LIQUID MANURE. 301 



verted into carbonic acid, water, ammonia, &c. The 

 time required for this change varies from four to 

 eight weeks, or even more, according to the season 

 of the year ; putrefaction being much more rapid in 

 hot than in cold weather. 



798. The substances containing nitrogen are those 

 which first begin to undergo putrefaction, and ac- 

 cordingly ammonia is one of the earliest products of 

 the putrefaction of liquid manure ; at this time much 

 of the ammonia is in the caustic state, and hence it 

 is not so fit for manure as it is subsequently, when 

 combined with carbonic acid in the completely putre- 

 fied liquid. In consequence of the great volatility 

 of caustic ammonia, much of it is lost by evaporation, 

 in the early stage of putrefaction ; it is for this rea- 

 son that close tanks for liquid manure are so much 

 recommended, and that the addition of fixers is found 

 advantageous. 



799. Amongst the principal animal substances 

 employed as manures are urine, and dung of all 

 kinds, the flesh and blood of dead animals, fat and 

 oily matters, hair, wool, skin, and, lastly, horns, 

 hoofs, and bones. These substances are all more or 

 less valuable, as yielding to the soil a large quantity 

 of the substances which constitute the food of plants; 

 they putrefy, and their elements form new combina- 

 tions with great rapidity. Those which change most 

 readily, of course yield ammonia and carbonic acid 

 most rapidly, and these constitute the most powerful 



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