Soil Organisms concerned in Nitrogen Cycle. 525 



It is apparent from these figures that the auximone fractions have the 

 power of increasing the rate of nitrification in culture solution. If organic 

 matter in general has the effect of depressing nitrification, the additions 

 made in these fractions are evidently too slight to produce any such 

 result. However, since the water extract of bacterised peat, a highly 

 organic solution, nitrifies so readily, an experiment was made to compare 

 the rate of nitrification in Winogradsky's solution with that in bacterised 

 peat extract containing an equivalent quantity of nitrogen, and also with 

 nitrification in a solution of ammonium humate containing an equal quantity 

 of nitrogen. The humic acid for the ammonium humate was extracted from 

 raw peat in the usual manner, purified by re-dissolving in ammonium 

 hydrate, and re-precipitating with hydrochloric acid twice over, finally 

 dissolving up in excess of ammonia, and then expelling the excess by 

 evaporation on the water-bath. The ammonium humate thus obtained 

 was dissolved in distilled water and the ammonia in an aliquot part 

 determined. The concentrated solution was then diluted until it contained 

 the same proportion of ammonia as Winogradsky's medium. The requisite 

 amounts of potassium phosphate and magnesium carbonate were added to 

 the flasks containing this solution. The bacterised peat extract was 

 prepared by making a concentrated extract, determining the nitrogen it 

 contained, and diluting until it contained the same proportion as 

 Winogradsky's medium and the ammonium humate, the phosphate and 

 base being added as before. A series of 30 flasks was prepared, as shown 

 in the Table below, and after inoculation and incubation for seven days 

 25 c.c. from each flask was analysed for nitric nitrogen. The whole set 

 was then re-incubated for a further period of seven days, when 10 c.c. of 

 each was again examined. The figures obtained are given in Table XII 

 (p. 526). 



Although the greater part of the nitrogen in the water extract of 

 bacterised peat occurs in the form of ammonium humate, it appears from 

 the above figures that this substance, in the pure condition, is comparatively 

 slowly nitrifiable, and even the addition of auximones, which increases the 

 rate of nitrification of the ammonium sulphate to an appreciable extent, 

 does not render that of ammonium humate equal to that of ammonium 

 sulphate alone. This is probably due to the depressing effect of the organic 

 matter, although the readily nitrifiable bacterised peat extract contains a 

 similar quantity. It follows that, in this extract, there must be some other 

 factor to be taken into consideration besides the ammonia content and the 

 auximone fraction thus far isolated. 



It appears most probable, from all the results obtained, that the methods 



