72 THE GASES IN EOCKS. 



to serve as a receptacle for water, and at the other with a cork and a con- 

 denser. 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 100, while the other face, in contact with the water, remained 

 just at the boiling-point. Water was found to penetrate the porous cylinder 

 readily, evaporating and leaving its dissolved material within the mass 

 of the sandstone, and escaping as steam on the farther side. The rate at 

 which the water passed through the sandstone at the outset was not deter- 

 mined, but after 5 liters of lake water had been used, it was found that 

 129 cubic centimeters traversed the rock and were condensed in one hour. 

 The rate slowly fell as the experiment progressed. While the thirteenth 

 liter was being used, only 73 cubic centimeters passed through the sand- 

 stone per hour. It was evident that the pores were becoming clogged, 

 but to complete the experiment with Lake Michigan water, which contains 

 only 150 parts of solid matter per million, would have required too much 

 time. To hasten the process, a saturated solution of calcium sulphate 

 was substituted. This soon caused a marked slackening of the passage of 

 water through the rock, and doubtless would have sealed the pores com- 

 pletely, if allowed sufficient time. 



From this experiment, it appears certain that water, evaporating in 

 the pore spaces of a rock and escaping as steam, will leave behind what- 

 ever material is in solution, until the crevices become clogged and the 

 penetration of water ceases. This principle may be applied to the outer 

 6,900 feet of the earth's crust; in the superficial portion of this zone it 

 should be very effective, since the conditions more nearly approach those 

 of the experiment; in the lower portion of this belt, as 6,900 feet and the 

 critical pressure (as well as temperature in the neighborhood of hot volcanic 

 pipes) is approached, the density, and hence the solvent powers, of the 

 water-vapor approach those of the liquid. The vapor, also, should escape 

 less readily from the liquid at these depths, since the expansive force of 

 the vapor drives the water back along its path with more difficulty. Toward 

 the critical point of water, therefore, the application of this principle 

 becomes more uncertain, but it would seem to be operative also at these 

 depths, though more and more slowly as the critical point is neared. 



It might be objected that the passage of water into vapor, involving 

 the latent heat of steam, would keep the adjacent rocks cool and cause the 

 deposition to take place at the very contact where the hot lava could fuse, 

 and dissolve, the precipitated salts. But it is very doubtful whether the 

 vaporization of such a small quantity of water, taking place with the slow- 

 ness imposed upon it by the minuteness of the capillary pores, would keep 

 the contact rocks at a temperature below 365. The gap between 365 

 and 1100 is too great for there not to be a space, if of a few inches only, 

 at an intermediate temperature. It is also to be remembered that the 

 latent heat of steam diminishes with the pressure until, at the critical 

 point, it becomes zero. The testimony of the country rocks through 

 which a volcanic conduit has passed is that metamorphism has usually 

 progressed to some distance from the contact of igneous intrusion. In a 

 long-established volcano, where the rocks surrounding the conduit have 



