476 
Agricultural Chemistry, 
variations of season, and of other coincident conditions of the 
growth and maturation of the crop. 
But, Baron Liebig in his criticisms equally ignores our facts, 
our observations, and our conclusions regarding them ! With a 
view of maintaining that the increase of produce obtained was 
not proportional to the supply of ammonia by manure, and con- 
sequently that the results of our own experiments demonstrated 
the contrary of that which he alleges we have concluded from 
them, Baron Liebig compares the increase by a given amount of 
ammonia in different seasons, without any reference either to the 
varying character of those seasons, or to the fact, that in recording 
the experiments of which he treats, ice had ourselves called par- 
ticular attention both to the actual variations, and to their influ- 
ence upon tlie results in question. Thus he selects for his pur- 
pose, results obtained in the several seasons of 1844, 1845, 
and 1846 ; and shows that in the last (1846), the increase ob- 
tained from a given amount of ammonia-salt in manure, was once 
and a half or twice as great as in the other cases. In reference 
to this very point we had said : — 
" It should be remem'berecl, however, that as the season of 1846 was more 
than usually favourable to the production of corn, any calculations founded 
upon the results of that year miyht lead to an over-estimate of tvhat the am- 
monia would produce in an average of years." — Jour. Hoy. Agr. Soc. Eng., 
vol. viii. jMi't 1, p. 247. 
Again, speaking of the total amount of ammonlacal salts 
added to one of our plots (10a), in six years, he says : — 
" But as the whole lOfiO lbs. was not added in one year, but in ])ortions 
during six years, the soil became each year richer in them than it was in the pre- 
ceding. There remained a residue from the previous year, which was annually 
increased by the portion newly added." — Principles, p. 95. 
He then, in direct contradiction to the evidence of our experi- 
ments, goes on to deduct from the amount of nitrogen supplied 
to the soil in each year, that amount which he supposes was con- 
tained in the increase of crop obtained by it ; he assumes that 
the remainder accumulates from year to year, as a residue in the 
soil, the amount of which residue, taken together with that of the 
salt newly added, is to be considered as the amount of ammonia- 
salts yielding the increase of any particular year. In this way, by 
brinsfing forward from year to year an assumed efficient residue, 
which our experiments prove did not exist, he calculates the 
increase of produce in the sixth year as due to 1592 lbs. of am- 
monia-salts ! — though 400 lbs. only was the amount added as 
manure in that year. In this way it is, he arrives at the conclu- 
sion, tiiat the produce for a given amount of nitrogen steadily 
diminished ! He says : — 
" But it is and remains nndenialhj certain, that the proportion of ammoniacal 
