Mr. J. Hunter on the Absorption of Gases by Charcoal. 365 



to this part of the inquiry the present short paper is devoted. 

 It will be observed that while the numbers indicating the absorp- 

 tions agree remarkably well in many experiments, in others they 

 differ considerably. When the gas is largely absorbed, as in the 

 case of ammonia, by logwood charcoal, the absorption is extremely 

 rapid, and terminates in a much shorter time than when the entire 

 absorption is less. The variations in the amount of absorption 

 are probably due in part to the slight differences which must 

 exist in the pores of different pieces of the same charcoal, and 

 also to unavoidable differences in the heating of the charcoals in 

 each experiment. In order to determine the effect of long-con- 

 tinued heat on the absorbing power of the charcoal, I kept a 

 piece of boxwood charcoal at a strong red heat for upwards of an 

 hour, after which its absorption for ammonia was found to be 79, 

 while when heated in the ordinary way it was 85. In all these 

 experiments the charcoal was heated as nearly as possible to the 

 same temperature and for the same length of time. The ab- 

 sorption generally terminated at the end of about twenty-four 

 hours, so that it was not increased by allowing the charcoal to 

 remain longer in contact with the gas. Charcoals do not absorb 

 all gases in the same relative proportion : thus logwood has the 

 greatest absorption for ammonia, fustic for carbonic acid, and 

 ebony for cyanogen. 



In the first Table are given the data from which the amount 

 of absorption was deduced in each case. 



V = the observed volume of the gas in cubic centimetres ; 



D = the difference in level of the mercury; 



P = barometric pressure ; 



T = temperature, in Centigrade degrees ; 



C = volume of the charcoal, in cubic centimetres. 



The separate experiments are indicated by the numbers 1, 2, 

 and 3. The upper line in each contains the volume of the gas 

 before the introduction of the charcoal, together with the observed 

 difference in level, pressure, and temperature; the lower line 

 gives the volume, &c. after the absorption was completed. 



Table II. contains the absorptions corresponding to the expe- 

 riments in Table I. The first column under each gas gives the 

 volume of gas, reduced to 0° C. and 760 millims., absorbed in 

 each experiment, and the second column gives the means. 



This investigation was conducted in the laboratory of the 

 Queen's College, Belfast. 



