GASES ABSORBED BY CHARCOAL. 2^1 



After two hours the charcoal abforbed one inch two lines. 

 After three hours, one inch eight lines. 

 After five hours, two inches. 

 After feven hours, three inches nearly. 

 It is difficult to obtain very precife refults, becaufe the heat The light unltee 

 of the fun is greatly varied, according to the wind ; but in ^^ j '^ ^^' 

 this cafe it is light as light which unites with the charcoal, for 

 in very cold days when the thermometer in the (hade was at — 

 6^, I flill obtained an abforption *. 



9th. Being defirous of afcertaining whether this abforbent 

 property belonged to charcoal exclufively, I tried fevera! other 

 bodies, which there was reafon to believe contained a great 

 deal of the matter of fire. 



10th. I took a fmall cylinder of loaf fugar, cold; it did not Experiments •n 

 produce the fmalleft apforption. ^°*^ ^^^"* 



A fimilar piece, which I had heated in a matrafs with boil- 

 ing water, gave an abforption of between two and three lines. 

 A piece of fugar which had been expofed to the fun for two 

 hours alfogave an abforption of between two and three lines. 



11th. I then proceeded to the examination of fulphur and on fulphur, 

 fealing wax. 



A cylinder of fulphur of the fame weight gave no abforp^ 

 tion when cold. 



A iimilar cylinder, which had been expofed four hours to the 

 light of the fun, gave an abforption of about three lines. 



A piece of cold fealing wax did not give the leaft abforption, and on fealing- 

 and a fimilar piece which had been two hours in the fun, gave^^** 

 an abforption of about two lines. 



12th, All thefe fmall abforptions which were obferved as 

 well in the fugar as in the fulphur and fealing wax, were only 

 owing to the flight heat of thefe bodies, which produces a di- 

 latation in the air of the cavity, and a difplacing of that por^ 

 tion of the air which is filled by the folid body ; for a piece of 

 pumice ftone, of cork, or of any other body, produces the 



* It would be intereftlng to examine the abforptions which might 

 be produced by different pieces of charcoal which had been in the 

 light of the fun tranfniltted through coloured glafTes, or by making 

 the different coloured rays fall on the charcoal by means of aprifm, 

 and to obferve whether the piece expofed to the red ray would abforb 

 more or lefs than that which had received the violet ray, and fo of 

 the others, 



fame 



