INTRODUCTION 9 



phates and American phosphates from 50-88 % of tricalcium phos- 

 phate. Moreover, it has been shown (14) that these phosphates are 

 even more soluble in citric acid than the majority of open hearth 

 fluorspar basic slags, and that they contain phosphate compounds 

 which are in many respects similar to those in open hearth basic 

 slags (20). 



It is thus a matter of great urgency to ascertain their precise 

 manurial value, as it is no exaggeration to say that the future of 

 agriculture and our national prosperity will be largely determined 

 by the extent to which suitable phosphates can be supplied at a 

 comparatively low cost. 



The problem is a big one, capable of attack from more than one 

 point of view. Useful results are likely to be secured by investigating 

 the effect of climatic conditions, particularly rainfall, on the avail- 

 ability of the rock phosphates. The question of soil conditions is 

 also of great importance in this connection. Rock phosphates for 

 example may prove a failure compared with superphosphate on a 

 chalky soil under dry conditions, whilst on a sour soil and under a 

 more humid climate the reverse may well be the case. 



