SOLID HYDROGEN. a 



By James Dewar, F. R. S. 



Before proceeding to discuss the immediate subject of this lecture 

 it will be advisable to contrast experimentally some of the properties 

 of hydrogen, nitrogen, and oxygen in the liquid condition. The two 

 vacuum cups (tigs. 1 and 2) are charged half full, respectively, with 

 liquid hydrogen and liquid air. When the cup containing the liquid 

 air is placed in front of the electric lamp the image thrown on the 

 screen reveals the continual overflow of a dense vapor round the outer 







walls of the vessel. The saturated vapor coming from the steady 

 ebullition of liquid air is three times denser than the free air of the 

 room, and the result is it falls through that air just as if it were a 

 dense gas, like carbonic acid or ether vapor. To observe this phenom- 

 enon, the vacuum cup must be shallow; otherwise the vapor gets 

 heated up before reaching the mouth of the vessel, and no difference 

 of density in the air coming off is observed. We will now project the 



'Reprinted from Proceedings of Royal Institution of Great Britain, 1900. 

 at meeting of Royal Institution, April 6, 1900. 



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