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XLVr. On some Phccvomenn uli'ich take place in the 

 Formation of So Itpelrc. By M. Lcjn&champ*. 



Jln chemistry there are several theories which reason avows, 

 but which experience cannot aKvavs contirni. The th.'ory 

 which T am about to give ot" certain plicenomena that lake 

 place in the f'onnalion of saltpetre, is supported by facts 

 known to every chemist, and confirmed bv a great number 

 of experiments, all of which have been published by such 

 respectable authorities, and are in themselves so consonant 

 with our chemical doctrme, thai scarcely any objection can 

 be offered against them. 



When we reflect on the formation of saltpetre, and on 

 the formation of nitrates in genei j1, we ought to be much 

 surprised at the difficulties experienced in our own and 

 other northern climates in the manufacture of saltpetre ; 

 while in other (Countries, and particularly Spain and India, 

 the nitrate is produced on the surface of the ground, al- 

 though the inhabitants contribute no manual labour what- 

 ever to its formation. 



We must seek, therefore, for the cause of this phseno- 

 menon in the nature of the climate ; and we shall support 

 this assertion by experiments and well-ascertained facts. 



In India and Spain when the rainy season is at an end 

 the atmosphere becomes dry, and continues so during a 

 great part of the year; while in the North it is always hu- 

 mid, except when the cold is so severe as to precipitate part 

 of the water which it holds in solution. But as the dryness 

 of the' southern hemisphere has a different origin from 

 that of the northern, the phaencuTiena are also very diffe- 

 rent. In fact, the atmosphere being very warm seeks every 

 where for water to dissolve, and sucks it, as it were, from 

 the bowels of the earth ; but this water coming to the sur- 

 face of the soil, brinsjs with it the nitre which it held in 

 solution, and deposits it to be combined with the air. In 

 the North, on the contrary, not only is the air cold, but the 

 ground also : there is no evaporation, and the water re- 

 mains in its bowels; and when, in summer, the dryness 

 occasioned bv the heat tends to bring the water to the 

 surface of the earth, and brings the nitre which it held in 

 solution, fresh rains succeed and carry it down again to a 

 certain depth. 



In this way we can easily explain why the nitre which 

 we find in the earths of India and Spain presents itself at 



* YromJuurnal dc Phyiiquc, August 1809. 



the 



