HISTORY OF THE AMERICAN MENHADEN. 495 



7. Methods of calculating costs of valuable ingredients of fertilisers.* 



Tbo inetbod referred to on pajje 235 consists in comparing different 

 fertilizers by tbe costs per pound of tlie valuable ingredients at tbe prices 

 at wbicb tbe articles are sold. 



Tbe way in wbicb tbese com[»utations are made bere may be explained 

 as follows : 



Take first a simple case, a sulpbate of ammonia containing 20 per cent, 

 of nitrogen, and sold at $100 per ton. Twenty per cent, is equivalent 

 to 400 pounds in a ton of 2,000 pounds. Tbese 400 pounds of nitrogen 

 cost $100. One pound will tberefore cost $100 -^ 400 = 25 cents. 



Now, a more complicated case. Suppose a superpbospbate to contain 

 valuable ingredients (and tbat, for convenience, wo indicate tbe latter 

 by abbreviations), as below : 



Soluble pbospboric acid, (Sol.) 10 per cent. =200 pounds in ton, 



Insoluble pbospboric acid (Ins.) 2.5 per cent. = 50 " " " 



Nitrogen (N.) 3 per cent. = GO " <' " 



tbat it be sold at $40 per ton, and that tbe values of tbe ingredients are 

 in tbe ratios of Sol. 15, Ins. 6, and N. 25 cents per pound. Tbe problem 

 will be to find a series of values in tbe ratios 15 : 6 : 25, wbicb, multiplied 

 by the respective numbers of pounds of Sol., Ins., and N. in a ton, will 

 give three products, whose sum will be $40. Tbe method employed here 

 for solving the problem is as follows : The assumed rate for Ins. was C 

 cents, tbat for Sol., 15 cents, or 2^ times as much, and that for N. 25 

 cents, or 4i times as much. Multiply tbe number of pounds of Sol. in 

 a ton by 2^, and that of N. by 4i, and add the products to the number 

 of pounds of Ins., and the sum will be the number of pounds of Ins. 

 which would have the same value as the Sol., Ins., and N. actually present 

 taken together. Divide the whole cost by this sum and the quotient 

 will be tbe cost of one pound of Ins. This multiplied by 2J will give 

 the cost of one pound of Sol., and by 4^ will give tbe cost of one pound 

 of N. The calculations for the above case will be : 



Sol 200 pounds x 2J=500 pounds Ins. 



Ins 50 '• X 1 = 50 " " 



N 60 '' X 4i=250 " " 



800 " " 



The price per ton, $40, divided by 800, gives 5 cents, the cost of one 

 pound of Ins.; 5 x 2^ = 12^ cents cost, of one pound of Sol. ; and 5 X 

 4i= 20f, cost of one pound of N. 



*From report of Counecticut Agricultural Experimeut Station, 1876, W. O. Atwater, 

 director. 



