xviii Historical Sketch of the Physical Sciences, 1818. 
We see from this table, that the specific heat of each of these 
eight solids (unless platinum be an exception) increases with the 
temperature. Whether this increase of capacity be owing to the 
increase of dilatibility (the cause assigned by Dalton) cannot be 
considered as decided; but the experiments of Dulong and 
Petit, so far as they go, tally very well with such an opinion. 
Platinum increases the least in its dilatibility by heat ; it under- 
goes also the smallest augmentation of its specific heat. The 
order of the increase of the dilatibility of the other metals tried 
is, mercury, copper, iron. Now these metals follow the same 
order in the increase of their specific heat. But it would be 
requisite to make a set of experiments on purpose on a greater 
number of bodies, and at higher temperatures, in order to obtain 
a satisfactory solution of this intricate question. 
4. Latent Heat of Vapours.—Iit is universally known that Dr. 
Black first pointed out that when liquids are converted into 
vapours, a considerable quantity of heat becomes /atent ; and 
there could be no doubt, from a variety of obvious phenomena, 
that every vapour has a latent heat peculiar to itself. But 
though nearly 60 years have elapsed since the original discovery 
of this curious and important fact, I am not aware of any expe- 
riments to determine the latent heats of different vapours, except 
those by Mr. Watt to determine the latent heat of steam. These 
experiments have been lately printed; but as they are not yet, 
{ believe, published, I do not consider myself at liberty to 
give an account of them here. Count Rumford also published a 
set of experiments, by which he ascertained the latent heat of 
steam and of alcoholic vapour. These latent heats are as 
follows : 
NECA «casein sae eg nse n SUSU O, 
Vapour of alcohol, between 477°0° and 500° 
In this deficiency of experiments, those who are interested in the 
subject lie under considerable obligations to Dr. Ure for a set of 
experiments which he has given in his paper on heat printed in the 
Phil. Trans. for 1818. His mode of proceeding was to distil a 
given weight of the liquid, the specific heat of whose vapour was 
to be determined into a receiver surrounded by a known weight 
of water, and to estimate the specific heat of the vapour by the 
increase of temperature which the water sustained. As no allow- 
ance was made for the heat dissipated during the experiment, it 
is obvious that the latent heats given by Dr. Ure are below the 
truth. Perhaps they will approach pretty nearly the true num- 
bers if we increase them by about th. The following table 
. . J i) 
exhibits the results of Dr. Ure’s experiments. 
SL eee ae Seige se thieves GOL O00 
Vapour of alcohol ....-.++e+00++ 442000 
