THE GASES IN ROCKS 559 
though it be allowed that the water vapor, if it came in contact with 
the lava, would be absorbed. Capillary force seems quantitatively 
inadequate. 
To reach the critical pressure of water due to the hydrostatic col- 
umn, it is necessary to penetrate the earth to a depth of about 6,g00 
feet. At depths less than this, water passing into the vaporous condi- 
tion, in the neighborhood of hot volcanic conduits, at temperatures 
below the critical point, should leave behind more or less of the matter 
held by it in solution, since the condensation, and hence molecular 
attraction of the vapor for solutes, is less than that of the water. Thus 
even if vapor from underground waters should enter the lavas, as 
Daubrée has suggested, in the outer 6,900 feet of the earth’s crust, 
much of the chlorides, sulphates, carbonates, and silicates, dissolved 
in the water, would have been left behind. At depths between 6,g00 
feet and 25,000 feet, beyond which water cannot penetrate, owing 
to the closure of all pores by the pressure of superincumbent rock, 
mineral matter dissolved in the water would probably still remain 
in solution when the liquid passed into the gaseous state at the critical 
temperature, since the density of the gas is equal to, or greater than, 
that of the liquid. 
The lava, being under considerable pressure, may be supposed 
to occupy all the cracks and crevices in the adjacent rocks, except 
those of capillary dimensions. If, therefore, in the passage of under- 
ground water into vapor, preparatory to entering lavas in the outer 
6,900 feet of the earth’s crust, much of the dissolved mineral matter 
be deposited in the minute pores leading to the lava, they should 
quickly become sealed, preventing any further access, even of water, 
tothe lava. To test this principle experimentally, a cylinder of medium- 
grained Potsdam sandstone from Wisconsin, 4o millimeters in 
diameter and 28 millimeters in thickness, was soldered into a short 
piece of iron piping, fitted at one end with an elbow to serve as a 
receptacle for water, and at the other with a cork and a condenser. 
When ready, the receptacle was filled with Lake Michigan water 
and a Bunsen burner was placed so as to heat the sandstone cylinder 
within the iron tube. One side of the sandstone was thus kept at a 
temperature slightly above too°, while the other face, in contact with 
the water, remained just at the boiling-point. Water was found to 
