PHYSIOGRAPHIC FACTORS 



167 



The hygroscopic coefficient is the moisture content, expressed 

 as a percentage of the dry weight, of a soil in equilibrium with an 

 atmosphere of known relative humidity. The value is difficult to 

 obtain with accuracy and is of little use to plant scientists. 



\\^' —Inner Cylinder 



I 



— Cutting Cylinder 



062 



FIG. 83. Sampler for obtaining undisturbed soil for determining volume- 

 weight, air space, and water holding capacity. A counter-sunk steel plate or 

 a block of wood placed on the cylinder prevents it from being battered 

 when driven into the soil with a sledge hammer. The inner cylinder (see Fig. 

 79) is removed with the sample (600 cc.) and is covered with tightly fitted 

 lids for transportation.— After Coiled 



