Food for 

 Plants 



1 66 



The Unit System. 



In the wholesale fertihzer trade some raw materials are 

 bought and sold on the " uriit system." The unit is i per 

 cent., or 20 pounds per ton. 



Thus, a lot of dried blood, containing 10.50 per cent, of 

 Nitrogen, equivalent to 12.75 P^'" cent, of ammonia; is said 

 to contain I2f units of ammonia, and, quoted at ^2.50 per 

 unit, a ton will cost: 12I X ^2.50 r^ ^31.87^. 



A quotation of ^1.50 per unit of available phosphoric 

 acid means ^1.50 for each 20 pounds contained in the 

 material quoted. 



Illustration. — A manufacturer offers dissolved bone black 

 guaranteed to contain 16 units of available phosphoric acid, 

 at ^0.70 per unit: 16 X ^0.70 = $1 1.20 per ton. 



Materials Used in Making Commercial or 

 Chemical Manures. 



Nitrate of Soda or Chili saltpetre occurs in 

 vast deposits in the rainless districts on the 

 West coast of South America, chiefly in 

 Peru, Chili, and Bolivia, from whence it is 

 imported to this country for use in chemical manufacture 

 and in agriculture. As imported into the United States, 

 Nitrate ot Soda usually contains from fifteen to sixteen per 



Nitrate of Soda 

 or Chili 

 Saltpetre. 



