68 PRACTICAL FARM CHEMISTRY. 



the value of fertilizing materials from different 

 standpoints. The dealer fixes the price, indepen- 

 dent of the agricultural value of the article, with a 

 view of making sales at a fair profit. The laws of 

 supply and demand rule the market, and conse- 

 quently the prices of the various substances of plant 

 food not only fluctuate quite considerably, but there 

 is also a wide difference between the prices of the 

 same element as coming from different sources. 



On the other hand, the stations — and with them 

 the farmers — look only at the real fertilizing value 

 of each substance, independent of the source from 

 which it was obtained, or the price asked for it by 

 the dealer. If a pound of nitrogen in sulphate of 

 ammonia is worth eighteen and one-half cents, a 

 pound in any other form, which would give us the 

 same results, as it did in the other form, should be 

 given the same valuation, even if the dealer asks a 

 cent or two less for it. So it is with phosphoric acid. 

 If soluble or reverted on one side, or insoluble on 

 the other, it will give us the same practical results, 

 pound for pound respectively, whether it is in the 

 form of bone black, or of South Carolina rock; 

 hence the agricultural value must be the same in 

 either case, no matter how the price of the different 

 forms may vary in the open market. 



The stations' schedule give us a fair measure of 

 comparative values, in an agricultural or practical 

 sense. A comparison of market prices of fertilizing 

 materials with the values as adopted by the stations 

 will give us a clue to the solution of the problem, 

 in what shape we may purchase our fertilizers most 

 economically. 



It hardly needs to be said that the latest schedule 

 of values should in all cases be made to serve as a 



