predominate. Acetic, propionic, butyric and caproic acids are also 

 present together with phenol, benzoic acid, uric acid and several amides, 

 e.g. glycocine, leucine, and tyrosine in smaller quantities. As a whole, it 

 contains about 4 per cent, of potash, and is soluble in water ; the wool fat 

 is insoluble in water but soluble in ether, etc. 



