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sideration; it depends frequently upon the co- 

 hesion of the substances and their insolubility: 

 the climate and nature of the soil also greatly 

 influence the progress of their decomposition. 

 Convinced of the importance of nitrogen in 

 manures, Payen and Boussingault undertook a 

 series of analyses for the determination of 

 the proportion of this element in the nume- 

 rous matters used as fertilizing agents. 



The results of these labours have enabled 

 them to establish the comparative rank and 

 equivalents of the manures examined. Barn- 

 yard dung, which they consider as the normal 

 manure, is taken as the standard. We will 

 insert the tables further on. 



There is a difference of opinion as to the 

 propriety of this mode of estimating the value 

 of manures; for while all acknowledge that 

 the influence of nitrogen under assimilable 

 forms is never prejudicial to plants, but is al- 

 ways useful, and even indispensable for certain 

 purposes, Liebig contends that the efficacy 

 of manures is not proportional to their amount 

 of nitrogen. In support of this opinion he 

 cites a large number of examples. He believes 

 that the effect of the ammonia presented to the 

 plants, as a source of nitrogen, by artificial 



