THE A WAKENING OF THE SEED 



37 





soil on top of it and tamp it down well with the blunt 



end of a lead- pencil; fill the bottle to the neck with 



water so that the spaces occupied with water and soil 



are about equal (the tamped-down 



layer is to prevent the water from 



penetrating the soil before we are 



ready). Insert a cork pierced 



with a wire (as shown in Fig. 33) 



and force the wire down so as to 



puncture the tamped layer (move 



it from side to side if necessary 



until the air begins to bubble up) . 



When the air has all risen, we can 



tell approximately how much was 



contained in the soil. 



When the method is under- 

 stood, we may dispense with the 

 cork and tamped-down layer and 

 proceed as follows : Take two bot- 

 tles of the same inside diameter; 

 fill both to the same height (half-full or less), one 

 with water, the other with the soil to be tested; pour 

 the soil slowly into the bottle containing water. If 

 the soil contains no air it should cause the level of 

 the water to rise to just twice the height at which 

 it stood originally; the amount by which it fails to do 

 this measures the amount of air in the soil. The 

 result depends somewhat on how tightly the soil was 



Method of determining 

 ■whether air exists in the 

 soil. 



