IG 
PRESIDKXT S ADDRESS. 
burnt sand and limestone, to ascertain wlietlier bunius or the 
organic matter of soil was necessary for the purification of sewage 
by soil. The sewage was passed through this pure mineral soil for 
twenty days quite unaltered ; but at the end of that time nitrates 
began to appear, and rapidly increased, until the filtered sewage no 
longer contained any ammonia, but nitrates only. The experimenters 
put to themselves the question : If the change was simply a matter 
of oxidation, why did twenty days elapse before it occurred 1 If, on 
the other hand, the seeding and growth of germs was necessary 
before the soil could become effective, the reason of the delay in 
nitrifying is apparent. Xow, one of the experimenters had proved 
beforehand that chloroform effectually suspends the action of 
organized ferments, while it has little or no action on soluble or 
chemical ferments. The vapour of chloroform was therefore allowed 
to pass through the filter, and immediately the formation of nitrates 
ceased. Nitrification had thus plainly been effected by some agent, 
the activity of which was destroyed by chloroform. The chloroform 
vapour was then removed, and the filtration of the sewage went on 
for some weeks, but no nitrification took place. The filtering 
material was then seeded with the washings of a rich garden soil in 
very small quantity, and the result was an immediate recurrence of 
nitrates, and the process ■went on as freely as before. The experi- 
menters therefore conclude from this instance, and from other 
cases of rapid nitrification, that oxidation is produced through the 
action of a living organism. 
Proceeding on these lines, a long series of most interesting 
experiments were commenced at the laboratory of the Eothamsted 
experimental farm, under the able supervision of Mr. Kobert 
'Warington, the results of which are published (On Nitrification : 
A Eeport of Experiments made in the Kothainsted Laboratory by 
Eobert Warington). 
Mr. Warington found that he could induce nitrification both in 
solutions containing ammonia, and in soils also containing it, both 
destitute of nitrates, by seeding them with a minute quantity of 
solution in which nitrification was known to be in progress, or from 
