33.2 Mr. T. Tate's Experimental Researches on the 



was unusually dry, the temperature being 53° ; so that the vapo- 

 rization, considering the elevation of the temperature of the water 

 above that of the surrounding air, might be regarded as taking 

 place in dry air. 



Table of results of Experiments giving the rate of the cooling 

 effect of Evaporation. 



Tempera- 

 ture, in 

 degrees 

 Fahr. 



Wet canister. 



Dry canister. 



Rate of 

 cooling 

 due to eva- 

 poration, 

 v. 



Corre- 

 sponding 

 tension of 

 vapour, 

 P- 



Value of v 



by formula 



_px L 



"~ 2330 ' 



Intervals 



of time, 



in minutes, 



for 10°. 



j Rate of 



icooling per 



| minute, in 



degrees 



Fahr. 



Intervals 



of time, 



in minutes, 



for 10°. 



Rate of 



cooling 



per minute, 



in degree 



Fahr. 



180 



175 

 170 

 165 

 160 

 155 

 150 

 145 

 140 

 135 

 130 

 125 

 120 

 115 

 110 



1 







1*45 

 1-75 

 2*20: 



275* 

 3*5*0 



4-50 

 570 



6*90 



i'-sfi" 



4-54 

 3-63 

 2-85' 

 2-22 

 i V 7*5* 

 







8*33 



9 17 



10-5*6 



1200 

 13-7*6 



1570 

 1800* 



1-20 



1-09 

 •95 

 •83 



,-73 

 •63 

 •55 



570 

 4-62 

 3-59 

 2-80 

 212 

 1-59 

 1-20 



13-635 



10-820 



8-512 



6-633 



5116 



3-907 



2-949 



5-62 

 450 

 3-56 

 2-79 

 217 

 1-67 

 1-26 



The values of L are calculated from Regnault's formula for 

 the latent heat of steam, viz. L = 1082- -695 T; thus for the 

 temperature 175°, we find L = 1082- -695 x 175 = 960-375; 

 and so on for other temperatures. The near coincidence of the 

 results m the sixth and eighth columns shows that the cooling 

 effect of the evaporation of water nearly varies as the product 

 of the tension of the vapour and the latent heat of that vapour. 

 This result was also verified in the following manner. 



Experiment II. Two tin canisters were made of the same 

 form and capacity; but the one was closed at the top, as in the 

 foregoing experiments, whilst the other was open at the top. 

 They were filled with the same quantity of hot water and exposed 

 to the atmosphere, and the times of cooling, &c, were noted as 

 before. In this case, presuming the radiation from the surface of 

 the water to be the same as the radiation from the corresponding 

 surface of the tin, the difference between the corresponding rates 

 of cooling obviously gives us the rate of cooling due to evapora- 

 tion alone. In this experiment the observations were made at 

 intervals of 5° Centigrade. 



