PREFACE 



IN the companion volume in this series, entitled " Plant 

 Products," the chemical fertilizers are only treated from the 

 point of view of crop increment ; in the following pages it 

 is rather the sources and modes of manufacture of the 

 chemical fertilizers that take precedence. Nevertheless, no 

 trader can afford to ignore the aims of the purchasers of 

 the commodity he sells or leave out of account the ultimate 

 ends which his manufactures may fulfil. For this reason 

 some slight indication is given of the various purposes to 

 which the chemical fertilizers are applied, and some sug- 

 gestions are made on the better utilization of the materials 

 at our disposal for improving the produce of land. 



The last part of the volume describes some poisons used 

 to combat destructive insects and injurious parasites. 



As in the other volumes of the series, references are made 

 at the end of each section for consultation on matter alluded 

 to in the preceding text, whilst a General Bibliography 

 concludes the volume with a list of general works giving 

 information beyond the limits set for the survey in this 

 book. 



I have to thank Dr. A. A. Hall, Dr. G. C. Arnott, and 

 Mr. A. Spiller for much assistance in reading the proofs. 



S. HOARE COLLINS. 



February, 1920. 



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