554 



Professor Sir James Dewar 



[Jan. 



'-)'! 



shape is slipped over the platinum tnbe, which it loosely fits, and to 

 which it is luted at the plain open end nearest the sealed joint by a 

 short plug of asbestos wool ti^rhtly packed when wet. The purifica- 

 tion of the gas entering the quartz tube, and thus passing through 

 the annular space round the platinum tube, is provided for by a plain 

 U-bend G, which is cooled in a vessel of liquid air or solid carl)onic 

 acid. A second bulbed U-tube containing a little mercury or sul- 

 phuric acid is sealed in near the open end of the quartz cover tube, 

 and this acts as a seal and bubbler H for controlling the gas rate. 

 The tubes are conveniently heated by a Meker burner F. 



Plate 7 shows the observed increase in the pressure when the 

 platinum tube is heated directly in the flame in three different 



Plate 7. — Growth of Pressures in Platinum Tube Heated by 

 Meker Gas Burner. 



positions. The rate of growth of the pressure and the limiting 

 pressure reached are seen to be dependent on the region of the flame 

 to which the platinum tube is adjusted ; when near the bottom, 

 where the amount of unburnt hydrogen is greatest, a rapid rise is 

 shown and the equilibrium pressure obtained is high, both values 

 becoming less as the platinum tube is brought higher in the flame. 

 Finally, at the tip of the flame where combustion is complete, reversal 

 can be demonstrated, and the manometer again falls in the manner 

 shown in the diagram ; for the hydrogen will diffuse out as vvell 

 as in, the direction depending on whether the region of lowest 

 pressure is outside or inside. The position of equilibrium of the 



