26 THE PHYSICAL PROPERTIES OF SOILS 



manner. With a graduated glass cylinder measure the 

 amount of water required to fill the brass cylinder level 

 full. 



CALCULATION 



Record all of the above weights in tabular form 

 and calculate the apparent specific gravity and the 

 weight in pounds per acre foot. Using the real specific 

 gravity found in the preceding exercise, calculate the 

 per cent of pore space in each soil by the formula 

 given by King, ''Physics of Agriculture," pp. 114-116. 



Discuss light and heavy soils, and the effect of tex- 

 ture upon the pore space. 



References : 



King, "Physics of Agriculture," pp. 114-116. 

 Snyder, "Soils and Fertilizers," pp. 12, 13. 



11. DETERMINATION OF PORE SPACE IN 



FIELD SOILS 



In order to determine the pore space in soils in place 

 in the field it is necessary to know the real specific 

 gravity and the weight of a given volume of the dry 

 soil. 



METHOD OF DETERMINATION 



With sampling tube (T) provided with a steel cut- 

 ting edge, collect samples from the field which will 

 represent the first and second foot of soil under dif- 

 ferent conditions, such as sod, cultivated field and stub- 

 ble land. The surface of the ground is leveled and the 

 sampling tube driven into the soil until the 12-inch 

 mark is exactly level with the ground surface. The 

 entire sampler is then dug out, a broad spatula or a 



