EXPERIMENTS on EVAPORATION. 7^^ 



peratures j whereas by dlftilling or evaporating in a luted 

 retort and receiver, there can be no mixture of warm and 

 cold air ; and by ufing a fubltance which is not contained 

 in the atmofphere, we ihall avoid all lufpicion that the 

 vapour which arifes from it, may have originated from 

 the air in the veflels. 



With thefe views 1 poured an ounce and half of vitrio- 

 lic asther into a retort and luted it to a receiver with a long 

 neck, which was placed in a mixture of fait and fnow, 

 while the retort was furrounded by air of the temperature 

 of 50° of Fahrenheit. The frigorific mixture, from the 

 impurity of the fait, was feldom below 10°, fo that the 

 difference, between the aether in the retort and the air 

 in the receiver, did not exceed 40°. 



When the apparatus had been thirty hours in this 

 Situation the frigorific mixture was removed, and one 

 third of the aether was found diftilled into the receiver. 



I believe no caufe can be afligned for this diftillation but 

 the pafTage of heat through the aether into the cold air 

 of the receiver i and to be certain that the application 

 of cold to the receiver really produced it^ I prepared a 

 fimilar diftilling apparatus, in the fame manner precifely, 

 and placed the retort in contadt with that of the other ap- 

 paratus, while the receiver, inffead of being chilled by 

 the cold mixture, flood in air of the fame temperature 

 with the retorts, viz. 50° ; but no diftillation took place 

 during thirty hours. 



To vary the experiment, I placed feme camphor in 

 another apparatus prepared as above, and fixed the receiver 

 in the frigorific mixture, while the retort flood in air of 

 the temperature of 50", at the expiration of thirty hour* 

 fome of the camphor was found fublimed, and the fub- 

 limate had thofe arborefcent appearances which ufually 

 attend it when produced by heat. 



Memoir 



