NOTES ON THE NATURE OF THE PHOSPHATES 

 CONTAINED IN MINERAL PHOSPHATES. 



By G. S. ROBERTSON, M.Sc. 

 {Easl Anglian Institute of Agriculture, Chelmsford.) 



The present work has been undertaken with tlic o])ject of ascertaining 

 the actual compounds of phosphoric acid and hnie present in rock 

 phosphates, a better knowledge of these compounds being of some 

 agricultural importance. 



The following table shows the analysis of the rock phosphates used. 



100-00 100-00 100-00 10000 100-00 100-00 100-00 



Each of the above phosphates was ground, and 5 grams submitted to 

 consecutive half-hour extractions with 500 c.c. of 2 per cent, citric acid. 

 The harder phosphates, such as Florida pebble phosphate and Makatea 

 Island phosphate, were separated into various grades of fineness by 

 means of the 1 mm. sieve, and sieves with 30, 60, 90 and 100 holes 

 to the linear inch. Five grams of each of the five portions so obtained 

 from both phosphates were submitted to five consecutive extractions 

 with 2 per cent, citric acid. By this means a large number of citric 

 acid extracts of these two rock phosphates were obtained. 



