J. F. Tocher 



1-27 



found a greater solubility for short periods of contact when compared 

 with long periods and established the fact that adsorption of phosphate 

 took place during long periods of contact. 



II. CITRIC SOLUBILITY— OFFICIAL AXD OTHKRWLSE. 



The writer was attracted to this subject by the fact that the citric 

 solubihty of certain commercial phosphates was determined in a dilute 

 citric acid solution ((»-"2 per cent.) and not by means of the 2 per cent, 

 solution prescribed by the official test for slags. 



Samples of ground mineral phosphate are occasionally guaranteed to 

 contain as much as 50 per cent, "citric soluble" phosphate. To the un- 

 wary this might be taken to mean that the sample contained 50 per cent, 

 "citric soluble" phosphate as determined by the official test for slags 

 and "basic superphosphates" prescribed in the Regulations. As a matter 

 of fact, however, the citric solubility in this case was determined for 

 the sellers by agricultural analysts by agitating for half an hour 5000 

 parts of a solution of citric acid (0-2 per cent, strength) with 1 part of 

 the sample. That is to say the amount of the citric acid employed was 

 one-tenth of the amount officially prescribed while the proportion of 

 fertihser was 50 times less than the proportion prescribed as may be 

 seen from the following table (Table I). 



Table I. 



Test 

 Official quantities ... 

 Quantities for private test 

 i.e. ... 



Citric 



acid 

 10 grams 



1 gram 

 10 grams 



Fertiliser 

 .5-0 grams 

 O-I gram 

 10 ,. 



Total 



volume 



.500 c.c. 



.500 „ 



5000 „ 



The following results (Table II) were obtained on using the official 

 citric solubihty test on samples of ground mineral phosphate and basic 

 slag: 



Table II. 



