INFLUENCJE OF AIE-DKYING. 13 



EXEKCISE VII. 



THE I.NfPLUEKCE OF AIE-DRYING ON THE AMMONIFYING 

 POWEE OF SOIL. 



1. Divide some fresh, fertile soil into two portions. 

 Place one portion in an air-tight receptacle and keep it in a 

 cool place. Spread out the other portion, in a thin layer, 

 in a '\^'arm room to facilitate air-drying. Weigh the air-dry 

 soil, calculate the amount of moisture lost and restore it. by 

 the addition of sterile water. 



2. Weigh, off two 100 gram portions each of the fresh soil, 

 and of the air-dry soil that has been restored to its original 

 water content. 



3. Add to each soil portion 5 grams of dried blood and 

 stir with a sterile spatula. 



4. If necessary increase fl-ater content to optimum by the 

 addition of sterile water. 



5. Cover, and incubate for 7-8 days at 20° C. 



6. Determine the amount of ammonia formed by distill- 

 ing and titrating in the usual way. 



