386 L. D. BUSHNELL 



37°C. From the shakes we could detect the presence of anae- 

 robes, and plates showed the presence of aerobes. After we be- 

 gan the use of the present apparatus no contamination has been 

 noted and we were always able to culture the anaerobe if growth 

 had occurred. 



Samples were also taken for the determination of ammonia, 

 amino-acids and volatile fatty acids. 



Ammonia determinations. The ammonia determinations were 

 made by distilUng in the presence of magnesium oxide. At first 

 we tried the aeration method but even after eight hours we were 

 able to obtain tests for ammonia with Nessler's reagent. After 

 the gas analysis was made there was insufficient time for the aeration . 

 It has been found in this laboratory, in working with fermenting 

 mixtures of soil, etc., that there is a close correlation between 

 duplicate samples run by the aeration and distillation methods. 

 With small amounts of ammonia, the distillation methods, usually 

 gave somewhat higher results than the aeration method; while 

 with large amounts of ammonia present the results were reversed. 

 When small amounts of ammonia (10 to 20 mgm. per 100 grams 

 soil) were present the distillation method gave 3.G per cent more 

 ammonia than the aeration method. "N^Tien large amounts of 

 ammonia (60 to 75 mgm. per 100 grams soil) were present the 

 aeration method gave 4.0 per cent more ammonia then the distil- 

 lation method. 



Amino-acid determination. Amino-acids were determined by 

 the Van Slyke method. These determinations were complicated 

 by the presence of very large amounts of ammonia. Van Slyke 

 (1911) recommends the following method for the removal of 

 ammonia: The ammonia can be removed bj' distillation with 

 Ca(0H)2 under diminished pressure, using a 10 per cent suspen- 

 sion until a slight excess is present, as shown by turbidity and 

 alkaline reaction of the solution. The apparatus is evacuated to 

 30 mm. or less of mercury, and distillation continued for one- 

 half hour at 45 to 50°C. Alcohol is added to prevent foaming. 



We were unable to use this method because of lack of time and 

 the difficulty of removing all the ammonia from the medium, 

 As large amounts of ammonia were present and the temperature 



