PREFACE 



THE raw materials of Agriculture are often the waste 

 products of the other industries, and the produce of Agri- 

 culture again forms the raw material for other industries. 

 The following pages attempt to pick up the story of those 

 industrial waste products which are useful as fertilizers, 

 and carry it on through the soil and crops, until new 

 products are available for industrial uses. Among the 

 many plant products which are obtained from the soil, food 

 takes a high position as an industrial raw product, since 

 neither men nor horses could work without it. No particular 

 effort is made to give encyclopaedic completeness of informa- 

 tion, but the aim has been to give a fair conspectus of a 

 large subject, with an appended bibliography for those 

 who are able to pursue their studies further. Details of 

 analytical chemistry are not considered in this volume 

 unless the standard text -books named in the Bibliography 

 appear incomplete or unsuitable. The volume covers the 

 cycle from factory to fertilizer, from fertilizer to field, and 

 from field to factory once more. 



I have to thank Mr. A. S. Blatchford, M.Sc., for valuable 

 help in revising proof-sheets. 



S. HOARK COWJNS. 



February, 1918. 



