664 
PROFESSOR W. RAMSAY AND DR. J. SHIELDS ON THE 
it had boiled vigorously for some minutes, and all air had been expelled from tube 
and bulb, the tube was drawn off at the constriction B. The liquid in the barometer- 
tube was then repeatedly boiled so as to remove all traces of air from the walls of the 
tube ; the liquid forms pistons, which are pushed out by its vapour, and effectually expel 
all traces of air or dissolved gas. On cooling the barometer-tube, liquid enters ; when 
a sufficient quantity has entered, the tube is tilted in the direction shown by the 
arrow, to cause mercury to enter; and when all is cold, the constriction C is cut, and 
after the cap has been slipped into position, the tube is inserted into the apparatus. 
It is easy to do this without admitting a trace of air, and the capillary ascent takes 
place, therefore, in presence only of the vapour of the substance. 
The measurement of the capillary rise was effected by means of a very fine 
capillary tube t, enclosed in the wider tube T. This tube, about 6 centims. in length, 
had a minute hole blown in a small bulb at its lower end, and at this point it was 
attached to a shorter and less fragile rod, which served as a support, and on which 
the glass was thickened in several places, so that it maintained a constant position 
in the tube T. Matters were so arranged that the small bulb with the hole in it was 
completely covered by the liquid. The liquid thus gained access to the capillary 
tube, and the heights to which it rose were measured by screwing in the plunger, 
so as to raise the meniscus in the capillary tube t to within a millimetre or two of its 
upper end. By so doing, all the readings were taken at a portion of the capillary 
tube of which the diameter had been measured, and corrections for its probably 
varying bore were thus rendered unnecessary. The diameter of the capillary tube 
was originally measured by cutting off a small cylinder of about half a millimetre in 
length from its upper end, and measuring its internal diameter by a microscope pro¬ 
vided with a micrometer scale, the leno’th of whose divisions Avas determined at the 
same focus by reading against a standard scale. The diameter of the tube used was 
0‘2587 millim. 
In this way a series of heights was obtained for the liquids investigated ; but these 
heights obviously do not represent the true capillary rise; for the liquid in the baro¬ 
meter-tube T ahvays stood at a higher level than if the barometer-tube had been 
of wider bore. 
Corrections .—To correct the read heights so as to make them represent the heights 
in the capillary tube standing in a tube so wide that capillary rise may be neglected, 
the tube T was opened at its upper end, after the measurement had been completed, 
and its lower end was sealed to a tube bent twice at right angles, and connected with 
a tube of about 3 centims. diameter, the axis of which lay parallel to the barometer 
tube. Headings of the height to which the liquid in the tube T (with the capillary 
tube still enclosed) ascended above the level of liquid in the wide-bore tube, where 
capillary rise is too small to be appreciable, were then made Avith the cathetometer at 
the ordinary temperature, 15° to 20° C., the temperature being accurately obseiwed 
at each measurement. KnoAving that the capillary rise is zero at the critical point of 
