AGE AND KIND OF STOCK 145 



duct of respiration, and forms ammonium carbonate, 

 a volatile compound. When the stable atmosphere 

 becomes charged with ammonium carbonate some of 

 it is deposited on the walls of the stable, forming a 

 white coating. The white coating found on harnesses 

 and carriages stored in poorly ventilated stables, is 

 ammonium carbonate. Accumulations of manure in 

 the stable and poor ventilation are the conditions fav- 

 orable to the production of this compound. 



182. Human Excrements. The use of human ex- 

 crements as manure is sometimes advised, and in some 

 countries they are extensively used. When fresh, 

 they may contain a high per cent, of nitrogen and 

 phosphoric acid ; when fermented, a loss of nitrogen 

 has occurred. Heiden estimates that in a year 1,000 

 pounds of excrements per person are made, which 

 contain #2.25 worth of fertility. 59 For sanitary rea- 

 sons, human excrements should be used with great care. 

 It is doubtful with the abundance and cheapness of 

 plant food whether their extensive use as manure is 

 advisable. About 1840, Leibig expressed the fear that 

 the essential elements of plant food would accumulate 

 in the vicinity of large cities and be wasted, and that 

 in time there would be a decline in fertility due to 

 this cause. 60 Many political economists shared the 

 same fear. Since that time the fixation of atmos- 

 pheric nitrogen through the agency of leguminous 

 crops has been discovered, extensive beds of sodium 

 nitrate, phosphate rock and Stasfurt salts, have been 

 utilized and larger areas of more fertile soils have been 



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