4 THE GASES IN ROCKS. 



tained gas (supposedly nitrogen) in a still more rarefied state, as its density 

 was 60 to 70 times less than that of the atmospheric air. Upon perforating 

 a cavity in a quartz crystal from Dauphine, an almost perfect vacuum was 

 discovered. Davy regarded the rarefied condition of the inclusions in the 

 crystals as strong evidence that the waters and gases did not penetrate 

 the crystals at ordinary temperatures and pressures. This he believed a 

 decisive argument in favor of the Huttonian, or Plutonian, school. How- 

 ever, a crystal from Brazil gave a very different result; an immediate 

 expansion to a volume 10 to 12 times greater than the original followed the 

 opening of a cavity. The composition of the gas was not determined. The 

 existence of compressed gas in the same sort of cavities seems adverse to the 

 conclusions which Davy based upon his earlier experiments, but he sought 

 to explain the difference by supposing the crust to have been formed under 

 a pressure more than sufficient to balance the expansion due to the heat. 

 Brewster 1 attacked the problem by observing the temperature at which 

 the inclosed liquid passed over into the gaseous state. A number of tests 

 showed this to range from 74 to 84 F. When raised to this temperature 

 the vacuity always reappeared. Brewster interpreted as follows : 



The existence of a fluid which entirely fills the cavities of crystals at a temperature 

 varying from 74 to 84 may be held as a proof that these crystals were formed at the 

 ordinary temperature of the atmosphere. 



For thirty years after Brewster the field was neglected until, in 1858, 

 Simmler 2 reviewed Brewster's work in the light of advancing scientific 

 knowledge. Studying the liquid inclusions in quartz, topaz, amethyst, 

 garnet, and other minerals, he arrived at the conclusion that the power of 

 expansion of the liquid in these inclusions showed it to be carbon dioxide. 

 Some years later Sorby, continuing the researches along the lines suggested 

 by Brewster and Simmler, found that the amount of expansion of liquid 

 carbon dioxide from C. to 30 C. corresponded closely to that observed 

 in the liquid of the sapphires with which he experimented. 3 In these sap- 

 phires it was noted that the liquid disappeared when warmed to approxi- 

 mately 30 C. As the critical temperature for carbon dioxide, above which 

 no amount of pressure will condense it to a liquid, is 30.92 C. (87.7 F.), 

 there remained little room for doubt that the gas was largely carbon 

 dioxide. Sorby remarked that this gas " might have been inclosed, either 

 as a highly dilated liquid or as a highly compressed gas; but since the 

 other 4 liquid has deposited crystals which dissolve on the application of 

 heat, it seems most probable that the water was caught up in a liquid 

 state, sometimes, perhaps, holding a considerable amount of carbon dioxide 

 in solution as a gas." 



In the same year Vogelsang and Geissler 5 heated quartz crystals and, 

 passing an electric spark through the gas thus liberated, examined its 



1 Sir David Brewster, Trans. Roy. Soc. Edinburgh, vol. 10 (1826), pp. 1-41 ; Edin. Jour, 

 of Science, vol. 6, pp. 153-156. 



2 R. T. Simmler, Pogg. Ann., vol. 105 (1858), pp. 460-466. 



3 H. C. Sorby and P. J. Butler, Proc. Roy. Soc., vol. 17 (1869), pp. 291-303. Earlier 

 papers by Sorby appeared as follows : Phil. Mag., 4th series, vol. 15, p. 152 ; Quart. Jour. 

 Geol. Soc., vol. 14 (1858), p. 453 ; Proc. Roy. Soc., vol. 13 (1864), p. 333. 



* Saline water. 



5 Vogelsang and Geissler, Pogg. Ann., vol. 137 (1869), pp. 56-75. 



