218 ORIGIN OF THE NITRATES. 



to evaporate the latter to obtain small quantities of nitrates. 

 Even in sudden oxidations, hydrogen, and the hydrocarbon 

 gases, burning in oxygen mixed with nitrogen, yield some traces 

 of the oxygen compounds of nitrogen. 



3. Ozone. Schonbein attributed the first formation to the 

 action of ozone, formed by phosphorus, on free nitrogen. Ozone, 

 he said, oxidises nitrogen in the cold, especially in presence of 

 water or alkalis ; its formation in the atmosphere would account 

 for the natural formation of nitric acid, which would reduce the 

 problem of the formation of the latter to that of ozone. 



But this theory has fallen in face of the experiments 

 separately by Carius and the author, 1 experiments from which 

 it results that pure ozone does not oxidise nitrogen in any way. 

 The assertions of Schonbein, according to which the evaporation 

 of water in presence of nitrogen is sufficient to cause the 

 combination of these two bodies and the formation of ammonium 

 nitrate, have likewise been found erroneous, since he seems to 

 have neglected the pre-existence of traces of nitrates in the 

 waters upon which he operated. 



It is none the less certain that the slow oxidation of phos- 

 phorus and the rapid combustion of hydrogen and the hydro- 

 carbon bodies develop nitrous compounds. But these are 

 exceptional reactions not sufficiently widespread nor efficacious 

 to account for the whole of the natural phenomena. 



4. Function of porous bodies. The same may be said of 

 Longchamp's theory, according to which nitrogen is absorbed in 

 presence of alkalis and porous bodies. The sole experiments 

 which have been cited in confirmation up to the present, are 

 those of M. Cloez, according to which a million litres of air, 

 directed during a period of time amounting to six months across 

 pumice-stone impregnated with potassium carbonate, yielded a 

 few milligrammes of nitrates. This quantity is too small for 

 its origin to be attributed with certainty to free nitrogen. The 

 least trace of nitrated compounds of mineral or organic origin, 

 not arrested by the purifying agents (acid and alkaline) in 

 passing across, perhaps even a trace of neutral and volatile 

 compounds, would be sufficient to account for such small 

 quantities of nitrates. Whatever be the interest of these 

 observations, there is therefore no certain conclusion to be 

 derived from them, so long as the conditions involve the 

 formation of traces of nitrates only. 



5. Nascent hydrogen. It has, in like manner, been supposed 

 that free nitrogen can be united to hydrogen, especially under 

 the conditions in which the latter is formed at the expense of 

 hydrogenated bodies. The formation of rust by the slow oxida- 

 tion of iron is especially cited with reference to this point. In 

 this formation traces of ammonia have been found. But these 



1 " Annales de Chimie et de Physique," 5 e se'rie, torn. xii. p. 440. 



