PREFACE 



TO THE SIXTH EDITION. 



As about 27,000 copies of this little book have been 

 printed during the last ten years in England, the United 

 States, and Belgium, I am encouraged once more to do 

 my best to improve it, and to make such alterations and 

 additions as the progress of Agricultural Chemistry seems 

 to demand. 



The largest additions will be found in the chapters 

 relating to Manure, Animal Nutrition, Food, and the Dairy. 

 The new theory of the partial nutrition of leguminous 

 plants through their root tubercles has been adopted. The 

 isodynamic values now ascertained for the various con- 

 stituents of foods have also been introduced ; and for the 

 first time the comparative value of different foods, and the 

 ratio of the albuminoid to the non-albuminoid matter in 

 each food, have been calculated on the basis of these values. 

 The general aim of the book is, as before, to supply 

 students with a concise Handbook of Agricultural 

 Chemistry, describing the more important facts of the 

 science, and especially those having a practical bearing 

 on agricultural operations. To teach chemistry, or the 

 operations of practical agriculture, is not attempted. 



R. W. 

 February, 1891. 



