328 
On the Rain and Drainage - Waters at Rothamsted. 
quently in considerable quantity, has been long known, the salt- 
petre of India is indeed produced in this manner. It is only, 
however, during the last few years that the mode in which 
nitrification takes place has been clearly ascertained. Nitrifica- 
tion is the work of a living ferment contained in the soil, which 
is capable of oxidising ammonia, and probably other nitrogenous 
bodies, into nitric acid ; the action is, in fact, quite similar to 
that of the vinegar ferment, which oxidises alcohol into acetic 
acid. The investigation establishing this fact we owe to 
MM. Schloesing and Miintz ; their results have been amply 
confirmed by experiments made at Rothamsted.* 
The nitrifying ferment is apparently present in all fertile 
soils ; it requires for its activity a sufficient supply of water and 
air, and also some salifiable base, as chalk ; a certain degree of 
warmth is also necessary. No nitrification will take place in a 
dry soil ; the production of nitrates will increase in activity as 
the soil becomes wetter up to the point at which the water begins 
to interfere with the free aeration of the soil. Nitrification is at 
a standstill near the freezing-point, and gradually increases in 
activity as the temperature rises, reaching its maximum of 
energy about 98° Fahr. (37° C), At a higher temperature it 
diminishes in activity, and ceases altogether at 131° (55° C). 
The process of nitrification is probably chiefly confined to the 
surface soil, where nitrogenous matters are most abundant, and 
the supply of air greatest : it will proceed with greatest energy 
in summer time, and be especially active during a wet summer. 
The nitrate produced in soil is chiefly nitrate of calcium. 
When rain-water falls upon a soil it dissolves some of the 
ingredients which the soil contains, and these dissolved matters 
finally appear to a greater or less extent in the drainage-water. 
The substances dissolved by rain may be divided into two 
classes — 1. Substances freely diffusible within the soil ; 2. Sub- 
stances for which soil exerts more or less attraction, and which 
are therefore not freely diffusible. The acids freely diffusible 
are hydrochloric, nitric, and to a less extent sulphuric acid. 
The most readily diffusible bases are soda and lime. The 
chlorides and nitrates of sodium and calcium, and, to a less extent, 
the sulphates, are thus readily diffusible salts, and may be easily 
extracted from a soil if sufficient water be applied. On the 
other hand, most fertile soils possess a great retentive power for 
phosphoric acid, ammonia, and potash, and these substances are 
consequently only found in drainage-waters in minute quantity, 
except under very special circumstances. In the case of such 
* Schloesing and Miintz'a investigations will be found in the Comptes Bendus, 
Ixxxiv. 301; Ixxxv. 1018; Ixxxvi. 892; Ixxxix. 891, 1074; and the Rothamsted 
Papers in the Jour. Chem. Soc. 1878, 44 ; 1879, 429. 
