192 New experimental Researches 
On this subject I am not acquainted with any preceding in- 
quiries, though a question of such interest has probably not 
escaped examination. 
In this research 1 employed a very simple apparatus ; and with 
proper management, I believe it capable of giving the absolute 
quantities of latent heat in different vapours, as exactly as more 
refined and complicated mechanisms. At any rate, it will afford 
comparative results with great precision. 
It consisted of a glass retort of very small dimensions, with a 
short neck inserted into a globular receiver of very thin glass, 
and about three inches in diameter. The globe was surrounded 
with a certain quantity of water at a known temperature, con- 
tained in a glass basin. 200 grains of the liquid, whose vapour 
was to be examined, were introduced into the retort, and rapidly 
distilled into the globe by the heat of an Argand lamp. The tem- 
perature of the air was 45°, that of the water in the basin from 
42° to 43°, and the rise of t temperature, cecasioned by the con- 
densation of the vapour, never exceeded that of the atmosphere 
by four degrees. By these means, as the communication of heat 
is very slow between bodies which differ little in temperature, I 
found, that the air could exercise no perceptible influence on the 
water in the basin during the experiment, which was always com- 
pleted in five or six minutes. A thermometer of great delicacy 
was continually moved through the water; and its indications 
were read off, by the aid of a lens, to small fractions of a degree. 
In all the early experiments of Dr. Black on the latent heat of 
common steam, the neglect of the above precautions introduced 
material errors into the estimate. Hence that distinguished phi- 
losopher found the Jatent heat of steam to be no more than 800° 
or 810°. Mr. Watt afterwards determined it more nearly from 
900° to 950°; and Lavoisier and La Place have made it 1000°. 
It is evident that whenever the water, into which the latent 
heat is evolved by condensation of the vapour, becomes much- 
hotter than the surrounding air, it will be impossible to ascertain 
how much of the caloric is dissipated ; and consequently, the true 
quantity contained in the vapour must remain uncertain. 
The sources of error in operating with the calorimeter of La- 
voisier and La Place were first pointed out by Mr. Wedgwood, | 
and have been since commented on by Dr, Thomson, and other 
good systematists. It is said to be difficult to obtain precisely 
uniform quantities of liquefied ice in the repetition of the same 
experiments, with that celebrated apparatus. 
From the smallness of the retort in my mode of proceeding, 
the shortness of the neck, and its thorough insertion into the 
globe, we prevent condensation by the air in transitu; while the 
surface of the globe and the mass of water being great, relative. 
to 
