Force of Steam. 1 
produce double the effect) I have not yet 
made any direct experiment to determine.* 
In stating the latent heat of steam to be 
uniformly the same at all temperatures, it must 
be understood, with reference to the quantity 
of water converted from the fluid to the gase- 
ous state, and not to the quantity of space 
occupied by the steam, as the actual quantity 
of heat increases progressively with the den- 
sity. In order to obtain steam of any given 
density, a specific temperature corresponding 
with that density is also necessary ; aud with- 
out that temperature the steam cannot exist. 
If it be required to produce steam equal to 
two atmospheres, that can only be done by 
raising it from water at the temperature of 
252°, or thereabouts; and if an additional 
weight or pressure is put upon the steam so 
raised, or if the temperature is lowered a few 
degrees, and the pressure of two atmospheres 
continues, in either case it will be immediately 
condensed into water again, although the 
temperature still continues several degrees 
above the common boiling point. The fol- 
lowing experiment will shew this:—Take a 
barometer tube, hermetically sealed at one 
* This seems to have been proved by Gay Lussac. 
An. de Chimie, Vol. 43. 1802. or Nicholson’s Journal, 
Vol. 3. p. 267. 
B 2 
