628 



STATE BOARD OF AGRICULTURE. 



TABLE VIII. 



The results of these experiments present several interesting points. 

 In the first place there was a consistent shift of reaction in the acid 

 and neutral solutions toward the alkaline side as opposed to a lack of 

 change in these solutions when used for the analysis of fertilizers. 

 Tn this case there exists a condition just the reverse of that in the 

 previous experiments in which the reactions of the neutral and acid 

 solutions remain constant while that of the alkaline ones shifted towards 

 the acid side. 



The significance of this in the consideralion of the analysis and 

 composition of superphosphates is considerable. The simplest concep- 

 tion of superp]n>s]>hafo formation and reversion is that the natural 

 tricalcium phospliate of tlie rock is converted into monocalcium plios- 

 phate by the action of -the sulphuric acid. It then "reverts" to the 

 dicalciuin and tricalcium forms. A commercial sample of such material 

 would then contain varying quantities of (1) the orginal natural phos- 

 phate, (2) monocalcium phosphate, (3) dicalcium phosphate, (4) "pre- 

 cipitated" tricalcium phosphate, (5) calcium sulphate and (G) sulphuric 

 acid. In a consideration of the action of citrate solution (G) and 

 l)robably (2) may be omitted, however, as both are removed in the 

 washing to remove the water soluble phosphoric acid. It cannot be 

 claimed therefore that the results with the commercial products were 

 due to the sul])hui'ic acid, and the conclusion seems inevitable that 

 superphosphate formntiou and levcrsion is not the simple process out- 

 lined above. Such a ccuiclusion of course invalidates any comparison 

 between results obtained on synthetic mixtures of pure phosphates and 

 Hiose with commercial supor]»hosphatos so far as their serving as an 

 index of the composition of the latter is concerned. 



Passing to the analytical data on these pure phosjjhates, it is evident 

 that the logical conclusions of the consideration of i)revious work are 

 substantiated. The results Avith samples A., B. and C show: 



1. That the official ])rocedure classes SO-OO^^of pure dicalcium phos- 

 phate as available. 



