328 Review of Renwick 
into vapor at the temperature of 212° expands nearly 1700 times; 
but at the temperature of 419°, it expands but 37 times. Dr. 
Thomson, in his recent work on Heat and Electricity, adds, “that it 
is probable that at a temperature not much higher than 500°, the 
steam of water would not much exceed double the bulk of the water 
from which it was generated. ‘The expansive force of such steam 
- would be truly formidable. It would, when it issued into the atmos- 
phere, suddenly. expand almost 650 times.. We do not know at what 
temperature water would become vapor without any increase of vol- 
ume. But it would then support a column of mercury 3243 feet in 
height, and exert a force of 19.459 lbs. upon every square inch of 
the vessel containing it.”* . : ) 
4, The absolute quantity of heat is always the same in the same 
weight of steam, whatever may be the temperature of that steam. 
When the vapor is formed at a low temperature, nearly all the heat 
that enters it is in the latent state; but as we heat it to a higher de- 
gree, its proportion of sensible heat is constantly augmented, and of 
latent heat diminished in the same ratio, so that the sum of the two 
isthe same constant quantity.f ; 
_ “If (says Dr. Thomson) we could apply such a pressure to water, 
that we could heat it till its sensible heat arose to 1212°, it is obvious 
that it would be converted into steam having the specific gravity, and 
consequently the volume of the original water. The. latent heat of 
* Outline of the Sciences of Heat and Electricity, p. 222. = h 
_ t As some of our readers may not be familiar with the precise’ signification set 
with this subject, we will briefly explain them. ‘Latent heat is that which cH 
into a body while changing its state from solid to liquid or from liquid to annem 
which portion of heat is not sensible to the thermometer, but disappears oF becomes 
1 Annan & 
latent as water does uick lime. Thus, when water is converted int 
steam in the common process of ebullition, a quantity of heat enters into the water 
to convert it into steam, which if applied to water would be sufficient to raise it nest 
ly 1000 degrees, but which does not raise the temperature of either the water or the 
unit. Th , 
steam is said to have a specific heat of 1.7778, because if we take equal weights a 
air and steam at the same temperature, it can be proved that the actual x 
heat which these two bodies contain are in that ratio to each other. The term 
-_ heat contained, while the other denotes the ratio of the po 
taining these respective quantities, which ratios are evidently the same 1» 
7 
