THE PHYSICAL PEOPEETIES OF SOILS 89 



been shown that the physical properties depend ultimately, 

 to a large extent, upon the size of the particles and amount 

 of the interspace. These therefore are the chief points to 

 be determined. 



In order to estimate the interspace without disturbing 

 the arrangement of the particles it is necessary to procure 

 samples of the soil in situ. A simple and convenient plan 

 is to use a metal box 6 inches square by 8 inches deep, 

 i.e., having a total capacity of one-sixth of a cubic foot. 

 The soil is first dug away from around a block of soil 

 having a surface area somewhat larger than that of the box ; 

 the latter is easily pressed down over the block till the 

 bottom is level with the surface, and then, by inserting a 

 spade underneath, it can be lifted up full of soil. The 

 weight of the contents of the box multiplied by six gives 

 the volume weight of the soil in pounds per cubic foot. 

 With a little practice duplicates can be drawn in this way 

 which approximate very closely in weight. 



After weighing, the sample may be taken from the box 

 and dried. The weight 1 of dry matter divided by the 

 weight of an equal volume 1 of water gives the apparent 

 specific gravity, and this divided by the true density 

 gives the volume occupied by the solid matter. The 

 weight of water in the sample is found by estimating the 

 loss on drying and the volume occupied by it is easily 

 calculated. The remainder of the space, not occupied by 

 solids and water, is empty, i.e., occupied only by air and 

 gases. 



The relative amounts of space occupied by solids, water 



1 When the cubic foot is employed as unit volume, it will be found 

 convenient to adopt the ounce avoirdupois as unit of mass. For 

 practical purposes the weight of a cubic foot of water maybe taken as 

 1,000 ounces (the actual weight is 996-458 ounces). The relation of 

 ounces per cubic foot is, therefore, almost exactly the same as grams 

 per cubic decimetre, 



