SUBTERRANEAN GASES. 77 



SUBTERRANEAN GASES. 



The atmosphere is now being fed by gases which escape through out- 

 lets other than those of active volcanoes. Work in the shafts of many 

 deep mines in different parts of the world is often impeded by the exhala- 

 tion of gases from the rocks. This is, of course, familiar in the case of 

 organic rocks, such as coal, in which the decomposition of organic substances 

 is in progress. Reference is here made especially to gases escaping from 

 crystalline or other inorganic rocks. An exhalation of this kind is a 

 notable phenomenon in several of the mines in the Cripple Creek region of 

 Colorado, where nitrogen and carbon dioxide are poured into the workings 

 in considerable quantities when the barometer is low. 1 Two analyses of the 

 gas escaping into the Conundrum mine at Cripple Creek gave the following: 



1st: Carbon dioxide, 10.2; oxygen, 5.7; nitrogen, 84.1; total, 100. 



2d: Carbon dioxide, 8.3; oxygen, 10.2; nitrogen, 81.5; total, 100. 



No carbon monoxide, marsh-gas, or hydrocarbons were detected. 



The gas from the Elkton mine, which was analyzed by Dr. A. W. Browne, 

 of Cornell University, consisted of nearly the same gases as from the Con- 

 undrum mine: Water- vapor, 1.4; carbon dioxide, 14.7; oxygen, 5.6; nitro- 

 gen, 76.8; argon, 1.5; total, 100.0. Hydrocarbons, methane, and hydrogen 

 were absent. 2 The authors estimate that this gas may be considered to be 

 25 per cent of air, 59 per cent of nitrogen and argon, 15 per cent of carbon 

 dioxide, and 1 per cent of water-vapor. The gas apparently is derived 

 from greater depths than those at which it issues, since it is warmer than the 

 air of the mines, and since practically no gas was encountered in the oxidized 

 zone. They regard the outpouring as the last exhalation of the extinct 

 volcano, around whose neck the Cripple Creek mines are located. 



In some of the potash mines in the vicinity of Strassfurt trouble is caused 

 by the escape of combustible gas into the workings. According to Precht, 3 

 blowers of this gas once lighted have burned continuously for periods as long 

 as two months. An analysis of this gas by Precht shows it to be largely 

 hydrogen. His figures are: Hydrogen, 93.05; methane, 0.778; carbon dioxide, 

 0.180; carbon monoxide, trace; oxygen, 0.185; nitrogen, 5.804; total, 100.002. 

 This investigator believed that but little of the hydrogen could have come 

 from the decomposition of organic matter; instead, he sought a source for it 

 in the possible oxidation of ferrous chloride in the salt by water, according 

 to the reaction: 



6FeCl 2 + 3H 2 O = 2Fe 2 Cl 8 + Fe 2 O 3 + 3H 2 



This source of hydrogen is somewhat analogous to the production of the 

 same gas by the action of water upon ferrous compounds at high tempera- 

 tures, which has already been discussed, except that in the salt beds the 

 supposed action has taken place at the ordinary underground temperature. 

 But these gases coming from the sedimentary salt beds of the Upper Per- 

 mian represent, of course, gas merely restored to the atmosphere, and not 

 an original contribution to it. 



1 Lindgren and Ransome, Prof. Paper 54, U. S. G. S., pp. 252-270. 2 Loc. cit. 



3 H. Precht, Ber. Deutsch. Chem. Gesell., vol. 12 (1879), pp. 557-561. 



