( 169 ) 



the cock jSF, PI. I, we connect 



eu. 



Fi?. 3 



with the tube A^o and the India 

 rubber tube J,, instead of the 

 silvered tlasks of PL II and 

 PI. Ill, a transparent vacuum 

 cylinder fig. 3a, closed by an 

 India rubber ring with a new- 

 silver cap witii inlet tube. After 

 the cock is opened the India 

 rubber outflow tube c/j covers 

 with rime and becomes as hard 

 as glass; soon the first drops in 

 spheroidal state are seen splash- 

 ing on the bottom of the glass and 

 the lively liquid fills the glass. If, 

 as shown by fig. 36, a glass cover 

 is placed on the top, the glass 

 may be left standing in the 

 open air without the air con- 

 densing into it, which would hasten the evaporation. In the same 

 manner I have sometimes filled non-silvered vacuum flasks holding 

 1 liter, where the liquid hydrogen boils vividly just as in the glass 

 mentioned before. The evaporation is of course much less and the 

 rising of the bubbles stops when the vacuum glass or the vacuum 

 flask is placed in liquid air. 



To demonstrate the pouring of hydrogen 

 from one open vessel into the other, I use 

 a glass, cap round which a collar of thin 

 India rubber sheet is bound (comp. the 

 accompanying fig. 4). The flask from which 

 and the glass into which we want to pour, 

 the latter after being filled with liquid air 

 and quickly turned down and up again 

 (if this is not done quickly a blue deposit 

 of HjO from the air will come in), are placed 

 ' Fig. 4 under the cap, which fills with hydrogen and 



hence remains transparent, then with the India rubber round the neck 

 of the bottle and round the glass we take hold of the two, each in 

 one hand. Tlirough the cap we can observe the pouring. The escaping 

 hydrogen rises in the air as clouds. 



In order to keep the half filled glass clear it is covered, under 

 the pouring off" cap, with a glass cap, and so it can bo taken 

 away from the pouring off cap. 



