E. J. Russell and H. B. Hutchinson 



127 



difference as large as possible the soils were kept for some months : the 

 results are given in Table 4. 



When Soil 1 was put up it contained 119Q per cent, of nitrogen ; 

 during the 15 months the untreated soil has lost "009 per cent. In no 

 case does the toluened soil contain more nitrogen than the untreated : 

 the assumption that the increased productiveness of partially sterilised 

 soils is due to increased nitrogen fixation is therefore wrong. On the 

 contrary there appears to be an actually greater loss of nitrogen from 

 the toluened soil, and in two cases also from the heated soil than from 

 the untreated soil. 



§ 19. Humus. Since humus is a somewhat indefinite group of 

 substances the method of determinations must be arbitrary, but by 

 working under definite conditions it is possible to get comparable 

 results. The soil is washed with dilute hydrochloric acid till the 

 washings are free from calcium, then with water, finally it is shaken 

 with a 4 per cent, solution of ammonia to dissolve the humus. Deter- 

 minations are made of the total organic matter in the extract (humus), 

 and of nitrogen left after the ammonia has been boiled off (humic 

 nitrogen). 



Table 5. Changes in hiunus. 

 Soil 1, kept 15 months. 



Amount originally present 



After 15 months, untreated soil. 



Soil heated to 98°.... 



Toluene evaporated . 



Humus, 

 per cent, in soil 



1-06 

 •91 

 •93 

 •90 



Humic nitrogen, 

 per cent, in soil 



•047 

 •049 

 •043 

 •051 



Nitrogen in 

 humus, per cent. 



4.4 



5-4 

 4.7 



5-6 



The total amount of nitrogen is given in Table 4, Soil 1. 

 Soil 2, kept 10 months. 



The experimental error is rather large, and too much stress must 

 not be laid upon small differences, but so far as the figures have any 



Joum. of Agric. Sci. m 9 



