Chemical Content of Manure 305 



Chemical composition and bacteria' change. — The 

 chemical composition, like the mechanical constitution 

 of manure, exerts a direct influence on the rapidity 

 and extent of the bacterial changes. It is to be remem- 

 bered that the sohd excreta represent the undigested 

 portion of the food. They are largely insoluble in water 

 and not readily attacked by most of the manure bac- 

 teria. The materials used as litter, such as straw, saw- 

 dust, leaves, and peat, are, likewise, somewhat resistant 

 to the attacks of the microorganisms. On the other hand, 

 the liquid excreta represent the food materials that 

 have been broken down into simpler substances in the 

 process of digestion and have passed through the kidneys 

 in a soluble state. On account of their comparatively 

 simple composition and their solubility, these substances 

 are readily accessible to bacterial changes. Their pro- 

 portion in the manure intimately affects the rate of 

 the decomposition of the latter. 



The following table, also given by Beal, shows the 

 composition of the solid and liquid excreta of different 

 farm animals: 



Water Nitrogen Phosphoric acid Potash and soda 



Per cent Per cent Per cent Per cent 



Solid Liquid Solid Liquid Solid Liquid Solid Liquid 



Horses 76 89 .50 1.20 .35 Trace .30 1.5 



Cows 84 92 .30 .80 .25 Trace .10 1.4 



Swine 80 97.5 .60 .30 .45 .125 .50 .2 



Sheep 58 86.5 .75 1.40 .60 .050 .30 2.0 



The most noteworthy facts brought out by the table 

 are the comparatively large proportion of nitrogen and 

 of potash in the liquid excreta and the presence of almost 

 all of the phosphoric acid in the solid excreta. Notwith- 

 standing the great dilution of the liquid excreta, they 



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