1456 
The eryogene apparatus is completely closed. The vacuum glass 
has a lid # of thin new silver, which is fastened air tight to the 
glass by means of an indiarubber ring, so that when the radium 
tube is in its place, the apparatus can be evacuated, and can be 
filled beforehand with pure, dry gaseous hydrogen (by ZL). A small 
hole in the stopper C,, upon which the radium tube in the alumi- 
nium tube rests, ensures the pressure equilibrium, which establishes 
itself easily during these operations, so that the radium tube is not 
exposed to any danger. 
The liquid hvdrogen is poured into the vessel B through the new 
silver tube 4, and through the india-rubber tube 4,. For this purpose the 
glass stopper is removed which closes the india-rubber tube, after 
the tube with the stopper A, has also been taken away, and the 
india-rubber tube is connected to the syphon A, of the large vacuum 
glass JV, containing the liquid hydrogen that has been previously 
prepared. Before the syphon and the india-rubber tube are connected, 
the apparatus and the vacuum glass are connected to a gasometer 
with pure hydrogen, by the tubes ZL, and L,. When the first 
mentioned connection has been made, the connection of the vacuum 
glass with the gasometer is broken, and the liquid hydrogen is 
poured into the apparatus by means of pressure from a cylinder 
with compressed hydrogen, admitted by the cork m, and controlled 
by the mercury manometer 7. The supply-glass and the gasometer 
are then again connected. The syphon is taken off the inlet tube 
after the connection tube has been warmed, and this latter tube is 
immediately closed by a glass stopper. 
To prevent these manipulations from shaking the apparatus, we 
made the indiarubber tube /,, which is usually as short as possible, 
rather long; but as the great cold makes the india-rubber very 
brittle, and the breaking of it might cause great inconvenience, we 
used only a length of 7 e.m. In this way the shaking remained 
below the limits of stability in the apparatus which we used for 
these experiments. In a larger apparatus, intended for experiments 
that take longer, more than 24 hours, but with which we have 
only been able to make preliminary determinations so far, we were 
able to attain a greater amount of stability, and we were more 
independent of the shaking caused by the manipulations. 
Care must be taken in filling the copper vessel 4, that the liquid 
gas does not overflow, as it might penetrate into the cooling 
chamber, which wouid give rise to irregularities, and might injure 
the radium tube. On the other hand it is necessary to know when 
the liqnid gas has evaporated, otherwise the experiments might be 
