Compound Line-Spectrum of Hydrogen. 339 



called to Randall's paper (Am. Chem. Journ. vol. xix. p. 6$2, 

 1897), my method seemed to have advantages not possessed 

 by his, and I was consequently encouraged to proceed. 



The hydrogen was prepared by Bunsen's method— -the 

 electrolysis of dilute sulphuric acid combining the oxygen 

 with zinc amalgam ; very carefully purified chemicals and 

 apparatus were employed. In order to ascertain the amount 

 of hydrogen with which the palladium was charged, obser- 

 vations were made of the quantity of electricity used for 

 electrolysis. 



The palladium was used in the form of foil, and, as sug- 

 gested by Graham, was first heated to a high temperature, 

 oxygen being passed over it to ensure that any carbonaceous 

 matter should be oxidized : this of course caused some surface- 

 oxidation; but on passing a current of hydrogen over the 

 heated metal and absorbing the moisture, the palladium was 

 left in a suitable condition. The palladium contained in a 

 suitably constructed glass tube was charged with hydrogen 

 by passing a current of gas over the metal previously heated 

 to a very high temperature, and in this way in a short time 

 the tube was freed from the last traces of air ; a stopcock just 

 in advance of the palladium-tube was then closed and the metal 

 gradually cooled in hydrogen, which it thus absorbed to a 

 known amount ; after which connexion with the hydrogen- 

 generating apparatus was cut off by fusing off the connecting 

 tube. 



The palladium-tube was in connexion with a small drying- 

 tube (containing potash which had previously been heated to 

 a high temperature in a silver dish and cooled in a desiccator), 

 and through this with the spectrum-tube and another drying- 

 tube and thence to the pump ; the spectrum-tube was also in 

 connexion with a tube containing potassium permanganate 

 which on heating gave very pure oxygen. 



The spectrum-tube, which was of the ordinary " end-on " 

 description but with the wide tubes longer than usual (to 

 keep the platinum — thrown off by the electrodes — away from 

 the capillary), was constructed conveniently so that the 

 entrance and exit tubes for the gas were near the electrodes. 

 In this way, even at very small differences of pressure, the 

 fresh gas quite displaced that previously in the tube. 



Having first been thoroughly heated with oxygen, the 

 vacuum-tubes were exhausted several times with similar treat- 

 ment until the spectrum of quite pure oxygen was alone seen, 

 this being taken as a criterion of the condition of the tube. A 

 very high vacuum having been obtained, connexion was made 

 with the palladium-tube and a current of hydrogen caused to 



