ABSORPTION. 31 



ABSORPTION. 



To determine how much gas might be reabsorbed after being expelled by 

 heat, it was thought desirable to use a rock capable of producing a large 

 volume of gas. For this purpose a diabase from Nahant, Massachusetts, 

 which yielded 13.9 volumes of gas, was selected. This material was heated 

 at full blast until the gas evolution had practically ceased, which required 

 about four hours; 182 cubic centimeters of gas were obtained. After allow- 

 ing the powder to remain in the vacuum overnight, it was removed and 

 still more finely pulverized in an agate mortar. It was then submitted to 

 forced heat, yielding an additional 20 cubic centimeters of gas in six hours. 

 On the third day the powder gave up but 1 cubic centimeter in four 

 hours. As practically all the gas available under these conditions was now 

 removed, the heat was turned off, and 132.01 cubic centimeters of this gas 

 (at 27.0 and 758 millimeters) immediately introduced into the combustion- 

 tube, which was allowed to cool. At the end of 43 hours 101.84 cubic 

 centimeters (at 20.0 and 750 millimeters) remained to be pumped out. 

 This being equivalent to 103.73 cubic centimeters at 27.0 and 758 milli- 

 meters, leaves 28.28 cubic centimeters as the volume of gas absorbed by 

 the powder. The material in the tube was now heated for 2$ hours, but 

 only 3.47 cubic centimeters could be extracted before the gas evolution 

 ceased. Of this, carbon dioxide constituted more than 85 per cent. There 

 still remain 24.81 cubic centimeters lost in the operation a loss which is 

 probably to be attributed to the oxidation of that quantity of hydrogen 

 to water by ferric oxide, while the tube was cooling. This water-vapor 

 being removed by the calcium chloride drying-tube, hydrogen could not 

 be again freed by the reverse reaction when the tube was reheated. The 

 carbon dioxide may be explained by carbonation of iron or calcium and 

 the subsequent decomposition of these carbonates when heated the second 

 time. 



In order to ascertain how much absorption there might be at ordinary 

 temperatures, 72 cubic centimeters of the remaining gas, from which the 

 carbon dioxide had been removed, since carbonation is a recognized proc- 

 ess, was allowed to stand in the tubes for eight days. At the end of this 

 time no appreciable quantity of the gas had been absorbed. From this 

 and the preceding experiment, it is quite evident that while rock material 

 may take up certain gases while cooling from a higher temperature under 

 special conditions, at ordinary temperatures absorption, if it goes on at 

 all, takes place very slowly. Reversible chemical reactions undoubtedly 

 play an important part in such absorption as takes place under changing 

 temperatures. 



Professor Dewar experimented with celestial graphite to ascertain its 

 absorbing power for certain gases. After exhausting the graphite of its 

 gases, dry carbon dioxide was drawn through the tube for twelve hours 

 at ordinary temperatures. The tube was then heated and about 1.1 vol- 

 umes of gas, containing 98.4 per cent carbon dioxide, pumped off. The 

 graphite on the first heating had given 7.25 volumes of gas, of which 91.8 

 per cent was carbon dioxide. Dry marsh-gas was next passed over the 



