ON THE THERMAL PROPERTIES OF ALCOHOL. 
25 
A similar correction was made for the surface of the alcohol, no apparent change 
taking place until its temperature was raised to within a few degrees of its critical 
point. At those temperatures it was found that the error was inappreciable. 
The experimental tube was heated by the vapours of pure liquids, boiling under 
pressures which could be varied at will. The vapour-pressures of these liquids have 
been accurately determined, temperature being measured with a mercury thermo¬ 
meter. Several measurements were carried out with an air-thermometer, and the 
necessary corrections were applied to reduce the readings of the mercurial thermometers 
used to those of an air-thermometer. The details of this investigation have been 
given in the Trans. Chem. Soc., 1886, p. 37 ; the results which are there published 
constitute a guarantee of the accuracy of the determination of temperature. We can 
state with confidence that at the highest temperature employed (246°) the absolute 
error does not amount to two or three-tenths of a degree; and the temperature can 
be altered with certainty through 0 - 05° by alteration of the pressure under which the 
liquid is boiling. This is, we believe, the only method by which a long tube can be 
uniformly heated; and by which the temperature can be easily and quickly altered. 
All the temperatures given are, therefore, those of an air-thermometer. 
5. It is unnecessary to give details as regards reading, calibration, &c., for all our 
results. But as it may help to explain our method of procedure, one instance shall be 
given, and the method may be held to apply to all the other results. 
The temperature on an air-thermometer at which aniline boils at an observed 
pressure of 703*2 mms., the temperature of the gauge being 14° (equivalent to 701'5 
mms. at 0°), is 181'4°. At this temperature, the following readings were made :— 
Beading in experimental tube of upper surface of mercury, 210. Beading of upper 
surface of liquid, 139*7. Corresponding volumes corrected for meniscus: volume of 
liquid plus gas =0‘65974 cc. ; volume of gas =0'39591 cc. Add correction for expan¬ 
sion of glass ; for higher volume, 0*00309 ; for lower volume, 0*00186. Corrected 
volumes = (l) 0*66283 ; (2) 0'39777 cc. Volume of liquid = 0*26506 cc.; volume of 
gas = 0*39777 cc. The volume was subsequently reduced, until only a minute bubble 
of vapour was left uncondensed. It was thus made certain that the liquid, as such, 
was not being compressed. The corrected volume was then found to be 0*28706 cc. 
The weight of the liquid in the tube was 0'17083 grm.; this latter number was found 
from several readings of the volume at known low temperatures, and the known 
specific gravity of alcohol at those temperatures. 
The specific gravity of alcohol under pressure corresponding to that of its own 
vapour at 181*4°=0*17083/0*28706 = 0*5951. From this number is deduced the 
weight of the liquid (vol.) 0*26506 X (sp. gr.) 0*5951 = 0*15774 grm. The weight of 
the vapour=total weight—weight of liquid=0*17083— 0‘15774=0 , 01309 grm. 
The weight of 1 cc. of vapour therefore equals its weight divided by its volume 
= 0*01309 grm./0*39777 cc. = 0*0329 grm. 
Vapour density:—Weight of 1 cc. H at 181*4°and 15,163 mms. pressure =0*001074. 
Hence 0*0329/0*001074 = 30*65, 
