548 R. T. CHAMBERLIN 
pares itself to come off when again heated; or else the rock powder 
absorbs gases from the atmosphere. ‘To exclude atmospheric absorp- 
tion this Keweenawan diabase powder, which originally 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 three 
days. At the end of this time, the water was poured off, the powder 
quickly, but thoroughly, dried, and put into the combustion tube. 
When heated, this powder gave off .79 volumes of gas, of which car- 
bon dioxide constituted 67 per cent. This carbon dioxide could not 
have come from the air, but must have existed within the rock material 
and must have withstood three successive heatings in the combustion 
tube. This experiment favors the conclusion that the gas which 
is obtained from a rock powder by a second or third heating after a 
period of time, is due, not so much to a process of selective absorption 
from the atmosphere, as to changes which have been slowly taking 
place within the powder itself. 
STATES IN WHICH THE GASES EXIST IN ROCKS 
In order to explain the immediate source of the gases obtained by 
heating rock material in vacuo, three different hypotheses naturally 
present themselves. ‘The simplest of these is to suppose the gases 
to exist in minute cavities or pores, having been entrapped within the 
rock during the process of solidification. This supposition is sug- 
gested and supported by the observation that microscopic slides of 
some minerals, notably quartz and topaz, reveal numerous small 
gas-bubbles. But while there is evidence that some gas is thus held 
in cavities, there is equally strong evidence to show that the greater 
part of it cannot be attributed to this source. 
To escape the difficulties encountered by the first hypothesis, 
appeal is made to the imperfectly understood property of some of the 
elements to “occlude,” or dissolve within their mass, certain gases. ~ 
It is remembered that under the proper conditions palladium will 
occlude goo times its own volume of hydrogen, and that the same gas 
is also absorbed, in lesser degree, by other metals, particularly plati- 
