2^ 



On charcoal 

 heated without 

 the contaft of 

 lire. 



and cxpofed to 

 the folar light. 



GASES ABSORBED BY CHARCOAL. 



2d. The tube of my glafs was eighteen inches long, from the 

 bottom of the key to the furface of the mercury, the level of 

 which is indicated by the moveable fcale. The diameter of 

 the tube is three lines and a half: it contains one ounce and 

 feven drams — five grains of water, or a volume of atmof- 

 pheric air of four grains and a half at a temperature of -{-10^, 



3d. Being defirous of throwing a light upon the property 

 polfefled by charcoal of abforbing a part of the atmofpheric 

 air, as well as of feveral gafes, by means of my new inftru- 

 ment, I made a great number of experiments, which I Ihall 

 now defcribe. 



4th. Charcoal, when cold, has the property of abforbing 

 fome fmall portions of atmofpheric air, and this abforption, al- 

 though very flow, is not complete in lefs than twenty-four 

 hours. 



5th. Wifliing to try whether charcoal to which heat had 

 been communicated without direft expofure to fire, would (how. 

 any abforbent power, I placed a piece in a fmall matrafs, 

 which I immerfed in boiling water for an hour; having after- 

 wards put the charcoal into the machine, I obtained an ab- 

 forption of about three inches. 



6th. I boiled oil, in which I left the matrafs for an hour ; 

 an experiment with this charcoal gave an abforption of three 

 inches two lines. 



7th A fmall matrafs containing a piece of charcoal was im- 

 merfed for an hour in boiling alkaline lixivium : it gave an 

 abforption of three inches three lines nearly. 



Thefe three experiments ftiow that heat communicated to 

 charcoal, even without the conta6l of fire, gives it the pro- 

 perty of abforbing a larger portion of air. 



8th. The preceding experiments induced me to examine 

 whether the light of the fun would communicate the fame 

 property to charcoal, I therefore expofed different pieces to 

 this light, in a white porcelain bowl, and the abforptions were 

 proportionate to the times which the pieces were expofed to 

 the light of the fun *. 



* At the inftant of putting a piece of charcoal into the machine, 

 1 placed another which had been expofed with the reft to the fun for 

 three hours, on the bulb of a thermometer j it only raifed one de- 

 gree and a half of Reaumur's fcale : the heat therefore was not 

 very confiderable, . 



After 



