452 



Lord Rayleigli. On 



[Feb. 18, 



air, the pressure in the generator is always nearly atmospheric. Some 

 trouble has been caused by leakage between the platinum electrodes 

 and the glass. In the later experiments to be here recorded these 

 joints were drowned with mercury. On leaving the generator the 

 hydrogen traverses a red-hot tube of hard glass charged with copper,* 

 then a flask containing a strong solution of potash, and afterwards a 

 second similar hot tube. The additional tube was introduced with 

 the idea that the action of the hot copper in promoting the union 

 of the hydrogen with its oxygen contamination might be more com- 

 plete after removal of the greater part of the oxygen, whether in the 

 combined or in the uncombined state. From this point onward the 

 gas was nearly dry. In the earlier experiments the junctions of the 

 hard furnace tubes with the soft glass of the remainder of the ap- 

 paratus were effected by fusion. One of these joints remained in use, 

 but the others were replaced by india-rubber connexions drowned in 

 mercury. It is believed that no leakage occurred at these joints; 

 but as an additional security a tap was provided between the 

 generator and the furnace, and was kept closed whenever there was 

 no forward current of hydrogen. In this way the liquid in the 

 generator would be protected from any possible infiltration of 

 nitrogen. Any that might find its way into the furnace tubes could 

 easily be removed before the commencement of a filling. 



Almost immediately upon leaving the furnace tubes the gas arrives 



* The copper must be free from sulphur ; otherwise the contamination with 

 sulphuretted hydrogen is somewhat persistent. 



