No. 6. DEPARTMENT OF AGRICULTURE. 821 



Or, taking it another way: 



TOTAL PHOSPHORIC ACID. 



The total phosphoric acid is the sum of all the forms of phosphoric 

 acid which a given fertilizer contains. In ordering dissolved rock, 

 for instance, the total is equal to the soluble, reverted and insoluble 

 phosphoric acid contained therein. 



METHOD OF MANUFACTURING SOLUBLE PHOSPHATES. 



The process of manufacturing soluble phosphates from bones or 

 mineral phosphates is not very complicated, yet requires some chem- 

 ical knowledge and experience, and facilities for carrying on the 

 operation. The raw phosphates, whether of animal or mineral 

 origin, are quite variable in their physical condition and chemical 

 composition, yet the phosphoric acid will be found to be combined 

 with lime, in the proportion of one part of the former to three of the 

 latter, forming the tri-calcium phosphate. 



The chief result which the manufacturer desires to arrive at is to 

 make the tri-calcium phosphate soluble in water or in neutral am- 

 monium citrate. To do this the chemist has worked upon the follow- 

 ing basis: Sulphuric acid is known to be more energetic in its ac- 

 tion at ordinary temperature than any other acid used in industry. 

 It, therefore, has the power of displacing all other acids from their 

 salts and of taking their bases to itself to form sulphates, which, 

 for the most part, are quite staple and easily handled substances. 

 The acids which are chiefly present in natural phosphates are phos- 

 phoric, carbonic, fluoric and silicic. These, when brought in contact 

 with dilute sulphuric acid, are all displaced, and the bases become 

 sulphates. Chemists have determined how much sulphuric acid 

 is required to displace each of the various acids present, and to 

 form sulphates with the bases with which they are combined, so 

 that, after the composition of a natural mineral phosphate has been 

 determined, the amount of sulphuric acid of a given strength which 



