1897.] Newly Prepared Gases. 371 



temperature of the cell being 36°. In both cases a dense cloud 

 was observed above the water in H 2 . 



In order to test the efficiency of the apparatus, for removing 

 the acid vapour, and at the same time to show that newly pre- 

 pared hydrogen does not form a visible cloud unless it has a 

 considerable charge, the gas evolved from the carbon electrode 

 was led into ff 1 . It was found that the electrometer was giving 

 only 3 divisions per minute and no cloud could be seen over the 

 surface of the water in H 2 , although the temperature of the cell, 

 and current through it, were the same, as when 37 divisions 

 per minute were obtained by using a platinum electrode. In 

 weighing experiments were performed in order to find the ratio 

 of the weight of the cloud to the charge, but it could easily be 

 seen that the cloud was less dense than that which would be 

 formed in similarly electrified gas evolved from a sulphuric acid 

 electrolyte. 



In addition to the above experiments, the effect of Rontgen 

 rays in discharging the gas has been examined. It is hoped that 

 the results of this investigation, and the experiments on con- 

 ductivity alluded to in section 13, will be ready for publication in 

 the near future. 



In conclusion I desire to express my thanks to Professor 

 Thomson for the valuable assistance his suggestions have afforded. 



(3) On a chemical effect produced by the impact of kathode 

 rays. By Professor J. J. Thomson and Mr S. Skinner. 



Aluminium is rapidly evaporated from the kathode by an 

 electric discharge in a highly exhausted vacuum tube in which 

 air has been replaced by mercury vapour. The metal is con- 

 densed over the walls of the tube in the form of a bright mirror. 

 An iron kathode gives a similar mirror in a mercury vapour 

 discharge tube. When the aluminium coating is dissolved off 

 the wall of the bulb by hydrochloric acid a gelatinous membrane 

 remains which gives the reactions of silica, and the escaping 

 hydrogen has an unpleasant odour from the small quantity of 

 silicon hydride which it contains. The iron mirror dissolves 

 completely in hydrochloric acid. From these observations it 

 appears that aluminium driven off from a kathode by an electric 

 discharge acts on the glass, forming a silicide, which on solution 

 in hydrochloric acid yields aluminium chloride, gelatinous silica 

 and some silicon hydride. 



When potassium vapour is used in the place of mercury the 

 glass opposite the aluminium kathode is roughened. In parts 

 sheltered by screens from the discharge the glass is not attacked. 



VOL. IX. PT. VII. 30 



