ЗЕСТ. II.] 
PROPERTIES OF STEAM. 
51 
tain not only its own 188°, but also the 188° lost by each of the other four parts; 
that is to say, it must contain 188° x 5, or about 940° of heat. 
76. The experiments of Dr. Black are not greatly different from the result 
obtained by Schmidt, for the latter found the heat of steam to be 5*33 times the 
heat which is required to boil water of the temperature 32°, the barometer being 
at 29*84 inches. 1 This is the best mode of expressing the heat, for there is reason 
to believe that the specific heat of water is not the same for every rise of tempe 
rature. But to reduce it to the usual measure in degrees, there are 180° between 
the boiling and freezing point, hence 180 x 5*33=959°*4 for the additional heat of 
steam. 
77. Mr. Southern, and Mr. W. Creighton in 1803, made some experiments 
by condensing steam with a considerable degree of care; the steam being gene 
rated at different temperatures and pressures. The pressure, temperature, heat of 
formation, and bulk of the steam, from a cubic inch of water, are shown in the 
following table : 
Pressure in inches 
of mercury. 
Temperature. 
Heat required to 
form the steam. 
Bulk of steam 
from one cubic 
inch of water 
at 60°. 
Bulk calculated 
from the first ex 
periment. 
40 
229° 
1157° 
208 
1208 
80 
270 
1244 
588 
635 
120 
295 
1256 
404 
427 
If from the whole heat we deduct the difference of temperature, we have 1157°, 
1203°, and 1190°; whence it appears that the heat to form steam is nearly a 
constant quantity when the temperature is the same, being independent of the 
density. 
Therefore the most convenient mode of expressing the quantity of heat is that 
adopted by Mr. Southern, which consists in ascertaining the constant quantity of 
heat required to be added to the actual temperature of the steam to give the whole 
heat necessary to form it. This quantity is 
1157—229=928°; 1244-270=974°; and 1256-295=961°; and the mean 
is 954°. 
In another set of experiments, made under the same pressures and tempera 
tures, the quantities of heat required in addition to the temperature were 942°, 942° 
and 950°, 2 the mean being nearly 945°, and the mean of both sets 949°. In this 
set of experiments an allowance was made for the heat communicated to the 
vessel; in the former set none was made. 
1 Nicholson’s Philosophical Journal, vol. v. p. 208. octavo series. 
2 Robison’s Meehan. Phil. vol. ii. p. 160—166.