268 HOW CROPS FEED. 
phere (p. 167) indicate absorption both of oxygen and 
nitrogen, as well as of carbonic acid. The fact that char- 
coal acts as an energetic oxidizer of organic matters has 
been alluded to (p. 169). This action is something very 
remarkable, although charcoal condenses oxygen but to a 
slight extent. The soil exercises a similar but less vigorous 
oxidizing effect, as the author is convinced from experi- 
ments made under his direction (by J. J. Matthias, Esq.), 
and as is to be inferred from tle well-known fact tuat the 
odor of putrefying flesh, etc., cannot pass a certain thickness 
of soil. But charcoal is unable to accomplish the union 
of oxygen and nitrogen at common temperatures, or at 
212° F., either dry, moistened with pure water, or with 
solution of caustic soda. (Experiments in Sheffield labo- 
ratory, by Dr. L. H. Wood.) 
Putrefying flesh, covered with charcoal as in Stenhouse’s 
experiment (p. 169) gives off ammonia, but no nitric acid is 
formed. Dumas has indeed stated ( Comptes Rend., X XII) 
that ammonia mixed with air is conyeried into nitric 
acid by a porous body—chalk—that has been drenched 
with caustic potash and is heated to 212° I’. But this is 
an error, as Dr. Wood has demonstrated. It is true that 
platinum at a high temperature causes ammonia and oxy- 
gen to unite. Even a platinum wire when heated to red- 
ness exerts this effect in a striking manner (Kraut, Ann. 
Ch. u. Ph., 136, 69); but spongy platinum is without ef- 
fect on a mixture of air and ammonia gas at 212° or lower 
temperatures. (Wood.) 
e. Presence of organic matters prone to oxidation. Ke- 
duction of nitrates to ammonia, etc., in the soil—As we 
have seen, the organic matters (humus) of the soil are a 
source of nitric acid. Dut it appears that this is not al- 
ways or universally true. In compact soils, at a certain 
depth, organic matters (their hydrogen and carbon) may 
oxidize at the expense of nitric acid itself, converting the 
latter into ammonia. Pelouze (Comptes Rendus, XLIV, 
