VI PREFACE 



sonable amount of work. The assistance of a trained 

 teacher will, of course, make the task easier. No one, 

 whatever his educational preparation, can hope to use 

 these or any similar methods successfully who can 

 not or will not follow instructions accurately and ex- 

 ercise patience in mastering every minute detail. 



In the preparation of this work, the writer has tried 

 to keep in mind the following points: (i) Accuracy, 

 simplicity and clearness of statement. (2) Making 

 prominent, as far as practicable, the reasons for each 

 step in each process. (3) Emphasis of common diffi- 

 culties and instructions for overcoming them. (4) Im- 

 pressing students with the necessity of precision and 

 care in performing . every detail given. (5) Selection 

 of the methods approved by experience. (6) Avoidance 

 of such technical methods as require unusual skill or 

 equipment. (7) Omission of unnecessary details. (8) 

 Embodiment of the results of the most recent investi- 

 gations. (9) The special needs of those for whose use 

 the work is designed. 



The scope of this work is far from exhaustive, but 

 the methods selected are given with necessary com- 

 pleteness. Chemical methods, requiring elaborate 

 equipment and extended special training, are purposely 

 omitted. Any one desiring a full description of such 

 methods can obtain it by addressing a request to the 

 U. S. Department of Agriculture, Bureau of Chem- 

 istry, Washington, D. C., asking for a copy of "Meth- 

 ods of Analysis adopted by the Association of Official 

 Agricultural Chemists." 



The methods that have been compiled here are in 

 large measure the direct result of the work of our 



