12 



Physical characteristics of clays. 



When a sample of clay is sent to the laboratory to be tested the 

 following rules should be observed by the shipper. The sample should 

 not weigh less than 30 pounds in its air-dry condition, and it should 

 represent as nearly as is possible the average quality of the deposit from 

 which it is taken. The laboratory should be put in full possession of 

 such information as is available both as to the extent of the deposit 

 and the purpose for which the report is desired. In some cases it hap- 

 pens that the interest in a clay is centered in its ability to hold water, 

 for use in building canals or irrigation ditches. Clays vary as much in 

 their permeability as in other qualities, but it is manifestly a waste of 

 the chemist's time to investigate the firing qualities of a clay when 

 simple percolation tests are all that is necessary. 



Approved : 



JAMES WILSON, 



Secretary of Agriculture. 



WASHINGTON, D. C., July 25, 1904. 



ALLERTON S. CUSHMAN, 

 Chemist, Division of Tests. 



O 



