60 THE ROYAL SOCIETY OF CANADA 
(c). The motor-pump supplied worked perfectly. The pumping- 
connections were attached to the second stop-cock on the top of the 
gasometer, and the electrical connection made with the switch-board. 
It was not necessary to use it continuously, as it was found possible 
to obtain the most uniform pressure by maintaining the gasometer 
working with a maximum raise of the cylinder equal to about two feet. 
If raised much farther the inner cylinder came into contact with the 
outside one through not being quite evenly balanced, and altered 
the regular flow of air. The air-current was regulated by pinch- 
cocks on the rubber-tubing connections. 
(d). The drying-bottles contained C.P. H.SO,, and arrangements 
for bubbling the air, or air and emanation, through it. 
(e). The radium solution used contained 1-57 x 10 grams of 
radium. It was fitted with a two-hole rubber stopper through which 
passed two lengths of glass tubing, one passing almost to the bottom 
of the solution so that the air could be bubbled through it, while the 
other extended only to the bottom of the rubber stopper. The stopper 
was sealed down with vacuum wax and wired. 
(f). The microscope was newly-cleaned and showed a good 
clear scale. It was focussed on the gold-leaf at the beginning of the 
experiment, and then fixed in position with paraffin. 
(g). The chronometer used was a new one and regulated. It 
was further checked for half-minute intervals with the second-hand 
of the clock in the Elementary Laboratory in the Physics Building, 
and showed absolute agreement for half-a-dozen consecutive instances. 
(h). The thermometer used read to about 130° C. 
(2). The thermostat consisted of a large glass beaker two-thirds 
full of water. The temperature was maintained constant by means of 
a thermo-regulator. This consisted of a large glass tube 3 mms. in 
diameter in the stem, and a large cylindrical bulb at the end about 
3-8 cms. diameter. The greater part of the bulb was filled with toluol, 
and the remaining portion as well as the greater part of the stem, 
with mercury. Toluol is used in the bulb because its coefficient of 
“expansion is much greater than mercury, and makes it more sensitive. 
A separate part, consisting of a vertical tube and two side branches, 
is fitted into the stem of the thermo-regulator with a rubber stopper. 
The quantity of mercury in the stem must be so adjusted that the 
lower part of this separable piece just touches the surface of the 
mercury at the temperature of the experiment. The working-principle 
of the thermo-regulator then follows: 
Connect up the gas for heating the flask with the separable part 
of the thermo-regulator. It divides itself so that one portion passes 
down the vertical tube and out to the bunsen through the side-tube 
