CHEMICAL WORK. 137 



form other products, at the same time usually giving out carbonic acid as 

 a result of the plant's assimilation. The processes of oxidation and deoxi- 

 dation are carried on by them ; and it is a question whether, in the particular 

 cases mentioned on the preceding pages, the changes are not dependent on 

 the presence of microbes. They set sulphur free from sulphates (genus 

 Beggiatoa) ; make ammonia and nitrates {Micrococcus nitrijicans) , deoxidize 

 nitrates and other salts ; aid plants in taking up nitrogen through the roots ; 

 probably aid animals in their digestive processes, besides causing some of 

 their diseases ; they are the basis of all processes of fermentation, and 

 are concerned fundamentally in animal putrefaction and vegetable decay. 

 Tyndall proved that flesh would not decay if shut away from Bacteria — 

 the strong afiinities of its elements being unable to take a start without 

 help from these minutest of plants. The Bacteria are the smallest of 

 workers and among the largest of producers. 



In garden earth which is free from compost, as T. Leone found, the nitrification process 

 converts the nitrous acid into nitrate ; while, on adding compost, the nitrate is deoxidized, 

 and ammonia is given out ; or in gelatine or otlier proteid substance and water, the organic 

 substance is rapidly oxidized, attended by denitrification and the production of ammonia. 

 Bacteria liquify muscle and coagulated gelatine, and, according to Brunton and Mac- 

 fadyen, by producing a peptone-like solvent ; and the same kinds produce fermentation 

 in starch and similar non-nitrogenous carbo-hydrogen materials. 



This organic source of nitrates explains their occurrence in the earth of caverns, 

 or beneath sheds, and in other covered places ; also of the loosening of the sands of sand- 

 stones in such places — an agency that may in time cause a vast amount of degrada- 

 tion and removal. 



The native nitrate is usually either sodium or calcium nitrate, but sometimes 

 potassimn nitrate. The latter, which is salt-peter of the shops, is usually made from 

 the others. In Kentucky caves the calcium nitrate occurs, the caves being in limestone. 

 Sodium nitrate exists in the district of Tarapaca, northern Chile, over a great extent of 

 surface, 3300 feet above the sea, in beds several feet thick, which have a covering of earth 

 and a layer of gypsum, and contain some common salt. Moreover, underneath the bed 

 occur common salt, glauber salt, gypsum, magnesia alum, and large quantities of borates ; 

 all of which indicate deposits from hot springs or evaporated sea water. But the source 

 of the nitrate remains unexplained. This Tarapaca region of western South America is 

 much like the Great Basin of North America in position, dryness, and saline deposits. 



Mechanical Work of Chemical Products. 



In oxidation and other processes yielding solid products, particles of the 

 new material, when formed among the grains of the surface portion of a rock, 

 or in its rifts, act like growing wedges in loosening and detaching the grains, 

 and opening and extending rifts. The following figure represents a piece of 

 quartzyte from Canaan, Conn., divided up, or septated, by the oxidation 

 process. It looks like breccia, in which limonite is the cement ; and speci- 

 mens from the region were long so considered. But it was produced by 

 the formation and infiltration of limonite. The rifts were thus widened into 



