210 ORIGIN OF THE NITRATES. 



the nitrites, and change them into organic nitrogenous com- 

 pounds during the development of their mycelium. They act 

 in the same way upon ammonia or the ammoniacal salts, and 

 even by preference. Later on, during fructification, a portion 

 even of the nitrogen is eliminated in the gaseous form, some- 

 times with intermediate reproduction of ammonia. 



These observations, as a whole, show the existence of par- 

 ticular organised beings, analogous to the acetic ferment, which 

 cause the fixation of oxygen upon ammonia and nitrogenous 

 organic compounds, and consequently the change of these 

 substances into nitrates. They go far to resolve the problem of 

 nitrification, effected in nature at the expense of the nitrogenous 

 or ammoniacal compounds ; a problem, moreover, which is quite 

 distinct from the fixation of free nitrogen taken from the 

 atmosphere. It is, however, allied to it ; for natural nitrifica- 

 tion is effected upon already formed and pre-existing nitrogenous 

 compounds. 



2. CHEMICAL AND THERMAL CONDITIONS OF NITRIFICATION. 



1. These facts being admitted, it will be useful to show that 

 the study of the quantities of heat liberated during the act of 

 natural nitrification throw a fresh light upon the latter. In 

 order to render the discussion clearer, it will be best to attempt 

 at the outset to define the chemical conditions of this oxidation, 

 as far as can be done in the present state of our knowledge. 



2. The most developed experiments which have been per- 

 formed on the chemical conditions of nitrification are, even at 

 the present day, those of Thouvenel, although they date from 

 nearly a century ago. 1 They show that nitrification takes 

 place principally in connection with the gaseous compounds 

 produced in putrefaction, mixed with an excess of atmospheric 

 air. We know at the present day that the most important of 

 these compounds are ammonia, ammonium carbonate, hydro- 

 sulphide, hydrocyanide, and perhaps hydrocyanic acid. That 

 it requires the aid of moisture. That it is more easily effected 

 in the presence of the alkaline or earthy salts than in their 

 absence. Lastly, it hardly occurs save with carbonates, to the 

 exclusion of sulphates. For example, a basket pierced with 

 holes, and containing well-washed chalk, being placed over 

 blood in a state of putrefaction, the chalk was found after some 

 months to contain 2 -5 per cent, of nitrate. A plate, containing 

 washed mortar and placed in the atmosphere of a stable, con- 

 tains nitrates at the end of three weeks, etc. These conditions 

 agree with the biological conditions which preside at the 



1 "Me'moires de 1'Acade'mie des Sciences" (Savants Strangers), torn. xi. 

 1787. 



