MR. MACQUORN RANKINE ON THERMO-DYNAMICS. 
159 
For convenience’ sake, a column is added containing the pressures of steam corre- 
sponding to the temperatures in the table, in pounds per square foot. 
Table of Computed Volumes of 1 lb. avoirdupois of Steam. 
Temperature. 
Volume supposed 
a Perfect Gas. 
Volume computed 
from Latent Heat. 
Difference, 
Ratio of differ- 
ence to lesser 
value of volume. 
Pressure. 
Fahrenheit. Centigrade. 
Deg. 
Deg. 
Cubic feet. 
Cubic feet. 
Cubic feet. 
lb. per square foot. 
— 4 
-20 
15757 
15718 
39 
0-0025 
2-4799 
+ 32 
0 
3390-4 
3377-2 
13-2 
0-0039 
12-431 
68 
+ 20 
936-81 
934-50 
2-31 
0-0025 
48-265 
104 
40 
314-88 
313-56 
1-32 
0-0042 
153-34 
140 
60 
123-65 
122-63 
1-02 
0-0083 
415-33 
176 
80 
55-05 
54-19 
0-86 
0-0158 
988-67 
212 
100 
27-166 
26-478 
0-688 
0-0260 
2116-4 
248 
120 
14-596 
14-076 
0-520 
0-0369 
4149-3 
284 
140 
8+20 
8-004 
0-416 
0-0502 
7557-0 
320 
160 
5-158 
4-838 
0-320 
0-0661 
12931 
356 
180 
3-326 
3-071 
0-255 
0-0830 
20979 
392 
200 
2-241 
2-033 
0-208 
0-1023 
32512 
428 
220 
1-568 
1-396 
0-172 
0-1232 
48425 
464 
240 
1-134 
0-990 
0-144 
0-1455 
69680 
500 
260 
0-843 
0-722 
0-121 
0-1676 
97275 
Col. (1.) 
(2.) 
(3.) 
(4.) 
(5.) 
(6.) 
(?•) 
The fourth column of this table could easily be extended and filled up, so as to 
replace the column of volumes of steam for every fifth Centigrade degree in the table 
previously published ; but it would be unadvisable to do so at present, for the follow- 
ing reasons : — 
Firsts the value of the constant a is still uncertain*. 
Secondly, the results of M. Regnault’s direct experiments, on the density of steam 
and other vapours, may soon be expected to appear. 
Thirdly , it is possible that the values of the latent heat of evaporation of water, as 
deduced from M. Regnault’s experiments, may still have to undergo some correction ; 
because, according to the theoretical definition of the latent heat of evaporation, the 
liquid is supposed to be under the pressure of an atmosphere of its own vapour, which 
atmosphere, as it increases in bulk, performs work of some kind, such as lifting a 
piston ; whereas, in M. Regnault’s experiments, the water is pressed by an atmo- 
sphere of mingled steam and air, whose united pressure is that corresponding to the 
temperature of internal ebullition of the water ; so that the pressure of the steam alone 
on the surface of the water, which regulates the superficial evaporation, may be less 
than the maximum pressure corresponding to the temperature of ebullition ; and this 
steam, moreover, has no mechanical work to perform except to propel itself along 
the passage leading to the calorimeter, and to agitate the water in the latter vessel. 
Under these circumstances, it is possible, though by no means certain, that the latent 
* It is probable that y. maybe found to be inappreciably small; in which case, the numbers in column (4.) 
will have to be diminished to an extent varying from T -l-gth t0 teto^ their amount. 
