GASES ABSORBED BY CHARCOAL. 2^3 



tube with this gas, which I had extraded from powdered mar- Carbonic acid 

 ble by vitriolic acid. I placed the incandefcent charcoal in the sa^« 

 machine which effe6led an abforption of lixteen inches fix lines, 

 that is to fay, of eleven twelfths of the capacity. This ex- 

 periment correfponds exactly with that which I made with the 

 tube of twelve inches in height, and one inch in diameter, and 

 in which the charcoal was palfed through the mercury : the 

 abforption in that cafe was eleven inches. 



17th. I afterwards examined the effed produced on the fame 

 gas by a piece of charcoal which bad remained five hours in 

 the folar light. Itcaufed an abforption of ten inches and three- 

 lines, which furprized me greatly. 



18th. But to afcertain whether charcoal has any peculiar 

 affinity with carbonic acid gas I tried this gas by placing a 

 piece of cold charcoal in the macliine, and the abforption was 

 nine inches fix lines. 



1 9th. To difcover the efFe6t of carbonic acid gas when mixed A mixture of 

 with atmofpheric air, 1 filled the tube, which is eighteen inches ^^^^ and^^atmof- 

 high, with nine inches of carbonic acid gas, and nine inches pheric air. 

 of the air of my room with the windows open : the charcoal 

 effeded an abforption of twelve inches and three lines. 



On analyfing this experiment, it agrees perfectly with thofe 

 related above, for 



The abforption of the air of my room was 8 inches 1 line. 



■ of the carbonic acid gas 16 6 



Total 21. 7 



The half of this is twelve inches three lines and a half, 

 within half a line of the abforption obtained. 



20th. I afterwards tried the adion of charcoal in hidrogen Hidrogen gas. 

 gas, obtained from iron by fulphuric acid, and the abfoption 

 was three inches and one line : it was accompliftied in five or / 



fix minutes, and flopped at that height ; the effed obferved 

 in my machine did not furprize me, for I had noticed in my 

 firft memoir, that of all the aeriform fluids, hidrogen gas was 

 abforbed the leaft. There is a perfed correfpondence betw^een 

 this experiment, and that which I made in the year 1783, in 

 cryftal tubes of one inch in diameter and twelve in height : the 

 abforption was then two inches and one line, that is to fay, one 

 iixth of the height ; in my new machine, the tube of which is 

 eighteen inches long, the abforption was three inches and one 

 line, which is alfo the fixth of the capacity. 



21ft. On 



