886 Dr. Ure’s new experimental researches 
In this research I 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 pre- 
cision. 
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 tem- 
perature, contained 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 temperature of the air was 45 0 , that of 
the water in the basin from 42 0 to 43 0 , and the rise of tem- 
perature, occasioned by the condensation of the vapour, 
never exceeded that of the atmosphere by 4 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 
completed in 5 or 6 minutes. A thermometer of great deli- 
cacy was continually moved through the water; and its 
indications were read off, by the aid of a lens, to small frac- 
tions 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 dis- 
tinguished philosopher found the latent heat of steam to be 
no more than 8oo° or 8io°. Mr. Watt afterwards deter- 
