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VII. On a Method of Freezing at a distance. By William Hyde 

 Wollaston, M. D. Sec. R. S. 



Read December 17, 1812. 



1 HAT a fluid, from which a portion is evaporated, becomes 

 colder in consequence of the heat absorbed by that part which 

 assumes the gaseous state : that fluids rise in the state of 

 vapour at a lower temperature when the pressure of the at- 

 mosphere is removed, and consequently may be cooled to a 

 lower degree by evaporation in vacuo than in the open air, are 

 facts too well known to need confirmation before the Members 

 of this Society by any new experiments. 



Nevertheless, a new mode of applying the most established 

 principles may deserve to be recorded, if it assist the illustra- 

 tion of them, and be instructive from the novelty of the view 

 in which it exhibits a certain class of phenomena ; although 

 no immediate use be at present proposed, to which it can be 

 applied with advantage. 



If an attempt were made to freeze water by evaporation, 

 without other means than the vacuum of an air-pump, the 

 pump must be of the best construction, and though the quan- 

 tity of water be small, the receiver must be of large dimen- 

 sions, otherwise its capacity would set too confined a limit to 

 the quantity of vapour that will rise, and consequently to the 

 degree of cold produced. 



Supposing the commonly received estimates to be correct. 



