198 Mr. Hall, Dr. Miller, and Mr. Gimingham. [Dee. 19, 
trials, whilst with that from lower depths only failures were recorded, 
‘except in the case of two samples from 30 cm. ‘The soil from Plot 4-2 
(400 lb. ammonium salts) from a depth of 10 to 15 cm. only set up nitrifica- 
tion twice in nine trials, whilst that from lower depths proved active in six 
and inactive in four cases. The soil from Plot 9 [with the same ammonium 
‘salts], from a depth of 10 to 15 cm., failed to induce nitrification in 11 trials ; 
with that from lower depths there were occasional successes. Soil from 
Plot 11-1, to which the largest quantity of ammonium salts is applied, 
mever caused nitrification, except in the case of one sample from a depth 
of 45 em., but the soil from Plot 14, which receives sodium nitrate instead 
‘of ammonium salts, induced a vigorous nitrification, except in the case of 
samples from depths of 105 and 135 cm., to which the nitrifying organisms 
are rarely likely to extend in heavy undisturbed grass land like that at 
Rothamsted. 
The nitrifying organisms were more frequently found in the soil from 
the lmed halves of the plots, though in the case of Plot 11-1 they were 
not detected in the upper layer. 
These experiments indicated that the nitrifying organisms were present 
only sparingly in the soils which had received large amounts of ammonium 
salts, and that they were less abundant the more ammonium salts had 
been used, but that whenever the acidity of the soil had been reduced by 
the comparatively recent application of lime, nitrification was more 
frequently set up. 
In order to verify these conclusions, two attempts were made to nitrify 
the soil itself in bulk. One or two kilogrammes of the moist soil, just 
as 1t came from the field, was spread out in a comparatively thin layer over 
water under a bell jar, so as to exclude dust and to maintain a moist 
atmosphere; after exposure in a dark part of the building during five weeks 
and two months respectively, the soils were rapidly dried and the amount of 
nitrates in them determined. The nitrates were also determined in another 
portion of the soil at starting, so as to ascertain the amount formed during 
the exposure under conditions favourable to nitrification. Of course, in 
sampling and manipulating such large quantities of material, it was 
impossible to prevent accidental introduction of the nitrifying organisms, 
but they would not affect the object of the experiment, which was to 
ascertain if the soils in their acid condition permit the nitrification 
process to go on. At the outset the soils were found to contain nitrates, 
but to a less extent than is usual. The quantities, however, varied from 
plot to plot with the amount of nitrogen supplied as manure; in one 
ease, for example, the soil of Plot 11-1, receiving 600 lb. of ammonium 
