THE NITRIO XC\U OP THE SOIL. S67 



emallcr doses of lime or alkali than those employed by 

 Boussingault Avould have been found promotive of nitri- 

 fication, especially after the lapse of time sufficient to 

 allow the first rapid decomposition to subside, for then 

 we should expect that its presence would favor slow oxida= 

 tion. This view is in accordance with the idea, universally 

 received, that lime, or alkali of some sort, is an indispensa- 

 ble ingredient of artificial niter-beds. The point is one 

 upon which further investigations are needed. 



d. Free oxygen^ i. e., atmospheric air, and the porosity 

 of soil which ensures its contact with the jiarticles of the 

 latter, are indispensable to nitrification, which is in all 

 cases a process of oxidation. When sesquioxide of iron 

 oxidizes organic matters, its action would cease as soon as 

 its reduction to protoxide is complete, but for the atmos- 

 pheric oxygen, which at once combines with the protoxide, 

 constantly reproducing the sesquioxide. 



In the saltpeter plantations it is a matter of experience 

 that light, porous soils yield the largest product. The 

 operations of tillage, which promote access of air to the 

 deeper portions of earth and counteract the tendency of 

 many soils to " cake " to a comparatively impervious mass, 

 must also favor the formation of nitrates. 



Many authors, especially Mulder, insist upon the physic- 

 al influence of porosity in determining nitrification by 

 condensed oxygen. The probability that porosity may 

 assist this process where compounds of nitrogen are con- 

 cerned, is indeed great ; but there is no evidence that any 

 porous body can determine the union of free nitrogen and 

 oxygen. Knop found that of all the proximate ingredi- 

 ents of the soil, clay alone can be shown to be capable of 

 physically condensing gaseous ammonia (humus combines 

 with it chemically, and if it previously effects physical 

 condensation, the fact cannot be demonstrated). 



The observations by Reichardt and Blumtritt on the 

 condensing effect of the soil for the gases of the atmos- 



