rly in
eleven trials only one failure took place with soil from a depth of 3
feet. With clay soil from a depth of 6 feet success took place to the
extent of 50 per cent. No nitrification was obtained with clay from a
depth of 8 feet. Entire failure was experienced with chalk subsoil. The
process thus diminishes in activity the lower down we go.

[119] Koch has found that in soils he has examined few organisms were
found at a depth below 3 feet.

[120] See Appendix, Note VI., p. 198.

[121] For full analytical results see Appendix, Note VII., p. 198.

[122] We find the least amount in the month of April. In the water, from
a 20-and 60-inch gauge respectively, the amounts were 1.35 lb. and 1.61
lb. per acre (rainfall 2.25 inches). From then on to November the amount
steadily increases. In the latter month it reaches its maximum--viz.,
6.50 lb. (20-inch gauge) and 5.98 lb. (60-inch gauge) per acre (rainfall
2.30 inches). See Appendix to Chapter III., Note VIII, p. 160.

APPENDIX TO CHAPTER IV.

NOTE I. (p. 162).

OLD THEORIES OF NITRIFICATION.

According to the old theories, nitrification was regarded as a simple
case of the oxidation of nitrogen by the oxygen of the air, or by ozone.
The union of nitrogen and oxygen, however, probably takes place only at
very high temperatures, such as are formed during electric discharges.
It is needless to point out that the union of nitrogen and oxygen in
this way is not likely to occur in soils. According to other theories,
nitrification was effected by means of the oxidation of ammonia.
Ammonia, however, can only be oxidised to nitric acid by means of
certain powerful oxidising agents, such as ozone or hydrogen peroxide.
As, however, these substances are not found in the soil, it is much to
be doubted whether nitric acid is ever formed in the soil in this way.
It is possible, however, as held by some, that ferric oxide is capable
of inducing this conversion. On the whole, however, most evidence points
to the conclusion that all nitric acid produced in the soil is formed
through the agency of micro-organic life.

NOTE II. (p. 170).

The important fact that nitrification can take place in solutions
practically devoid of organic matter, was first shown by Dr J. H. M.
Munro ('Chemical Society Journal,' August 1886, p. 561). It was further
corroborated by Warington and P. F. Frankland. Winogradsky, however,
has carried out the most conclusive experiments on the subje