THE AMMONIA OF THE SOIL. 239 



to agricultural vegetation only after tlieir incorporation 

 Avith the soil. 



Rain and dew are means of collecting tliem from the 

 atmosphere, and, as Ave shall shortly see, the soil is a 

 storehouse for them and the medium of their entrance into 

 vegetation. 



This is therefore the ])roper place to consider in detail 

 ilie origin and f )rmation of ammonia and nitric acid, so 

 far as these points have not been noticed when discussing 

 their relations to the atmosphere. 



Ammonia is formed iu tlic Soil either in the decay of 

 organic bodies containing nitrogen, as the albuminoids, 

 etc., or by the reduction of nitrates (p. 74). The former 

 process is of universal occurrence since both vegetable 

 and animal remains are constantly present in the soil ; the 

 latter transformation goes on only under certain condi- 

 tions, which will be considered in the next section (p. 

 269). 



The statement that ammonia is generated from the free 

 nitrogen of the air and the nascent hydrogen of decom- 

 posing carbohydrates, as cellulose, starch, etc., or that set 

 free from water in the oxidation of certain metals, as iron 

 and zinc, has been completely disproved by Will. (Ann. 

 d. Ch. n. Ph., 4.5, pp. lOG-112.) 



Tlie ammonia eiicountei-ed in sucli experiments maj' liave been, 1st, 

 tliat pi-e-existini^ in the pores of tlic substances, or dissolved in the wa- 

 ter ()i)erated witli. Faraday {Researches in Chemistry and Physics, p. 143) 

 has shown by a series of exact experiments tliat numerous, we may say 

 all, porous bodies exposed to the air have a minute amount of ammonia 

 adheriu;^ to them ; 2d, that which is generated in the process of testiu;^ 

 or experimenting (as when iron is heated with potash), and formed by 

 the action of an alkali on some compound oF nitrojien occurring in the 

 materials of the experiment; or, 3d. that which results from tlie reduc- 

 tion of a nitrite formed from free nitrogen by the action of ozone (pp. 

 77-83). 



Tlic Ammonia of the Soil. — a. Gaseous Ammonia as 

 Garhonate. — Doussiugault and LcAvy, in their examination 

 of the air contained la the interstices of the soil, p. 219, 



