Laws of Evaporation and Absorption. 



333 



Table of results of Experiments giving the rates of the cooling 

 effect of Evaporation. 





Canister open at top. 



Canister closed at top. 









Tempera- 



. 







Rate of 



Corre- 



Value of v 



ture, in 



Intervals R ate of 





Rate of 



cooling due 



sponding 



by formula 



degrees 



oftin7e L C00lin »P er 





cooling 



to evapora- 



tension of 



_pxh 



Cent. 



minutes, 

 for 5° C. 



minute, in 

 degree 

 Cent. 



minutes, 

 for 5° C. 



per minute, 



in degree 



Cent. 



tion, v. 



vapour, 

 P- 



14000" 



o 



65 





















62-5 





•926 





•469 



•457 



6 533 



•458 



60 



5-40 





1066 











57*5 





757 





•384 



•373 



5-208 



•367 



55 



6-60 





13 00 











52-5 





•612 





•316 



•296 



4-094 



•291 



50 



8-16 





15-83 











475 





•460 





•230 



•230 



3191 



•228 



45 



10 85 





19-50 











42-5 



! -379 





•213 



•166 



2450 



•176 



40 



1317 | 



23-41 











The values of L are taken in degrees Fahrenheit, as in the 

 foregoing Table of results. The near coincidence of the results 

 in the sixth and eighth columns confirms the law above enun- 

 ciated. 



The following series of experiments not only verify this law, 

 but also determine the maximum depression of temperature 

 produced by the evaporation of water in dry air of a given tem- 

 perature. 



Experiment III. A large wide-mouthed bottle, containing a 

 portion of strong sulphuric acid, had its mouth closed by a per- 

 forated cork having the stem of a delicate thermometer passing 

 through it. The thermometer was graduated into tenths of a 

 degree Centigrade ; and having an elongated bulb, a calico cap 

 could be readily slipped on or taken off the bulb as required. By 

 agitating the sulphuric acid, the air in the bottle was dried or 

 deprived of all watery vapour. The temperature of the air being 

 first ascertained by the naked bulb of the thermometer, the bulb 

 of the thermometer with its calico cap moistened with water 

 slightly above the atmospheric temperature was placed in the 

 bottle, and the rate of cooling, &c, were carefully noted. The 

 rate of cooling, given in the second column of the following 

 Table of results, is the number of degrees, or parts of a degree, 

 which the thermometer fell per minute below the atmospheric 

 temperature. 



