ACKNOWLEDGMENT. 



This investigation was carried out under the direction of Doc- 

 tor Ross Aiken Gortner. The author takes this opportunity to 

 express his appreciation and gratitude for the help extended during 

 the prosecution of this work, and for the unfailing kindness, 

 thoughtful advice and encouragement which was given. 



C. A. M. 



University of Minnesota. 

 Division of Soils. 

 January 1917. 



