266 HOW CROPS FEED. 
III. 1000 grms. of soil and 500 grms. marl acquired 0.002 grms. ammonia and 
0.360 grms. nitric acid. . 
IV. 1000 grms. of soil and 2 grms. carbonate of potash acquired 0.015 grms. 
ammonia and 0.290 grms. nitric acid. 
V. 1000 grms. of soil and 200 grms. quicklime acquired 0.303 grms. ammonia 
and 0.099 grms. nitric acid. 
The unfavorable effect of caustic lime is well pronounce- 
ed and is confirmed by other similar experiments. Car- 
bonate of potash, which is strongly alkaline, but was used 
in sma!l quantity, and marl (carbonate of lime), which is 
but very feebly alkaline, are plainly inferior to sand in 
their influence on the development of nitric acid. 
The effect of lime or carbonate of potash in these ex- 
periments of Boussingault may, perhaps, be thus explain- 
ed. Many organic bodies which are comparatively stable 
of themselves, absorb oxygen with great avidity in pres- 
ence of, or rather when combined with, a caustic alkali. 
Crenic acid is of this kind; also gallic acid (derived from 
nut-galls), and especially pyrogallic acid (a result of the 
dry distillation of gallic acid). The last-named body, 
when dissolved in potash, almost instantly removes the 
oxygen from a limited volume of air, and is hence used 
for analysis of the atmosphere.* 
We reason, then, that certain organic matters in the 
soil of Bonsdcuees garden, became ¢o altered by treat- 
ment with lime or carbonate of potash as to be susceptible 
of a rapid oxidation, in a manner analogous to what hap- 
pens with pyrogallicacid. Dr. I. Angus Smith has shown 
(Jour. Roy. Ag. Soc., XVII, 456) that if a soil rich in or- 
ganic matter be ade alkaline, moist, and warm, putre- 
factive decomposition may shorily set in, This 1s what 
happens in every we!l-managed compost of lime and peat. 
By this rapid alteration of organic matters, as we shall see 
(p. 268), not only is nitric acid not formed, but nitrates 
added are reduced toammonia. It is not improbable that 
* Not all organic bodies, by any means, are thus affected. Lime hinders the 
alteration of urine, flesh, and the albuminoids. 
4 
