PREFACE 



~p\URING the last century great and widespread changes have been 

 -*-^ made in agricultural practice — changes largely associated with 

 the increase in the use of artificial fertilisers as supplements to the 

 bulky organic manures which had hitherto been used. The value of 

 certain chemical compounds as artificial manures is fiilly recognised, yet 

 many attempts are being made to prove the value of other substances 

 for the same purpose, with a view to increase in efiiciency and decrease 

 in cost. The interest in the matter is naturally great, and agriculturists, 

 botanists and chemists have all approached the question fi-om their 

 different standpoints. In the following pages an attempt is made to 

 correlate the work that has been done on a few inorganic substances 

 which gave promise of proving useful in agricultural practice. Much 

 of the evidence put forward by different workers is conflicting, and it is 

 clear that no definite conclusions can yet be reached. Nevertheless, 

 examination of the evidence justifies the hope that results of practical 

 value will yet be obtained, and it is hoped that the analysis and 

 coordination of the available data put forward in this book will aid in 

 clearing the ground for those investigators who are following up the 

 problem fi-om both the academic and the practical standpoints. 



W. E. B. 



ROTHAMSTED. 



October 1914. 



