32 



THE GASES IN ROCKS. 



powder for twelve hours; upon heating, only 0.9 volume, containing 94.1 

 per cent carbonic acid, was obtained. The same experiment repeated with 

 hydrogen gave only 0.17 volume, in which carbon dioxide reached 95 per 

 cent. 1 From these figures it would seem that absorption is not very im- 

 portant. The steadily decreasing volumes of gas with each successive 

 heating show the difficulty with which the gas is expelled, for apparently 

 it is liberated more readily after an interval of time than if reheated im- 

 mediately. Hence, unless the material used be completely deprived of its 

 gas, there is always a danger in assigning to absorption what may, in reality, 

 be only the last portions of the original gas. 



Wright used another method in testing the hypothesis that the gas 

 obtained from meteorites has been derived from our atmosphere by a 

 process of absorption. He believed that if the gas be due to absorption 

 from the earth's atmosphere, a meteorite should have stored up more of 

 it after being exposed for a considerable period than shortly after its fall. 

 His original analysis of the gas from a meteorite which fell in Iowa County, 

 Iowa, on February 12, 1875, was made a short time after its fall. A year 

 later, to extract the same quantity of gas from another fragment of the 

 same meteorite required not only a longer time than in the first analysis, 

 but more intense heating as well. 2 If any difference actually existed, a 

 loss rather than a gain was indicated in this interval. 



To test the effect of air exposure on a rock powder which had previously 

 been heated until the gas evolution had completely ceased, the exhausted 

 powders of my investigation were kept stored in paper bags, and several 

 of them were reheated after intervals of some months. Two analyses of 

 the iron basalt from Ovifak, Greenland, made 10 months apart, were as 



follows: 



TABLE 19. 



This basalt yielded about one-third as much carbon dioxide after the 

 interval as it did when originally heated, but the hydrogen in the second 

 portion of gas was almost a negligible quantity. 



A second test was made with a chloritoid schist from the Black Hills, 

 after an interval of more than a year. 



1 Sir James Dewar, Proc. Roy. Inst., vol. 11 (1886), p. 547. 



2 Wright, A. W., Am. Jour. Sci., vol. 11 (1876), p. 262. 



