( 230 ) 
described at greater length elsewhere (Thesis for the doctorate, 
Chapt. VID. At that period however these measurements could not 
be very accurate, in consequence of the work in the eryogenie 
laboratory being legally prohibited on account of its alleged dangers, 
so that we could not adequately use liquid gases for reaching low 
temperatures. Hence I resorted to a mixture of solid carbon-dioxide 
and aleohol; but then the temperature remained constant only for 
a short time, and the value given is not quite accurate. 
The difficulty mentioned being removed, I have taken this work 
up again, and am now able to communicate some figures, obtained 
by means of a bath of boiling nitrous oxide, i.e. at a temperature 
of about — 90° C. 
2. The liguid-bath. Two forms of vessel for the liquid gas 
have been used. 
The first consisted only of a very narrow vacuum-glass, outer 
diameter 33 m.m., inner diameter 21 m.m., height about 35 c.m. 
This was filled to two thirds of its height with liquid nitrous oxide 
by means of the spiral packed in solid carbon-dioxide, described in 
Comm. N°. 51, § 41). It was then mounted between the poles of 
an electromagnet. The experimental apparatus could be placed in the 
vacuum-glass before filling this, so that after filling only the necessary 
leads had to be connected; usually however it was lowered into the 
vacuum-glass after this had been placed between the poles, and 
was then quite ready for the experiment. 
A single filling, in which about 0.4 kgm. of nitrous oxide in all 
was taken from the cylinder, was sufficient to cover the apparatus 
for more than two hours. A draw-back of the use of vacuum-glasses 
is however the large space between the poles, which is required 
even with this narrow glass, and prohibits the use of comparatively 
intense fields. 
In order to meet this difficulty a second form without a vacuum 
wall 2) was constructed, drawn in fig. 1. The vessel for the liquid 
in the strict sense of the word consists of a cylindrical wooden 
receptacle a, in the bottom of which a vessel made of compressed 
paper with oval section and wooden bottom is glued. Externally 
1) Verslag der Verg. Kon, Akad. v. Wet. Amsterdam, 30 September ’99, p. 135. 
Comm. Phys. Lab. Leiden NO. 51. 
*) In the same way in the ethylene boiling flask (Comm. NO, 14, Versl. Dec. °94) 
the condensed gas is only sufficiently protected against heat by air-spaces and wool 
wrapping. 
