SECT. 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. l 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 180x5-33=959 0> 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 : 



If from the whole heat we deduct the difference of temperature, we have 1 157, 

 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 Mechan. Phil. vol. ii. p. 160166. 



