( 135 ) 
back from the conduit Y,, from introducing dust into the apparatus. 
For the tube Z, through which in the experiments of Dr. HASENOEHRL 
the gas escaped which evaporated from the electric measuring-con- 
denser, a simpler dust-box Z, (filled only with cotton wool between 
gauze) was sufficient, as this has not to transmit so much gas at 
once. It has already been pointed out above, that the arrangement 
of this cryostat offers a great advantage as concerns easy mounting 
and dismounting. This is especially due to the use of flanges with 
packing for all the air tight joints that have to be made and tem- 
porarily broken in working with the apparatus. 
The copper wall with flanges soldered to it will of course occasion 
no leakage, and can be tested previously by means of a temporary bottom 
soldered into it and temporary closing plates on the flanges. When 
we are quite certain everything is tight, the caoutchoue cap, which 
is to close the bottom, is spread over with rubber-solution, and by 
means of bands W, onee for all united with the ease. In the same 
manner the cap Az is fitted onto the cover and the arts going. through 
the holes. When all this has been done carefully, the joints are tested 
by immersing the case with bottom and cover, closed with temporary 
plates on the flanges, in a tub filled with water, and protecting the 
caoutchoue caps from without against inflation; then admitting air 
into the case under a little excess of pressure (0,2 atm.), and seeing 
whether any air bubbles escape. These fittings which demand much eare 
are permanent, so that if they are found in this manner to be 
secure, they will not generally require any more attention. In the 
same way we may also carefully cement once for all the thick plate 
glasses ovj, g> and the flanges of the observing and illuminating-tubes 
in the caoutchouc-tubes «ej #9, and test the joints by means of tem - 
porary flanges before fastening them to the apparatus. 
In commencing to use the cryostat we need only serew the case 
on to the cover Ny and the observing-tubes onto the side-flanges, 
and secure an exact fit of the packing between the flanges, a thing 
which can always easily be attained. This is the case also if we 
wish to lift the boiling-glass with the cover for a moment out of 
the case, or if we must renew the P.O; in the drying-dishes in 
the observing- and illuminating-tubes. 
The cryostat rests with N, on a wooden ring supported by three 
legs and is packed up in wool. 
It was described above how in the experiments of Dr. HASENOEHRL 
the measuring-apparatus was mounted in the boiling-glass. We may 
add here only that, as explained by him in Comm. No. 52, the 
beaker B, was filled with liquid oxygen from the ethylene-boiling- 
10 
Proceedings Royal Acad. Amsterdam. Vol. Il. 
