HEAT OF EVAPORATION OF WATER. 
Taste XVIII. 



I. Il. iil. II 
(millim. of Hg). ee (dynespersq.centim.).) p (millim. of Hg). 
| \¢ 
| 
° | | 
0 330 | 44.0 1-1 4-569 
20 1073 | 14308 17-363 
40 2:936 | 39150 54°865 
66 6:922 | 92301 148-89 
80 14°388 191850 30487 
100 26981 | 359800 760° 





325 
The numbers in Column III. are obtained by assuming g = 980°94 and density of 
mercury = 13°596. 
The resulting values of s’ (specific volume) and d (density, air = 1) are given in the 
following table :— 









TABLE XIX. 
| 1. II. | Te IV. 
Temperature. 8. | Specific volume of air. d. 
| 
° | 
0 207970 | 128600 6184 
20 58430 36318 6215 
40 19581 12278 “6270 
60 7644 4814 6298 
80 3395°6 2141 6305 
100 16769 1056°2 6299 
The specific volume of air was calculated by the formula 
1 (273:0 + 0) _ 760 a, FBO O 
0012935 273-0 Nine fio 
The value of dp/dT at low temperatures is not known with sufficient precision to 
enable us to attach any weight to the resulting values of d. For example, if we take 
dp/dT = 331 millim. at 0° instead of °330 millim., we get d = ‘6204 in place of 
6184. At temperatures above 20° or 30°, not only is the value of dp/dT known with 
greater certainty, but the effect of any small error is diminished. 
A comparison of the ‘“‘ Theoretical Density ” (-6206) with the numbers in Column IV. 
of the last table, indicates that aqueous vapour at low pressures approximates in 
density to that of a perfect gas, but that, at higher pressures, its density exceeds that 
of a perfect gas. 
Above a pressure of about 140 millims., it appears to attain a practically constant 
density about 1015 times that of the “ theoretical ” one. 
