On Superphosphate of Lime. 



215 



with water to form gypsuin_, and the quantity of water with which 

 V6^ parts woukl combine is 35 parts ; so that, in acting on 100 

 parts of carbonate of lime by sulphuric acid, we produce 171 parts 

 of gypsum. 



We proceed to calculate the theoretical quantity of acid to be 

 applied to 100 lbs. of bones having the composition given in the 

 analysis : — 4 lbs. of carbonate of lime will neutralize about 3^ 

 lbs. of real acid, which is furnished m round numbers by 4 lbs. of 

 oil of vitriol and by 5 lbs. of brown acid (sp. gr. 1*70). The 

 product will be 6 lbs. of gypsum. 



The acid next attacks the phosphates, w4iich may practically 

 be considered as consisting entirely of phosphate of lime. By 

 calculations previously given (page 209). the 46 parts of phosphate 

 of lime will be entirely converted into bi-phosphate by 25 lbs. of 

 oil of vitriol or by 32 lbs. of acid of density T70. 



It is to be understood that the phosphate and carbonate are the 

 only substances in bones that serve to neutralize or use up the 

 acid ; for although sulphuric acid attacks gelatine and other 

 animal matters, it does not do so to any considerable extent without 

 heatj especially when diluted. Great heat is undoubtedly produced 

 in the mixture of bones and acid, and the form.er are blackened 

 by the combined action ; but this very heat serves to accelerate 

 the solution of the bones and to employ the acid to its legitimate 

 purpose. I do not believe, therefore, that any considerable 

 amount of acid is got rid of except by the carbonate and the 

 phosphate. 



100 lbs. of raw bones then require of oil of vitriol — 



lbs. 



To neutralize the carbonate . . . . .4 

 To convert the whole phosphate into bi-phosphate . 25 



29 



So far as we are in a position to judge, therefore, from chemical 

 data^ which in such a case are paramount, we are using abund- 

 ance of acid when we employ oil of vitriol to the extent of l-3rd 

 oi the weight of the raw bones; that is to say, always supposing 

 that the bones are finely crushed, the acid suihciently diluied, and 

 the mixture well made. 



I think the recommendation that has been made, and very 

 commonly acted upon, of treating the bones one -half \heir 

 weight of oil of vitriol, is so far unfortunate that farmers have 

 been thereby put to an unnecessary expense, for, as will pre- 

 sently appear, the acid is by far the most costly material in the 

 manufacture. One-third of acid seems cjuite enough, especialh^ 

 when the farmer makes the superphosphate for his own use, 

 because it is not important to him to decompose the whole of 



