§ 107. THE PHYSICAL QUALITIES OF THE SOIL. 199 



4. The porosity of the soil, or the ratio between the 

 volume of the solid particles and that of the spaces in it 

 filled with air or moisture, is estimated by dividing the 

 apparent specific gravity of the soil, dried at 100°, by the 

 real specific gravity. Or if, for example, 2.5445 = the 

 real specific gravity of a certain soil, and 1.099 its ap- 

 parent specific gravity, then from the proportion, 



2.5445 : 1.099 = 100 : 43.2, 

 we get the volume of the solid particles in 100 parts of 

 the soil, and 100-43.2 = 56.8 = the volume of the pores. 



The porosity of the soil, just as it lies in the field, may 

 be estimated in a similar manner, by taking as the volume 

 of the soil the space that was occupied by the quantity 

 taken out to be weighed. 



To determine the volume occupied by the soil when 

 completely saturated with water, determine the volume 

 of 40-50 grms. of the air-dried, pulverized soil in a 

 graduated tube, that Avas filled with the earth in small 

 portions at a time, with occasional tapping on the table, 

 shake the soil up well with water containing 0.5° |^, of am- 

 nionic chloride ; then let the whole stand quietly, while 

 the solid particles collect together in the lower part of 

 the tube, and observe the volume occupied by this wet 

 soil. By dividing the second volume by the first, the re- 

 sult is put in a convenient form for comparison. 



e. Consistency, Tenacity, and Adhesive Power of 

 THE Soil. — The consistency of the soil when dry, its 

 tenacity, and the force with which it adheres to wood and 

 iron, are very important qualities ; but it is hardly jdos- 

 sible, by any of the methods in use for estimating them, 

 to get even approximately accurate results with small 

 quantities of soil. The following methods were devised 

 and used by Schiibler thirty years ago. 



1. To determine the consistency of the soil, or the 

 force with which its particles cohere together when dry, 



