Mar. 24. I9I9 Ammonification of Manure in Soil 317 



infusion determined by the above microscopic method. The infusion was 

 diluted to the desired strength and i cc. of it introduced into each flask. 

 The flasks were then incubated at room temperature and studied at specified 

 intervals. All flasks were controlled by uninoculated flasks as controls. 



The method used for the determination of the ammonia produced 

 was practically that of Potter and Snyder,^ which is an adaptation of 

 the Folin^ aeration method. A number of alternating Kjeldahl flasks 

 and absorption cylinders were set up in series so that a continuous cur- 

 rent of air could be passed through the system. Twenty-five-gm. 

 samples of the soils to be tested were placed in the Kjeldahl flasks and 

 200 cc. of N/30 hydrogen sulphate (HjSO^) were put in each absorption 

 cylinder. The flasks and cylinders were so connected that the air from 

 the end flask was driven over into its adjoining cylinder and absorbed 

 in the standard acid. Arranged in this way each Kjeldahl flask and 

 adjacent absorption cylinder with the cormecting tubes made one com- 

 plete unit and any number of these units could be connected in the series. 



When the apparatus was set up and all was in readiness for the aera- 

 tion, 2 gm. of sodium carbonate (NajCOg), and 50 cc. of ammonia-free 

 water were introduced into each Kjeldahl flask. The flasks were then 

 tightly stoppered, an^ the air was turned on at such a rate that about 

 6 liters of air per minute passed through the system. The aeration was 

 continued for about two hours and the standard acid in the absorption 

 cylinders titrated against N/30 sodium hydroxid (NaOH) to determine 

 the amount of ammonia driven off from the soil. Care was taken to 

 have the system absolutely air-tight and all rubber connections dry so 

 that in passing from the flasks to the cylinders none of the ammonia 

 would be absorbed by the water. Absorption in the standard acid was 

 aided by using Folin ammonia tubes to break up the bubbles of air when 

 they entered the absorption cylinders. 



The determination of the amount of free ammonia in soil has always 

 been a difficult one. The accuracy of the results obtained is somewhat 

 doubtful, as many of the protein substances present in soil are readily 

 broken up by the reagents used in determining the ammonia piesent. 

 Consequently the ammonia determinations in this series of experiments 

 can not be regarded as absolutely true determinations of "ammonia 

 production." Still other factors which might tend to destroy the accu- 

 racy of the determinations are, first, that the organisms themselves 

 might utilize the ammonia as rapidly as it is produced; and second, that 

 it might escape into the air. The latter is improbable because the 

 ammonia would be more likely to be absorbed by the water present in 

 the soil. Controls of sterilized manured soil were always run at the 

 same time as the inoculated soils, and in this way it was possible to 

 determine whether or not the organisms in the inoculated soil affected 

 the amount of ammonia production in any way. 



' Potter, R. S., and Snyder, R. S. the determination of ammonia in soils. Iowa Agr. Exp. Sta. 

 Research Bui. 17, 19 p., illus. 1914. 



' Folin, Otto, eine methods zur bestimmung des ammonl\ks im harne und anderen thierischen 

 PLUSSigkeitsn. In Ztschr. Physiol. Chem., Bd. 37, Heft 2, p. 161-176. 190a. 



