OF ARTIFICIAL MANURES. 161 



the pecuniary value of the manure. To do this, he 

 must first ascertain what each separate chemical 

 constituent is worth ; this being known, it is simply- 

 necessary to calculate by the rule of three the cor- 

 responding value for each separate constituent, and 

 add together the separate sums. As chemical anal- 

 yses are always estimated for 100 parts, the sum 

 total gives the price for the hundred-weight of ma- 

 nure, this being assumed at 100 pounds. 



The chief difficulty consists in finding a trustwor- 

 thy and accurate criterion, by which the price of the 

 individual chemical substances that form the con- 

 stituents of manures may be determined. Many of 

 these substances (for example, nitrogen) are not met 

 with as articles of commerce, and have accordingly 

 no definite marketable value. Other substances (for 

 example, potash, soda, sulphuric acid, etc.) occur, in- 

 deed, in commerce, but only in the more or less puri- 

 fied state in which they are used for other operative 

 or domestic purposes. The commercial value they 

 possess, when so refined, cannot of course be as- 

 sumed as a basis for our calculations, inasmuch as 

 it would be greatly too high. Finally, most sub- 

 stances recognized as manuring agents, even when 

 they form an article of trade, are commonly united 

 with each other ; whence a distribution of the money 

 value between two, three, or more elements, for 

 which no sure foundation is possessed, becomes ab- 

 solutely necessary. 



In this want of certain principles, I have sought to 

 14* 



