of Nitrification ; with an Extension of it. 173 



Persons engaged in the production of nitre know well, 

 that earths taken from caves furnish nitrates by lixiviation, 

 and that earths, replaced in the same circumstances, yield 

 again, after eight or ten years, new quantities of saltpetre. 

 This fact cannot be denied; but some have attempted to 

 weaken its force, by the reflection, that in general the nitrous 

 materials are not completely deprived of their salts by the 

 washing to which they are subjected ; while these materials, 

 exposed again to the air, become dry, and as the water does 

 not evaporate except at their surfaces, it deposits there all the 

 nitre which it held in solution. This objection ^yould be of 

 weight, if it were true, that only a small quantity of nitre 

 could be obtained from materials which had been replaced ; 

 but it is well known that if earth from a cave has given by 

 the first lixiviation 100 parts of nitric acid saturated with the 

 different bases, the whole mass being returned to the same 

 place, will yield again, after eight or ten years, the nitrates 

 which represent the same quantity of acid. It is not, there- 

 fore, only the nitre which the materials have retained, which is 

 obtained by the second lixiviation ; but besides, and for the 

 greater part, what is formed anew upon replacing the earth 

 in the circumstances which had induced its first nitrification. 

 Moreover, the same materials twice lixiviated, returned again 

 to the same cave, will yield, after eight or ten years, the same 

 quantity of nitre which they furnished at each of the two 

 former "lixiviations; and the nitrification is perpetuated with- 

 out a limit, provided that the returned earth possess a suffi- 

 cient portion of the base, which commonly solicits the forma- 

 tion of the nitric acid, and absorbs that acid as it is produced. 



Lavoisier took from the quarry a great number of specimens 

 of chalk, at Roche Guyon and Mousseaux, and all when 

 washed yielded a small quantity of nitrate of potash, mixed 

 with much nitrate of lime. These specimens were frequently 

 taken at a distance of many hundred toises from any habita- 

 tion, and from parts of the rock exposed to the rain and all 

 vicissitudes ot weather; and he has drawn this consequence 

 from the facts related in his memoir : " the nitric acid does 

 not pre-exist in the chalk of Roche Guyon, but is formed by 

 the action of the air*." It is remarkable that this chalk was 

 often richer in nitre than the best nitrous soils. The quantity 

 of nitre, which any specimen contained, was found to depend 

 most upon its vicinity to the surface. As the organic re- 

 mains of these rocks do not retain their animal matter, no in- 



* Memniret Elraiigerct dc I' Academic dcs Sciences, xi. P. II. pag. .'565. 



fluence 



