xii PREFACE TO THIED EDITION 



based largely upon the recent report of the Committee 

 of the Laboratory Section of the American Public 

 Health Association. 



Throughout the book we have resorted freely to 

 the use of tables of actual data for the illustration of 

 the various points discussed, believing that ample 

 familiarity with practical examples furnishes the only 

 sound basis for judgment in sanitary water exam- 

 ination. 



For the benefit of the student the chapters have 

 been sub-divided into sections with prominent headings 

 indicating the general topics under discussion. 



Massachusetts Institute of Technology, 

 Boston, Mass. 



American Museum of Natural History, 

 New York, N. Y. 



Feb. I, 1915. 



