280 Messrs. Gee and Holden on the Change of 



Testing for Palladium Salts. 

 A supply of the liquid having been obtained by a similar 

 process to the above, a solution of potassium iodide was added 

 to it, but no evidence of the presence of palladium was obtained. 



Streaks obtained in Phosphoric Acid. 

 Similar streaks were obtained in solutions of pure ortho- 

 phosphoric acid by adopting exactly the same procedure as 

 with sulphuric acid. 



Streaks obtained in Caustic-Soda Solution. 

 In this case also streaks were obtained descending from one 

 of the electrodes, but the conditions necessary for their appear- 

 ance are very different to those in the case of sulphuric and 

 phosphoric acids. No previous reversal of the current is neces- 

 sary, and the streaks descend from the kathode immediately 

 the current is passed. The gas (hydrogen) formed at the 

 kathode is at first absorbed, and the streaks are seen to descend 

 as long as the absorption takes place; but, when gas begins 

 to be evolved briskly, the streaks disappear. By very careful 

 observation it is seen that the liquid of which the streaks 

 are composed is still formed, but is carried up in the current 

 of gas to the surface of the electrolyte, from which it re- 

 bounds, giving the electrolyte round the kathode the peculiar 

 wavy appearance which accompanies the incomplete mixing 

 of two liquids of different densities, such as two strengths 

 of the same solution. 



Explanation of the Caustic-Soda Streaks. 

 This experiment led us to infer that the streaks in the 

 caustic-soda solution are composed of concentrated alkali, 

 which is known to be formed at the kathode, and that the 

 absence of evolution of gas from that electrode is a necessary 

 condition for their appearance and steady downward flow. 

 The part played by the palladium in the formation of the 

 streaks is, according to this theory, that of absorbing the 

 hydrogen, which otherwise, in escaping from the electrode, 

 would carry the concentrated solution along with it to the 

 surface and thus prevent the formation of the streaks. 



Explanation of Streaks in general. 

 Since in acids concentration occurs at the anode, the descend- 

 ing streaks, if seen at all, should be seen at that electrode. 

 But taking sulphuric acid as an instance, oxygen is given off 

 at the anode, and the palladium cannot retain it sufficiently 



