of Gases by Charcoal. 117 



and when the volume had been read off, the charcoal was intro- 

 duced, having been heated out of contact with air and plunged 

 into mercury while still red-hot. The residual volume was ob- 

 served after a lapse of about twenty-four hours. Of all the 

 charcoals I have examined, that made from the cocoa-nut has by 

 far the greatest absorbing power; its absorption for ammonia 

 being 17T7, and for cyanogen 107*5 times its volume. This 

 charcoal is very dense and brittle, and, when broken, the edges 

 have a semimetallic lustre. The greater number of the experi- 

 ments were made with this charcoal ; its pores are quite invisible, 

 and it absorbs scarcely any mercury during the cooling. The 

 numbers indicating the absorptions in general agree remarkably 

 well, particularly when the absorption is large. In one or two 

 cases, however, there are considerable differences in the several 

 experiments : this is most apparent with oxygen and phosphu- 

 retted hydrogen; these gases were most carefully examined, but 

 the results obtained always differed slightly; with oxygen this 

 is probably due to the formation of a variable quantity of car- 

 bonic acid, which is readily absorbed by the charcoal. I have 

 determined the absorption for some gases which had not previously 

 been investigated ; the principal of these are cyanogen and me- 

 thylic ether. 



The first of the following Tables contains 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 the level of the mercury; 



P, the barometric pressure in millimetres ; 



T, the temperature in Centigrade degrees. 



C, the volume of the charcoal in cubic centimetres. 

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

 3, &c. 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 charcoal gives 

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

 by one volume of charcoal in each experiment, and the second 

 column gives the means. 



These experiments were conducted in the laboratory of the 

 Queen's College, Belfast. 



