No. 1. DEPARTMENT OE AGRICULTURE. 138 



PHOSPHORUS. 



The element, phosphorus, does not occur in the free state, but is 

 found associated with other elements in the form of phosphates. 

 Phosphoric acid is made up of the elements, phosphorus, oxygen and 

 hydrogen. Free phosphoric acid does not occur in nature, but when 

 the hydrogen of this acid is replaced by a base, as for instance, with 

 lime, iron or alumina, we have a lime, iron or alumina phosphate. 

 The raw materials, which furnish phosphorus for commercial fer- 

 tilizers, contain it usually in the form of phosphate of lime or tri- 

 calcium phosphate. In this condition the phosphate is insoluble in 

 water and in the slightly acid soil water. That is to say^ they are 

 not in a condition in which they will be of immediate use to grow- 

 ing crops. 



Liebig, reference to whom has already been made, was the first 

 to suggest the treatment of calcium phosphates with sulphuric acid 

 in order to render the latter easily soluble in water. This was about 

 1840, and the manufacture of artificial fertilizers dates from about 

 this time. The phosphoric acid is present in bones in South Caro- 

 lina, Florida and Tennessee rock in the same form, that is, as tri-cal- 

 cium phosphate, 168 parts lime being united with 144 parts of phos- 

 phoric acid to form 310 parts of phosphate of lime, or as manufactur- 

 ers sometimes speak of it, bone phosphate of lime. Now, when these 

 insoluble phosphates are treated with sulphuric acid, a change is 

 brought about in the relation of these elements to each other. The 

 sulphuric acid unites with a part of the lime to form sulphate of lime 

 or gypsum. The remainder of the lime and phosphoric acid unites 

 w ith water to form one lime calcium phosphate. This reaction may 

 be represented by the following formula: Ca^ (Po*)^ + 2W- So*= 

 2Cas o* + Ca H^ (Po^)^ 



312 parts tri-calcium phosphate + 196 parts sulphuric acid=272 

 parts gypsum + 236 parts mono-calcium phosphate. 



This mono-calcium phosphate, or one lime phosphate, is the so- 

 called soluble phosphoric acid of the trade. 



Perfect reaction, however, seldom occurs. Less sulphuric acid is 

 used than would be required to convert all the phosphoric acid into 

 soluble phosphate. Reaction takes place in part as above and in 

 part as follows: 



Ca= (Po^y + H" So^=Cas o* + Ca^ H^ (Po*)' 

 312 parts + 98 parts=136 parts + 274 parts. 



This last product is di-calcium phosphate or the so-called reverted 

 phosphate acid. In addition to this, a small part of the original 

 lime phosphate usually remains unacted upon, forming the insolu- 

 ble phosphoric of the manufactured product. The manufacture of 



