STATES OF THE GASES. 



39 



The greater volume of gas from the fragments was taken to indicate 

 that a portion of the gas was lost in the process of pulverization. An 

 analysis of these figures reveals the fact that the difference in volume 

 was chiefly due to the deficiency of the combined portions in hydrogen, 

 instead of carbon dioxide, and that while there was also a slight loss of 

 the latter gas, there was a decided gain in nitrogen. 



Returning to the rocks, Tilden * is authority for the 

 statement that it does not make much difference in the 

 quantity of gas evolved, whether the material be taken 

 in chunks or in a fine powder. Instead of abandoning 

 the idea of cavities, he believed them to be very minute. 

 But this is approaching an alternative hypothesis; if 

 the reduction of the cavities is carried far enough to 

 intermolecular spaces practical occlusion is the result. 



Another objection to the theory of mechanically-re- 

 tained gases apparently exists in the slowness with which 

 the gas is liberated when the material is heated. Usually 

 about three hours and often a very much longer time is 

 required to expel the gas. Unless the gas from cavities 

 be assumed to escape by diffusion through the walls of 

 the inclosing mineral, instead of violently bursting its 

 confines, there is no reason why it should not come off 

 with a rush when the combustion-tube is heated rapidly 

 to redness. Some rocks, generally those yielding a mod- 

 erate quantity of gas in which carbon dioxide is the 

 principal constituent, often give up their gas quickly- 

 mostly -within the first 60 to 90 minutes, although the 

 generation continues for a longer time, before ceasing 

 altogether. But other varieties of rock, particularly 

 those noted for greater volumes, in which the percent- 

 age of hydrogen runs high, emit gas slowly and steadily 

 for three or four hours. 



These considerations led me to try a series of experi- 

 ments which should show how much gas actually could 

 be obtained from the opening of cavities alone. For this 

 purpose a crusher was devised (fig. 2), capable of pulver- 

 izing a rock specimen in a complete vacuum. Adopt- 

 ing the principle of the familiar steel mortar, this was 

 constructed in three pieces. The cylindrical cup in 

 which the rock material is crushed possesses an internal diameter of 7 

 centimeters and a depth of 9 centimeters. The walls are purposely 

 made thick and strong and the bottom is protected from the abrasion of 

 hard minerals by inserting a disk of hardened steel. Inserted in the walls 

 is a stopcock through which the apparatus is to be exhausted and the 

 gases later pumped out. A circular steel cap, or cover, provided with six 

 screws, whose sockets are depressed in the top of the cylinder, is intended 

 to make the chamber of the mortar air-tight. In the center of the cap- 



1 Tilden, Chem. News, vol. 75 (1897), p. 169; Proc. Roy. Soc., vol. 64 (1897), p. 453. 



1... 



FIG. 2. Apparatus for 

 specimens 



