PRODUCTION OF NITRE AND NITRATES. 249 



According to M. Proust, the soil of certain localities in the neigh- 

 borhood of Saragossa is an inexhaustible mine of saltpetre. I have 

 myself seen, near Latacunga, a short way from Quito, upon a soil 

 formed of trachytic debris, a similar production of nitre taking place 

 as it were under my eyes. 



2d. On the coast of Peru, in the desert of Tarapaca, at a short 

 distance from the port of Iquique, and in an argillaceous soil of ex- 

 tremely recent formation, there are numerous stratified deposites of 

 nitrate of soda, analogous to, and perhaps contemporaneous with, the 

 deposites of common salt which are worked upon the same coast, in 

 the desert of Sechura, near the equator. This is, so far as I know, 

 the only instance of a nitrate being dug out of the bowels of the 

 earth as a mineral mass. The nitrate of soda of Tarapaca, reacr.es 

 Europe at the present time in large- quantities, and supplies the 

 place of nitrate of potash in many chemical processes. Various ex- 

 periments have also been made upon the value of the salt as a ma- 

 nure ; but at present these experiments have been very contradic- 

 tory, and further experience seems necessary before any definitive 

 judgment can be come to on the matter. 



3d. The greater number of the soils that are exposed to animal 

 emanations — heaps of rubbish proceeding from buildings that have 

 been long inhabited, the soil of stables, cow-houses, cellars, &c., 

 almost always contain a quantity of nitrates. In countries where 

 rain seldom falls, and where consequently these salts, which are ex- 

 tremely soluble, can accumulate in the soil, in Egypt, for example, 

 the ruins of ancient cities are at the present time true nitre-beds. 

 It is with the formation from nitre in such circumstances that we 

 feel particularly interested. The presence of the salt is frequently 

 proclaimed in our agricultural operations ; it is formed during the 

 preparation of our dunghills, in the midst of our cultivated fields, 

 and we discover it in the plants which we gather. We are by so 

 much the more interested in discovering its existence, and in ascer- 

 taining its mode of action, as in the actual state of our knowledge we 

 are still unable to say whether or no nitre is an auxiliary in the 

 phenomena of vegetation, and contributes to the production of the 

 azotized principles which enter into the organization of plants. 



To have nitrates formed, the presence of azotized organic matter 

 is not sufficient ; it is further necessary that this matter during its 

 decomposition be in contact with alkaline, calcareous, or magnesian 

 carbonates. It has been observed that rocks of a crystalline struc- 

 ture do not nitrify so readily when they are without the substances 

 which have just been named. The calcareous and magnesian rocks 

 which are most favorable to nitrification, under the influence of ani- 

 mal emanations and of vegetables in a state of decomposition, are 

 those which are the least coherent, or which are most porous, such 

 as chalk, tufa, &c. In those countries where the soil does not un- 

 dergo spontaneous nitrification, certain arrangements of circum- 

 stances, known to favor the production of saltpetre, are made : arti- 

 ficial i\itre-Deds are prepared. In the north of Europe where the 

 rocks are 'granitic, m a hut or shed uuilt of wood, a mixture is made 



