200 
and saturated steam, or steam raised in a boiler over water, 
is found to take up nearly double quantity of water to 
form steam of double density or pressure; but the latent 
heat in steam is directly as the quantity of water converted 
into steam, whilst the sensible heat in it is only as above 
stated, viz. : — 
from 212° at 14‘71bs., to 240 q ' at 251bs., increase 28° 
„ 240° at 251bs., to 281° at 501bs., „ 41° 
„ 281° at 501bs., to 827i° at lOOlbs., „ 46J° 
The decreasing latent heat in steam is found to be nearly as 
the increasing sensible heat, or, in other words, the absolute 
heat is nearly in proportion to the water changing its form 
of a liquid to an elastic vapour. 
By the increase of sensible heat, all liquids and solids are 
gradually expanded, and by the abstraction of such heat, 
they are contracted in bulk ; but the degrees of expansion 
and contraction are different in bodies, as shown in the 
mercurial and spirit thermometers, the Wedgwood pyro- 
meters, and the different metallic rods used for compensation 
balances and pendulums. In all such cases, the gradual 
changes of bulk by the gain and loss of sensible heat, the 
law governing the changes is quite distinct from that which 
rules in the cases of sudden changes of water and other 
liquids into steam and again back into the liquid form, and 
by which changes of constituent forms, absorption and 
liberation of heat takes place, to the extent before shown, 
beyond what is indicated by the thermometer. 
It thus appears quite clear that the entering of heat 
latent in steam is a consequence of water being converted 
from its liquid state to that of aqueous vapour, and the 
reappearance of the same heat, in a sensible state, when the 
