112 CHEMISTRY OF FARM PRACTICE 



ing drives off the combined water and makes the material 

 less soluble. 



83. Acid Phosphate or Superphosphate. This is the 

 form of phosphorus most used as a fertilizer. The reaction 

 given on page 23 by which the insoluble phosphate rock 

 is made soluble was discovered by Baron Liebig and was 

 applied by him to the treatment of bones. About 1845, 

 Lawes made use of this reaction for the treatment of the 

 newly discovered mineral source of phosphorus, coprolite, 

 and from this beginning the manufacture of phosphates 

 has grown into an immense industry. Superphosphate 

 should not be mixed with rock phosphate, lime, Thomas 

 phosphate, cyanamid, or basic calcium nitrate, because the 

 calcium contained in these materials would " revert " the 

 acid salts of calcium phosphate into the insoluble dical- 

 cium phosphate, in this way neutralizing the advantages 

 of the acid treatment. A soluble phosphate, when applied to 

 the soil, goes into solution in the soil water and is diffused 

 throughout the soil. When it comes in contact with a 

 basic material, it is precipitated in fine solid condition 

 on the surface of the soil particles. In this way, the added 

 phosphate is widely distributed, and the exudation from 

 root hairs of the plant, coming in contact with it, dissolves 

 the phosphate, which then by osmosis is taken into the 

 plant structure. 



Acid phosphate applied together with fertilizer contain- 

 ing nitrogen and potash gives the best results, the proper 

 proportions for each case varying with the soil and the 

 crop to be grown. In many cases, superphosphate, when 

 applied alone, is advantageous, especially on land well 

 supplied with organic matter. The fact that superphos- 

 phate carries with it much sulphate of lime or land plaster 

 should always be remembered in connection with the use 

 of this phosphate as a fertilizer. Land plaster has the 

 property of aiding in the breaking down of organic matter 

 in the soil and of liberating potash and phosphorus from 



