98 ELEMENTARY AGRICULTURAL CHEMISTRY 



For many reasons, however, the proportions are liable to 

 very considerable variation. The excreta of sheep are less 

 watery than those of the other animals. 



It will be noticed that in most cases the urine, though 

 almost free from phosphates, is richer in nitrogen and potash 

 than the dung. The substances found in the urine are those 

 which have been digested by the animal and produced by the 

 waste of tissue while those in the dung are chiefly derived 

 from the undigested food. In addition to the fertilising con- 

 stituents of the urine and dung, a notable quantity of nitrogen 

 and, particularly, of potash is contained in the perspiration 

 of some animals. Horses and sheep are remarkable in this 

 respect. 



Th^ litter renders the manure more bulky and porous, 

 absorbs and retains much of the liquid portion, increases the 

 carbonaceous matter which will eventually pass into humus 

 in the soil, and furnishes a small proportion of plant food. 

 It greatly influences the fermentation of the manure, both by 

 aflfecting the porosity and admission of air and also by furnish- 

 ing certain micro-organisms. The average proportions of the 

 chief manurial ingredients present in the various substances 

 used as litter are given in the following table : — 



The absorptive and retentive power of these substances for 

 water and ammonia are of much importance. Peat-moss 



