S68 HOW CROPS FKEB. 



jjhere (p. 107) indicate aLsorption Loth of oxygen and 

 nitrogen, as well as of carbonic acid. The fact that cliar^ 

 cx)al acts as an energetic oxidizer of organic matters lias 

 been alluded to (p. 1G9). Tliis action is something very 

 remarkable, altliough 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. Mattliias, Esq.), 

 and as is to be inferred from the Avell-known fact that the 

 odor of putrefying flesh, etc., cannot pa^s 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 di-y, moistened with pure water, or with 

 solution of caustic soda. (Experiments in Sheflield labo- 

 ratory, by Dr. L. H. Wood.) 



Putrefying flesh, covered w^ith charcoal as in Stenhouse's 

 experiment (p. 169) gives off ammonia, but no nitric acid is 

 formed. Dumas has indeed stated ( Comptes Rend.^ XXIIT) 

 that ammonia mixed with air is converted into nitric 

 acid by a porous body — chalk — that has been drenched 

 ■with caustic potash and is heated to 21r2° F. But this is 

 an error, as Dr. Wood has demonstrated. It is true that 

 platinum at a liigh 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. 

 Gh. V. Ph., loG, 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. Me- 

 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. But 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 Bendus, XLIY, 



