ABSORPTION. 



33 



TABLE 20. 



In this case, hydrogen has been restored somewhat more completely 

 than carbon dioxide. Both of them amount to approximately two-thirds 

 of the original volume of these gases. 



A third test was made with amphibolite, after an interval of four months. 



TABLE 21. 



The recovery is here more marked in the case of hydrogen than in that 

 of carbon dioxide. 



A fourth test was made with Keweenawan diabase from Houghton, 

 Michigan, after an interval of six months. 



TABLE 22. 



After reposing six months in a paper bag, this diabase gave as much 

 carbon dioxide, when heated, as it had in the first combustion; but less 

 than one-fifth as much hydrogen was evolved on the second heating. 



It is clear that an interval of time partially restores the gas-producing 



properties of these rock powders. For this phenomenon, there are two 



possible explanations. Either the first heating does not expel all of the 



gas contained in the rock, which, by some sort of diffusion or molecular 



3 



