586 



Professor Sir James Deivar 



[Jan. 19, 



is almost fiiil of air. The rate of evaporation from the three tubes 

 may be judged by the relative volumes of air in E, F, G, the 

 proportion found being about 2 : 10 : 3. While the manufacture of 

 vacuum vessels is restricted to glass, probably no increased efficiency 

 will be obtained by the use of powders as isolating agents, but if such 

 fiasks were made of fused silica the method might have considerable 

 advantages. Silica flasks would Avithstand very high temperatures, 

 which would, however, render the use of silver as a reflecting sur- 

 face an impossibility ; although nickel might be used. If such a 

 flask could be made quite impervious to gases, which is extremely 

 doubtful, it would be especially suital)le for the isolation of red hot 

 bodies. 



Liquid Air and Hydrogen Drops. 



In a Friday Evening Discourse on " Liquid Hydrogen Calori- 

 metry," * the mode of manipulation of liquid gases for calori metrical 



y) 



Fig. 7. 



A shows the simple construction which can be used with the 

 instrument made in quartz ; if glass is used as in B, then a spiral 

 has to be sealed in the exit tube, to take up the contraction caused 

 by cooling to low temperatures. 



experiments was discussed. One fact which renders this simple 

 method of calorimetry more difficult than it appears is the mobility 



• Proc. Roy. Inst., xvii. p. 581. 



