1880.] 



Note on Electrolytic Experiments. 



171 



On first plunging the wire beneath the surface nothing is observed ; 

 almost immediately, however, it becomes intensely illuminated all over 

 the surface. The light seems to emanate from an immense number of 

 points which look like lit up gems. This appears to be due to the 

 formation of oxide of aluminium, which offers a great resistance to 

 the passage of the current and consequently becomes intensely heated, 

 and is pierced or disintegrated at certain points, and this supposition 

 seems to be confirmed by the absence of any incandescence of the 

 wire when hydrochloric acid, caustic potash, or any other medium 

 which dissolves the oxide as soon as formed, is used. If another 

 aluminium wire is substituted for the platinum plate, then either the 

 one or the other becomes illuminated according to the extent of surface 

 of metal immersed, but they are generally not illuminated at the same 

 time, the largest surface always remaining dull ; gases are now freely 

 given off, being chiefly hydrogen. 



The luminosity of the aluminium wire becomes very much diminished 

 after a short time, as the wire becomes almost completely covered with 

 -a uniform layer of the white oxide, and is gradually eaten away. The 

 luminosity can again be produced by cleaning the poles. The same 

 effects took place when dilute hydrochloric acid, or saturated chloride 

 of sodium was substituted for the dilute sulphuric acid. After the 

 -current had passed for some time gas was given off at both poles. 



The light evolved from the surface of the poles below the 

 •surface of the electrolyte was intensely white, and on spectroscopic 

 examination, proved to be the characteristic channeled spectrum of 

 oxide of aluminium, first described by Thalen. The characteristic 

 metallic lines between the two H lines were faint. 



On bringing a piece of thin foil aluminium as one pole near the surface 

 of the acid it is immediately fused, globules of the melted metal flying 

 about in all directions ; the aluminium wire is also fused after a short 

 time, and falls through the liquid in white hot globules. 



Magnesium wire at one pole, the other being the platinum plate as 

 •before, gave an intense green colour below the surface, a spectroscopic 

 examination showing the combined spectrum of the metal and oxide. 



It burnt on the surface of the liquid in the same manner as the 

 .aluminium, showers of melted metal being thrown off ; the action when 

 a saturated solution of chloride of sodium was employed was, if any- 

 thing, more intense. Similar actions took place with other metals, 

 such as copper and zinc. 



A solution of chloride of sodium was rapidly decomposed, abundance 

 of chlorine being set free, when a platinum wire was used as one pole, 

 ■the larger platinum plate being used for the other. A solution of 

 iodide of potassium behaved in the same way, but was decomposed at 

 a very much slower rate when both the poles were of large surface. A 

 saturated solution of sulphate of copper deposited hardly a trace of 



