34 



THE GASES IN ROCKS. 



rearrangement, gradually prepares itself to come off when again heated, or 

 else the rock powder absorbs gases from the atmosphere. If the carbon 

 dioxide were derived from the decomposition, at high temperatures, of a 

 carbonate such as that of calcium, the oxide of calcium thus produced 

 would be likely to capture carbon dioxide from the air, though perhaps 

 this would be a slow process in a paper bag where the circulation of air was 

 comparatively limited. Also, if the hydrogen came from chemical reactions 

 between ferrous salts and water combined in hydrated minerals, the atmo- 

 sphere might have restored to these minerals some of the water which they 

 lost when first heated. It was thought that rehydration, if combined 

 water be a vital factor in the production of hydrogen, could be more readily 

 effected by placing the exhausted powder in water for a few days than by 

 wrapping it up in a paper bag for as many months. 



Accordingly, the Keweenawan diabase powder (No. 85) which origin- 

 ally gave 3.88 volumes, and after six months 1.92 volumes, was heated a 

 third time (a week later) with the evolution of very little gas. This powder, 

 after cooling in the vacuum, was taken out of the combustion-tube and 

 immediately placed in a flask filled with freshly distilled water. A stopper 

 being fitted into the flask, it was allowed to stand for 66 hours. At the 

 end of this time, the water was poured off, the powder quickly, but thor- 

 oughly, dried and put into the combustion-tube. When heated, this powder 

 gave off 0.79 volume of gas; but instead of being largely hydrogen, 67.72 

 per cent of this was carbon dioxide. Hydrogen amounted to only 14.69 per 

 cent, while carbon monoxide reached 15.06 per cent. An analysis of this 



gas gave: 



TABLE 23. 



This carbon dioxide could not have come from the air, but must have 

 existed within the material and must have withstood three successive 

 heatings in the combustion-tube. From a comparison of these figures 

 with the two previous analyses of the gas from this material, what is true 

 of the carbon dioxide would appear to be true of the hydrogen as well. 

 This experiment favors the conclusion, that the gas which is obtained from 

 a rock powder by a second heating after a period of time, is not due to a 

 process of selective absorption from the atmosphere, but rather to changes 

 which have been slowly taking place within the powder itself. 



However, the results of these experiments upon the absorption of gas 

 by rock powders at ordinary temperatures and pressures can not throw 

 much light upon the source of the gases, or how they came to be embodied 

 in the rocks, since the conditions under which the rocks were formed must 

 have been very different. While high temperatures, in general, tend to 



