DETERMINAITON OF THE FREE ACID IN SUPERPHOSPHATES. 



69 



NOTE on the DETERMINATION of the FREE AOID 

 in SUPERPHOSPHATES. 



By F. B. Guthrie, f.i.c, f.c.s., and A. A. Ramsay. 



[Bead before the Royal Society of N. S. Wales, June 2, 1909.] 



Superphosphate in contact with grain is frequently found 

 to have an injurious effect upon its germinating power. 

 This is particularly the case when the grain is moist, and 

 McAlpine 1 has shown that the germinating power of wheat 

 is very considerably affected by bringing grain which has 

 been previously moistened with formalin or bluestone into 

 contact with superphosphate before sowing. This action 

 is undoubtedly due to the presence of free acid in the 

 superphosphate, and the object of the present experiments 

 is to test the methods by which the free phosphoric acid 

 can be determined by titration with soda, using different 

 indicators and by Thomson's and Glucksmann's methods. 2 



Summary of Results. 











Per cen1 



-, H 3 P0 4 



Gravimetrically 



. 



.. 



... 



.. 



94*84 



Titration with NaOH 



using 



different indicators — 





Methyl Orange . 







... 



. 



83*14 



Phenolphthalein . 



. 



.. 



... 



. 



88*18 



Litmus 











92*24 



Cochineal 





. 



.. 





82-87 



Thomson's method . 





.. 



.. . 



. 



92-32 



Glucksmann's method 



using 



*5 gm 



, in 250 



CC. ... 



90-18 



9? 



using 



*5 gm 



. in 500 



cc. ... 



89*32 



1 Agricultural Gazette of N.S. Wales, May 1906, p. 428. 



2 See Sutton, "Volumetric Analysis," 9th edition, pp. 113, 114. 



