E. J. Russell and H. H. Hutchinson 



113 



arc given. At the outset we may state that the soil employed in the 

 experiments was taken from an arable field and contained moderate 

 but not large amounts of nitrogen, organic matter, and calcium carbonate 

 (§ 14). Partial sterilisation was effected either by heating to 98° C. or 

 by addition of 4 per cent, of toluene, which at the end of three days 

 was allowed to evaporate by spreading out the soil in a thin layer for 

 as long as might be necessary. For convenience this soil is called 

 " toluene evaporated " to distinguish it from a third series where the 

 toluene was left in during the whole of the experimental period. 



50 



40 - 



2 30 



20 - 



^ 10- 





Toluene 



Bvavo''' 



ate<i 



Toluene left in 



Untreated soil 



12 



16 



20 



24 



days 



Curve 1. Amount of Ammonia in variously treated soils (Table 2). 



A fourth series consisted of untreated soils; a few experiments were 

 also made with soils heated to 125° C, at which temperature all 

 organisms are killed. After treatment the soils were moistened and 

 kept for definite periods in bottles stopped with cotton-wool at the 

 ordinary laboratory temperature. In these circumstances various 

 changes soon set in, and are dealt with below. 



I. The cJianges taking place in pai^tially sterilised soils. 



§ 2, (a) Ammonia. Curve 1 shows the amount of ammonia found 

 in the various soils at stated intervals after the moisture had been 

 added. In the untreated soil there is no accumulation of ammonia. 

 The " toluene evaporated " soil and the soil heated to 98° C. show 



8—2 



