SOLUBLE PHOSPHORIC ACID. 145 



of iron and alumina. As carbonate of lime and 

 fluoride of calcium are always found in bones 

 and mineral phosphates, the sulphuric acid first 

 decomposes these substances and produces sul- 

 phate of lime, before any phosphoric acid is 

 liberated or rendered soluble, because the above 

 named compounds are held together by a feebler 

 affinity than phosphoric acid with its base. 

 Hence, if an insufficient amount of acid is used 

 to effect both, the phosphoric acid is left in its 

 inert insoluble state. Through the cupidity and 

 ignorance of the "manufacturers in purchasing 

 mineral phosphates that contain a large amount 

 of these substances, this is often the case, and 

 thus they neglect their own, as well as the 

 interest of the farmer. Again, as all mineral 

 phosphates contain peroxide of iron and alumina, 

 some as much as 15 per cent., a much larger 

 amount of sulphuric acid is required to render 

 the phosphoric acid soluble than otherwise, be- 

 cause the phosphoric acid first liberated combines 

 with the peroxide of iron and alumina and be- 

 comes insoluble, and an additional amount of 

 acid is required to again liberate it from this 

 peroxide of iron and alumina. Hence, the im- 

 portance of the buyer knowing the percentage of 

 these substances in the mineral phosphate, and 

 the amount of sulphuric acid used. Here again 

 buyers are defrauded, in consequence of the 



