NECESSITY FOR ALKALINE MEDIA. 211 



development of the nitric ferment, as they have been defined 

 above. 



3. These various circumstances may also be accounted for 

 from the chemical point of view. We proceed to enter into 

 detail upon this subject. Ammonia and oxygen are, we have 

 said, the generators of the nitrates. Take, first, ammonia. The 

 liberation of gaseous ammonia, supplied by the slow transfor- 

 mation of nitrogenous organic principles, takes place only in an 

 alkaline medium. In an acid liquid it is clear that this 

 liberation cannot take place. 



Neither can it take place in a liquor capable of forming only 

 neutral and fixed ammoniacal salts by double decomposition, 

 such as the sulphate. 



On the other hand, it is facilitated when the liquor can give 

 rise by double decomposition to a volatile and partly dissociated 

 ammoniacal salt, 1 such as the carbonate. /The presence of a") 

 fixed alkali, or of an alkaline carbonate, is not only useful for 

 setting free the pre-existing ammonia of the ammoniacal salts ; 

 it further causes the generation of ammonia, at the expense of 

 the principal organic nitrates, in virtue of a sort of predisposing 

 affinity, owing to the intervention of the excess of energy 

 resulting from the saturation of the bases by the acids produced 

 during oxidation. Let us now turn to the latter phenomenon. 



Air, or rather its oxygen, is indispensable, because we are 

 here dealing with a phenomenon of oxidation incapable of 

 taking place in a reducing medium, such as a substance under- 

 going putrefaction. 



From the same point of view, the presence of an alkali, or of 

 a salt having an alkaline reaction, is very efficacious in accele- 

 rating the oxidation of organic principles by the oxygen of the 

 air, and at the ordinary temperature, while they offer much more 

 resistance in an acid medium. The mode itself in which the 

 oxidation of ammonia takes place during nitrification helps to 

 account for the efficacy of the fixed alkalies and their carbonates. 

 Now, the slow oxidation of ammonia develops nitrous, then 

 nitric acid, which must gradually combine with the portions 

 of free and non-oxidised ammonia. Hence, finally, results 

 ammonium nitrate, that is, a salt fixed at the ordinary tempera- 

 ture and devoid of alkaline reaction. If a nitrogenous principle, 

 taken by itself, were operated upon, half the ammonia would 

 thus be withdrawn from the oxidising action, and at the same 

 time the liquor would constantly tend to lose the alkaline 

 reaction due to the existence of free ammonia, a reaction which 

 facilitates oxidation. But the alkaline carbonate retains the 

 alkaline character, because it gradually transforms the nitrate 

 of ammonia into fixed alkaline nitrate and ammonium carbonate, 



1 "Essai de Mfoanique Chimique," torn. ii. p. 717. 



P2 



