208 ORIGIN OF THE NITRATES. 



Too strong a light checks it. Clayey substances and 

 porous matters appear to favour it, but it does not appear 

 that free nitrogen intervenes in this mode of formation of 

 saltpetre. 



6. Various questions here present themselves. Thus it has 

 been asked whether this slow oxidation is simply provoked by 

 the presence of clay and porous bodies, as occurs in Kuhlmann's 

 experiments, where the ammonia is changed into nitrous vapour 

 and nitric acid on contact with spongy platinum and oxygen at 

 about 300. 



Are the humus principles, the sulphuretted and ferruginous 

 compounds, and the other oxidisable bodies which are decom- 

 posed in the soil, at the same time that nitre is formed, the 

 medium of some special reaction ? 



Do they provoke the oxidation of the ammonia, becoming 

 oxidised themselves, as occurs with copper in presence of the 

 air ? Phosphorus does in fact exert an analogous reaction, and 

 this influence has also been attributed to humus. 



Does an oxidising body properly so called intervene, after the 

 manner of potassium bichromate and sulphuric acid, or of 

 manganese dioxide at a red heat, when the latter agent changes 

 the ammonia into nitrous vapour ? 



Does ozone play some such part, as held by Schonbein, 

 according to whom certain plants emit ozone, a substance, in 

 fact, capable of oxidising ammonia at ordinary temperatures, 

 with formation of nitrite. 



Lastly, do the mycoderms and microbes cause this oxidation 

 after the manner of a fermentation ? 



Such are the principal hypotheses which have been brought 

 forward since the eighteenth century up to our time to explain 

 the apparently spontaneous formation of nitre in nature. 



At the present day these questions, which have been for so 

 long a time the object of controversy, appear to have made a 

 decisive step forward in consequence of the recent experiments 

 of Schloesing and Mimtz. 1 



7. These investigators have found that the nitrification of 

 ammonia and the nitrogenous organic compounds takes place 

 under the influence of pointed, rounded, or slightly elongated 

 organised corpuscles, sometimes adhering in pairs of very 

 small dimensions, and very similar in appearance to the 

 corpuscular germs of bacteria. These corpuscles occur in all 

 arable soils and in sewage water, which they aid in purifying. 

 They cause the fixation of oxygen upon ammonia and nitrogenous 

 substances, generally forming nitrates, sometimes nitrites, when 

 the temperature is below 20 or the aeration insufficient. The 

 nitrites also result from the reduction of the original nitrates 



). 301, 1877; torn. Ixxxv. p. 1018; 

 torn. " 



1 "Comptes rendus," torn. Ixxxiv. p. 301, 1877; torn, 

 m. Ixxxvi. p. 892 ; torn. Ixxxix. pp. 891 and 1074 : 1879. 



