I’KEblDENT’s ADDRESS. 
I'J 
nitrogenous matter in soil will bo coufmod to matters near tlio 
surface ; the nitrates found in the subsoil, or in the subsoil 
drainage waters, have really been produced on the surface, and 
have passed down by diffusion, or in a descending column of water. 
Again, in arranging a filter-bed for sewage, it is obvious that when 
dealing with a lieavy soil lying in its natural state of consolidation, 
very little will Ijo gained by making the filter-bed of considerable 
depth. If, on the other hand, an artificial bod is to be constructed, 
it is clearly the top soil, rich in o.xidizing organisms, which should 
bo o.vclusively employed.” 
There are some indispensable conditions to nitrification which I 
have not yet mentioned ; namely, first, tlie presence of phosphoric 
acid, one of the essentials of organized life, thus fulfilling the 
(Jerman proverb : “ Ohne phosphor kein leben.” Another is the 
presence of lime, magnesia, or some salifiable base with which the 
nitric acid may combine. Wherever this condition was absent, it 
was found that the process of nitrification stopped. Another 
condition is a convenient temperature. The organisms appear 
either to die, or to lose their activity, at a very low temperature ; 
unless very low, however, their action is revived with a rising 
temperature. Their point of greatest activity seems to be at from 
about 80“ to 100“ Fahrenheit ; but at or near the boiling-point of 
water they are absolutely destroyed. Perfect drying, independent 
of temperature, also destroys them ; but thi.s condition of thing.s 
never arises in a soil naturally. Altogether we are able to gather 
some valuable practical lessons in agricultural science from the 
study of these facts. It is evident that soils differ very materially 
In their state of fertility, and much of this must depend upon 
their nitrifying poiver. For instance, garden soil ivliich has been 
frequently broken up and exposed to atmospheric influences, and 
liberally manured, is very rich in nitrifying power. On the other 
hand, cold clay soils, badly drained, and difficult to work, arc very 
deficient in this capacitj’’, as also are all soils in Avhich there is a 
want of phosphoric acid or lime. It is evident that, in the 
present state of practical agriculture, these matters must receive 
c 3 
