84 THE PRINCIPLES OF AGRICULTURE. 



and natural fertilizer for the farmer, they are called 

 artificial fei'tilizers. 



The materials fur them are ohtained from a variety 

 of sources, some of the more cummun of which are 

 as follows : — 



Sources of Nitrogen. — 1. Nitrate of soda, or Chili salt- 

 peter, is extensively ol)taiued in a natural state from 

 some ])arts of South America. 



2. Sulphate of anunouia is obtained for a fertilizer 

 from " gas licpior," or the water in which illuminating 

 gas has been washed. The ammonia which the liquid 

 contains is obtained by treating it with sulphuric acid, 

 with which the ammonia combines. 



3. Fish scrap, meat scrap, dried blood, and all forms 

 of animal refuse, are rich in nitrogen, and arc generally 

 used for manufacturing fertilizers. 



Sources of Phosphoric Acid. — 1. Bones are largely com- 

 posed of pli;)S})hate of lime, which is converted into an 

 a^'ailal)le form, called snperpho^phaf<\ by an ajiplication 

 of sulphuric acid. Crushed and ground l)ones are also 

 used directly as fertilizers, but yield their phosphoric 

 acid more slowlv. Bone-ash, produced by burning bones 

 until they crinnble easily, is less valuable than ground 

 bones, as the process of burning removes from the bones 

 what nitrogen they contain. 



2. Bonc-l)lack, or charred bone, is used at sugar refin- 

 eries for cleansing sugar. After it becomes useless for 

 this ])ur])ose it is treated with sulphuric acid to convert 

 its elements into a solul)lc form, and is then sold as a 

 fertilizer. 



3. Mineral deposits arc found at various points of the 

 earth containing a large percentage of phosphate of lime. 

 Their origin is supposed to have been an accumulation of 



