J. F. Tocher 139 



dissolved aad «2 = weight of mineral phosphate taken for the particular 

 dilution v then 100 — = Pi= amount of phosphate dissolved as a per- 



centage of amount of mineral phosphate taken. The number of gram- 



,,...,,.. , , . 10 1000 



molecules oi citne acid per litre in each case may be written -rr-^r x = ic 



^ ■' 2]0 r 



where v is the dilution. The amount of phosphate theoretically obtainable 



expressed as tricalcium phosphate is therefore «'/3 = x gram-molecules 



per litre. The amount of phosphate found also expressed as tricalcium 



phosphate in gram-molecules per litre is 



310 



1000 



V 



y- 



Table IX. Table .showing atnount of pliosphale found per cent, of 

 amount theoreticaUij obtainable, at various dilxtionfi on basis of equation, 

 Section IV. 



Gram-molecules per litre 



Now the number of gram-molecules dissolved expressed as a per- 

 centage of the number of gram-molecules theoretically obtainable is 

 clearly 



y X 100 = p, X 



63a, 



P2- 



X ^ ' 310 



In the series under consideration a, = 5 ^^^ thus we have 



63 



Ih = Pi 



62 



10 16 7^1. 



With increasing values of a^ it is known that a smaller series of values 

 of jjj would be obtained (see Table VIII). For example, if 40 grams of 

 mineral phosphate were taken then p.^^ = Sjjj (approximately). The results 

 in Table IX merely illustrate the well-known fact that solubihty depends 

 on the hydrogen ion concentration. They further show that it is mis- 

 leading to adopt a particular set of weights to test citric solubility and 

 to express the solubility in terms of the weight of mineral phosphate taken 

 for the experiment, if it is intended to judge the equality of a phosphatic 

 fertiliser by the result so obtained. 



