73 EXPERIMENTS on EVAPORATION. 



N'. X. 



Experimenis on Evaporation^ by C. Wistar, M. D. 



Read Feb. T N an Eflay publlfhed in the laft Volunfie of the 

 5, 1796- X Tranfadions of the Society, I defcribcd a 

 fpecies of evaporation which was excited by fufpending 

 ice, at the mehing point, in air reduced to the tempe- 

 rature of o of Fahrenheit's fcale ; and confidered it as the 

 effedt of a genei^al law of nature, in confequence of which 

 an inelaftic vapour, (which commonly is vifible,) arifes 

 from water, and from wet fubftances, whenever they are 

 warmer than the atmofphere which lurrounds them. 



From fa<fts ftated in the fame paper it was inferred, that 

 this inelaftic vapour does not depend upon any pofitive 

 quantity or degree of fenfible heat in the evaporating 

 body, but upon a relative degree, exceeding that of the 

 atmofphere to which it is expofed ; and that it is pro- 

 duced by the paflage of heat from the moift body into 

 the contiguous air. — If this theory be true, it follows 

 that a flow diftillation may be performed, with the com- 

 mon apparatus, by applying cold to the receiver or re- 

 frigeratory, without increafmg the heat of the retort or 

 fubftance to be dirtilled, as there will be a continual 

 paflage of heat from the body to be evaporated or diftilled, 

 into the air of the receiver. 



Although, for the reafons there given, I had no doubt 

 ef the truth of the do£lrine advanced in my former paper, 

 1 was defirous of fubmitting it to the teft of this experi- 

 ment, becaufe it has been fuggefted that the vapour 

 which appeared to arife from ice, might have arifen from 

 the mixture of different portions of air of different tem- 

 peratures ; 



