iv PREFACE 



crops makes some knowledge of the chemistry of gasoline 

 and carburetion important. Finally the animal is considered, 

 together with its food, digestion, and products. 



The references at the end of each chapter give the principal 

 sources of information used in the preparation of this text. 

 While the lists are by no means complete, they will be of 

 help for any who desire to pursue the subject further. 



The thanks of the author are due to the German Kali 

 Works, "La Hacienda," Great Western Sugar Co., Economy 

 Silo and Manufacturing Co., Chilean Nitrate Propaganda, 

 American Coal Products Co., C. Tennant Sons & Co., 

 American Cyanamid Co., and the Avery Co., for many 

 of the illustrations. Particularly is the author indebted 

 to Dr. M. B. MacDonald, Mr. F. P. Weaver, and Mr. 

 R. U. Blasingame for helpful suggestions, and to Messrs. 

 C. A. Smith and E. DeTurk for some of the drawings. 



C. W. S. 



State College, Pa., 1915. 



