THE GASES IN ROCKS 551 
produced in this way from the non-gaseous constituents of the rocks. 
But these reactions were, in some instances at least, quantitatively 
inadequate to produce all the gas obtained. Quantitative experiments 
upon quartz and beryl indicated a considerable excess of hydrogen 
over what could possibly be produced from reactions involving the 
entire weight of iron salts in these minerals. Particularly striking was 
the case of a beryl from New England which expelled 150 times as 
much hydrogen as could be assigned to the interaction of steam and 
ferrous oxide under the most generous assumptions, and 37 times the 
maximum quantity possible from the total weight of iron in the mate- 
rial if it all occurred either as pyrite or in the metallic state. 
OCCLUDED GASES 
Such gas as was not held mechanically entrapped within cavities, 
nor originated from chemical reactions within the combustion tube, 
is assigned to that imperfectly understood phenomenon to which 
- Graham gave the name occlusion. Because the possibilities of obtain- 
ing gas from hydration and carbonation are much reduced in the case 
of freshly fallen meteorites, these bodies in some respects furnish the 
best conditions for studying the truly occluded gases. To obtain 
fresh material which had not been subject to hydration and carbona- 
tion, a fragment from the Allegan meteorite was obtained from the 
_ National Museum. This stone, which was gathered up still hot, 
within five minutes of its fall, and has not been subjected to outdoor 
_exposure, yielded somewhat more than half of its own volume of 
gas. Material from the interior of other meteorites yielded even 
more gas. 
In the case of rocks, the amount of occluded gases may be actually 
greater than that indicated by demonstrating the inadequacy of the 
other modes of holding gas to account for the total quantity extracted 
in the laboratory. But a determination of the exact proportion of 
- occluded gas in these cases would be difficult. In general, argon and 
helium, which do not enter into chemical combination, together with 
at least as much of the other gases as can be shown not to have been 
produced by chemical reactions, or the bursting of inclosing walls, are 
to be attributed to occlusion, or to some form of diffusion not distin- 
guishable from occlusion. 
