FERTILIZERS. 83 



which contains some alkaline substance. During the 

 Avarni sunnner months nitrates are continuously formed 

 in this way to support plants while they are grow- 

 ing most vigorously. Young plants sijuietimes suffer 

 from the want of nitrogen in the early si)ring, beiore 

 the soil becomes sufficiently warm for the fornuition of 

 nitrates. 



Phosphoric Acid (P-.Os). — Phosphoric acid, a combina- 

 tion of phospliorus and oxygen, is not found free, but 

 in combination with i)otash, soda, lime, etc. 



It is very largely a plant food, and is especially 

 necessary for the proper ripening of jjlants and the 

 formation of seeds. Its most common form is that of 

 phosphate of lime (CaOPaOs). In this form it consti- 

 tutes about one half the substance of the bones of ani- 

 mals, which are largely used in preparing this element 

 of fertilizers. 



Potash (K2O). — Potash is also an important element 

 of fertility, which does not exist in ordinary soil in suf- 

 ficient quantity to support a continuous succession of 

 crops. 



It is generally obtained and used in the form of salts 

 of potash, as carbonate of potash (K.2CO3), chloride of 

 potash (KCl), etc. Carbonate of potash is the impor- 

 tant part of wood ashes. " New " land is generally well 

 supplied with potash in the ashes resulting from the 

 burning of trees and brush. 



Artificial Fertilizers. — To sup])ly nitrogen, phosphoric 

 acid, and jjotash to the soil, as well as certain other 

 elements which are sometimes needed, substances are 

 either manufactured, or are obtained in a natural state 

 in different parts of the world. To distinguish these 

 from ordinary farm manure, which is the most conimou 



