V,]i) The C'dric Sohihiliti/ of Mineral J'/iosp/Ki/cs 



show that if the acidity is expressed as the molecular conceutruliuu ol 

 citric acid at the end of 30 minutes shaking, K — u^jifi fairly accurately 

 describes the solubility of the phosphates at the acid concentrations 

 named. 



Table VII. Amount of miner nl phosphate present and voluine constant — 



aci(Jit>i varies. 



m^j)iu = 100; vol. =.'500 c.c. =m^: m., -miiu'ial iiliuspliiite ^5 grums 



oo 60 



lo:=°- 



gco 30 



II 20 

 If '0 



.^' 



^' 



If '0/' 



oja Wiijjht of Citric Acid in .">( 

 1 2 3 4 5 6 7 8 

 rt:»»......» -: vj„.v «,,l «., w ..., 



."iOOc.c. 



"4 5 6 7 8 9 10 



;rain 5. See columns H and 0, 

 n 



15 



Sfl 



§fe=. 

 "Sob 





W(i"lil of ('ilric Acid in .')(X)c.c. 



2345678 9 10 

 Diagram (>. See column 7, Tal>le VII. 



Oiagi 



Table VI] . 



The acconipanyini; diagrams (Diagrams 5 and (i) sliow the results of 

 Table VII. These results show clearly increasing citric solubility with 

 increasing acid concentration but with constant weight of mineral phos- 

 phate in a constant volume. In a citric solubility test, used as a measure 

 of availability, it seems necessary therefore to show that a two per cent, 

 solution is the concentration of citric acid best suited for the utilisation 

 of phosphate by the plant. Would it not be more in accordance with 

 scientific practice firstly, to a.scertain the constitution of the ])liosphatic 

 fertilisers, and secondly, to dptermine wliat rolo concentration has in the 

 life history of the plant? 



