E. J. Russell and H. J5. JIutohinson 125 



The results for Soil 2 arc plotted on Curve 1 (p. 113). 



§ 1(J. The immediate effect ot" heating the soil to 95" C. or of 

 treating with toluene is to cause a small production of ammonia 

 amounting to about 3 to 5 parts per million of soil, and on standing 

 there is a further production, the extent of which depends on the 

 amount of water present. With 8 per cent, of water the action is slow 

 and the curve is linear, but when 17 per cent, is present the curve 

 characteristic of bacterial processes is obtained. Action is slow for a few 

 days, but by the ninth day it has become very vigorous and remains so 

 for a time ; then it slackens considerably. Soil which has been heated 

 to 125° C. (at which temperature all organisms are killed) behaves 

 altogether differently : after the first production of ammonia due to 

 heating there is no subsequent change. It is clear then that the 

 continuous formation of ammonia in the partially sterilised soil is due 

 to living organisms. 



Where toluene is left in the change is quite different ; even with 

 17 per cent, of water the curve is nearly linear. The action of micro- 

 organisms is in this case excluded, but any enzymes set free could 

 continue to bring about decomposition. 



The untreated soil differs from all the others ; there is no accumu- 

 lation of ammonia either with 8 or 17 per cent, of water, but there is an 

 increase in the amount of nitrate, and the sum of ammonia- and nitrate- 

 nitrogen shows a small gain amounting to 9 parts per million in 31 days 

 in Soil 1, and 4 parts per million in 23 days in Soil 2. It is known 

 that the nitrifying organisms only produce nitrates from ammonia; 

 these quantities therefore indicate ammonia that has been formed and 

 then nitrified. 



§ 17. Unstable nitrogen compounds. When soil is boiled at ordinary 

 pressure with water containing magnesia in suspension there is a steady 

 and continuous evolution of ammonia arising from the decompositon of 

 unstable nitrogen compounds. By working under definite conditions it 

 is possible to obtain comparable results; determinations made simul- 

 taneously with those recorded in Table 2 are set out below. The 

 immediate effect of toluene and of heat is to increase the unstable 

 nitrogen compounds, and is therefore something more than a simple 

 liberation of ammonia : there is not however as great a subsequent 

 accumulation of the unstable compounds. 



§ 18. Total niti'ogen. The net change in the amount of nitrogen 

 has alone been investigated : it is not at present possible to measure 

 the separate processes of fixation and loss. In order to make the 



