MICEOBES, OE BACTERIA. 121 



XL The Microbes which produce Saltpetre. 



It is known that nitre or saltpetre, i.e. potas- 

 sium nitrate, is produced in damp places where de- 

 composing animal matter is found in contact with 

 carbonate of potassium. It is found, combined with 

 other salts of iifne, soda and magnesia, in stables, sheep- 

 folds, cellars, in the neighbourhood of urinals, and 

 in the earth of some localities (Peru and Chili). Its 

 industrial importance in the manufacture of gun- 

 powder, etc., has led to its collection. Formerly it 

 was extracted from the plaster of old houses, or fi'om 

 artificial nitre works which combined conditions 

 favourable to its production. Nitrates are produced 

 by the gradual oxidation of the ammonia furnished 

 by animal excretions. For a long while it was supposed 

 that this oxidation was simply due to the influence 

 of porous bodies, such as earth and stone walls. Nitric 

 acid was produced, then nitrates of lime, potas- 

 sium, etc. 



The researches of Boussingault, Schloesing, and 

 others, have now taught us that this phenomenon of 

 organic chemistry is due, like many others, to the 

 vital activity of one or more species of microbe, 

 whose invariable presence in the natural or artificial 

 nitre-works has been ascertained. These microbes are 

 aerobics, i.e. they only live and work when in contact 

 with the oxygen of the air, from which they derive 



