29 



sample in the ball mill referred to above, making it into briquettes, 

 and testing them in the same way in which the rock samples are tested. 



Apparatus is now in preparation for making mechanical analyses 

 of gravel, which will doubtless prove of much value. These analyses 

 will consist in separating the natural sizes of the gravel by precipita- 

 tion in water. The present plan is to separate it into the following 

 sizes: Between 2 and 1 mm., 1.5 mm.; 0.5 to 0.25 mm.; 0.25 to 0.1 

 mm.; 0.1 to 0.05 mm.; 0.05 to 0.01 mm.; 0.01 to 0.005mm.; 0.005 to 

 0.0001 mm. 



The testing of paving brick will also be taken up during the present 

 fiscal year. 



Those desiring road materials tested must apply to Road-Material 

 Laboratory, Bureau of Chemistry, Department of Agriculture, Wash- 

 ington, D. C. 



