14 



THE PHYSICAL PROPERTIES OF SOILS 



a tight box. Take the samples to the laboratory, weigh 

 each box separately, remove the lid and expose the 

 contents to the air. Weigh at the end of three days 



"Vi UCvW-^ C\RCUIT 



TO "BKTTt.H^ OR 

 ^WUNT CIRCUIT 



DIAGRAM SHOWING THE CONNECTIONS FOR THE AUTOMATIC 

 CONTROL USED ON ELECTRICAL DRYING OVENS 



The Tube A is filled with alcohol or a calcium chloride solution and 

 placed inside the oven. D, the source of heat, is a series of lamps 

 or a coil of fine wire, also located inside the oven. As the temper- 

 ature increases the liquid in the tube expands. This expansion forces 

 the mercury up in the tube E until contact is made with the adjust- 

 able electrode V. This closes the circuit through the relay, and tiie 

 armature B is lifted. The heating circuit is broken in the mercury 

 cup at C, and the source of heat at U is shut off. As the oven cools 

 the mercury at E drops back and the relay circuit is broken, allowing 

 the armature B to fall and close the heating circuit. 



and at twenty-four hour intervals thereafter until 

 approximately constant weight is obtained. The loss 

 in weight is the capillary moisture. Note should be 

 made of the rainfall of the previous week and of the 

 weather conditions at the time the sanij^les were taken. 



