( 34 ) 
At the lowest temperature that we can expect!) the mercury 
stands at the lower end of the reservoir o and at the upper end of 
the reservoir »; at the highest temperature?) the mercury must 
remain in the lower end of the reservoir n. It may be easily seen 
on the plate how the regulator controls the flame. The narrow glass 
tube ¢ is drawn out atits lower end until the bore is less than 2 m. m., 
then it is ground flat and after this ground at a slant, so that we 
obtain a lengthened opening. This end of the tube ¢ is placed at 
the narrow opening of the tube p; a slight increase of temperature 
is sufficient to diminish the supply of gas perceptibly but gradually. 
In order to fill the regulator the tube q was closed at its higher 
end by means of an india-rubber stopper and carefully exhausted 
through the side-tube ending in a point which was broken off under 
xylene. The india-rubber stopper is removed, the spiral is immersed 
in a bath of over 25° CO. and mercury is poured into it. The 
xylene bubbles through the mercury and is removed; then the bath 
is slowly cooled to the desired temperature, in my case 20° C, 
taking care that always sufficient mercury remains; by means of a 
narrow glass tube as siphon, small quantities of mercury may be 
removed for adjustment to different temperatures. 
This regulator would also be insufficient, if the regulating flame 
had to be used to heat all the water streaming through as in the 
case of VAN ELDIK; its only purpose however is to serve as a regu- 
lating flame, while a constant flame v must warm the water to a 
little below the temperature desired. In order to avoid heating of the 
mixing bath from the side it is protected by an asbestos plate z. 
§ 4. Use and results. If we want to set the apparatus working, 
the clip w is kept closed, the stirring apparatus are put in motion 
and we begin to slowly heat the heating bath. Then boiling water 
must slowly be poured through the open window O into the mixing 
bath, until the desired temperature is reached. When this tempera- 
ture is almost reached in the heating bath, the dip w is opened. 
First the constant flame is regulated so, that it can heat the water 
to almost the desired temperature and then it is somewhat diminished: 
this difference must be supplied by the regulating flame, which 
even while burning at its highest must be much smaller than the 
constant flame and may never be extinguished. 
1) In the Phys. Lab. at Leiden rooms, when necessary, can be heated night and day ; 
the lowest temperature may therefore be kept higher than 0° C. 
2) Supposed to be 25° C. the isotherm is determined at 20° C, 
