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i>lR J. B. LA.WES AI^D PKOFESSOR, J. H GILBERT OR THE 
distribution, favoured by the action of the roots, and the increased activity in the 
interchange of moisture and air which must take place under such circumstances. 
Nor is it explicable how such large cniantities of nitric acid could have been produced 
as w^ould be required for the rapidly increasing growth of the Medicago saliva, and 
for the large amounts of nitrogen in it, if nitric acid had been the exclusive or even 
the main source of supply. 
5, Experiments on the Nitrification ofi the Nitrogen of Subsoils. 
In our paper in the ‘ Transactions of the Chemical Society ’ already referred to, we 
showed, in the case of some j^rairie land subsoils, that their nitrogen was susceptible 
of nitrification, and that when, after repeated extraction, the action became very 
feeble, or ceased, it was renewed on the soils being seeded by OT gTam of rich garden 
mould, which would contain nitrifying organisms. Considering, however, that from 
the cmcumstances of the collection and the transmission of those samples, the entire 
exclusion of comparatively recent organic residue from the upper layers was uncertain, 
it was decided to experiment in a similar way with some of the Hothamsted raw clay 
subsoils. Those selected were :— • 
1. A mixture of samples from the third to the twelfth depths of 9 inches each, that 
is representing the layer of 90 inches thick from 19 to 108 inches deep, from each of 
3 out of the 4 holes from which samples were taken on the wheat-fallow land from 
July 17-26, 1883. 
2. Similar mixtures from the third to the twelfth depths, from the samples taken 
from July 17-26, 1883, from the Trifolium repens, and from each of the two Vicia 
saliva plots, respectively. 
3. From holes opened specially for subsoil samples only, one on the wheat-fallow 
land, on May 7, 1886, and one on April 16, 1886, in a field where red clover had 
been sown with barley in rotation in the previous sprmg, but from which no crop 
had yet been taken. 
The first column of the next Table (X.) shows, for each of these samples, the 
percentage of total nitrogen calculated on the dry sifted soil, as determined by the 
soda-lime method; and the second column shows the quantity of already existing 
nitric-nitrogen per million of fine dry soil in each case. The other columns show the 
amounts of nitiic-nitrogen per million dry soil, as deteimined by Schlcesing’s method, 
in watery extracts made by the aid of the water pump, after successive periods of 
exposure under suitable conditions as to temperature and moisture. In the case of 
the wheat-fallow and leguminous crop subsoils, the results relating to which are given 
in the upper two divisions of the Table, they were each seeded by the addition of 
OT gram of rich garden soil after the first period of exposure and subsequent 
extraction, and again by the addition of 0'2 gram after the third period and 
extraction. These experiments, with the exception of the determinations of the total 
nitrogen, were made in the Hothamsted Laboratory by Mr. D. A. Louis. 
