[ 133 ] 
VIII. On the Surface-condensation of Steam. ByJ. P. Joule, LL.D.., F.E.S., 
President of the Literary and Philosoiyhical Society of Manchester, &c. 
Eeceived October 10, — Eead December 13, 1860. 
The laws which regulate the transmission of heat through thin plates of metal under 
various circumstances, although of extensive practical application, and although their 
elucidation would necessarily involve scientific conclusions of great interest, have hitherto 
received little of the attention of natural philosophers. Two great divisions of the 
inquiiy are, first, the communication of heat from the products of combustion to a 
boiler ; and second, the application of cold to a vessel employed for the condensation 
of steam. With a ^iew to supply some information on the latter subject I have, with 
the assistance of a grant from the Royal Society, undertaken the present research. 
The adjoining sketch (p. 134) will explain my apparatus. B is a steam-boiler into the 
side of which a pipe P furnished with a stopcock T is screwed. Jointed to this by a 
caoutchouc tubulure t is the condensing pipe s, connected at the lower end to a short 
pipe y, which in turn is connected with the copper receiver R, closed at the bottom by a 
screw-nut n furnished uith a washer of india-rubber. The refrigerating water is trans- 
mitted through the channel E D C, consisting of a pipe 1-|- inch in diameter, and the 
concentric space between the steam-condensing pipe and an exterior pipe of larger 
diameter. The refrigerating water on flowing away is collected in V, the vessel in which 
it is afterwards weighed. In order to avoid the necessity of applying a large correction 
to the temperature of this water, it is, when its quantity is not very great, received in 
the first instance by the small can U, in which a thermometer is plunged. A branch 
pipe p, screwed into the main pipe, is connected to the barometer tube h in order to 
measure the degree of vacuum. 
The pipe P enters the boiler at 8 inches above the surface of the water. Separate 
experiments showed that no water came up to this height by “ priming.” On the other 
hand, the arrangement of the boiler, the flue of which is entirely below the level of the 
water, prevented the steam being surcharged with heat to any notable extent. 
By careful experiments I found that a thermometer of which the bulb was held six 
inches above the water of the boiler, indicated exactly the same temperature whether 
the boiling was carried on very slowly or very rapidly. But when the bulb was im- 
mersed 3 inches below the surface, the temperature with slow boiling was 0°‘532 higher 
than that of the steam, Avhich difference was further increased to 0°’538 by rapid boiling, 
This would lead to the belief that the steam must have been a little overcharged with 
heat by passing through superheated water ; but as there was a trifling cooling effect by 
the influence of the atmosphere on the pipe P, the steam passing through the stopcock 
might be safely considered as neither superheated nor mixed with water. 
MDCCCLXI. u 
