SELF-PURIFYING PROPERTIES OF THE SOIL. 297 



hydrogen which filled the neighbouring houses ; 

 yet, when filtered, such water had no smell at 

 all, and was commonly drunk by the inhabit- 

 ants. The sulphur of the sulphuretted hydro- 

 gen had been converted into sulphuric acid, 

 and thus the water was purified. 



We may learn from these most interesting 

 discoveries a highly important fact, namely, 

 that there is a most active process of oxidation, 

 or union with oxygen, constantly taking place 

 in the soil. Nitrogenous matters are carried 

 down into the soil, there filtering through 

 various loose materials, upon the surface of 

 which oxygen is supposed to be condensed, like 

 ammonia by charcoal, undergo oxidation, and 

 nitric acid is the result, which then combines 

 with the various salts and bases it meets with, 

 forming nitrates. What is very curious, is, that 

 the more organic matter is on the surface, the 

 more certainly will nitric acid be thus formed ; 

 it seems as if a certain excess of organic matter 

 favoured the process of its conversion into nitric 

 acid. The sulphur and nitrogen of organic mat- 

 ter being thus oxidized and rendered compara- 

 tively harmless, it appears probable that its 

 carbon is also oxidized, and forms in many 

 instances the sparkling carbonic acid gas which 

 we so familiarly know to abound in most spring 

 water. 



