100 Mr. W. Crookes. [June 11, 



If, for the negative electrode, instead of a pure metal such as 

 cadmium or silver, an alloy was used, the different components might 

 be shot off to different distances, and in this way make an electrical 

 separation a sort of fractional distillation. A negative terminal 

 was formed of clean brass, and submitted to the electrical discharge 

 in vacuo ; the deposit obtained was of the colour of brass throughout, 

 and on treating the deposit chemically I could detect no separation 

 of its component metals, copper and zinc. 



[A remarkable alloy of gold and aluminium, of a rich purple colour, 

 has been kindly sent me by Professor Roberts- Austen. Gold being 

 very volatile in the vacuum tube, and aluminium almost fixed, this 

 alloy was likely to give different results from those yielded by brass, 

 where both constituents fly off with almost equal readiness. The 

 AuAl alloy had been cast in a clay tube in the form of a rod 2 cm. 

 long and about 2 mm. in diameter. It was sealed in a vacuum tube 

 as the negative pole, an aluminium pole being at the other side. Part 

 of the alloy, where it joined the platinum wire passing through the 

 glass, was closely surrounded with a narrow glass tube ; a clean glass 

 plate was supported about 3 mm. from the rod of alloy. After gcfod 

 exhaustion the induction current was passed, the alloy being kept 

 negative. Volatilisation was very slight, but at the end of half an 

 hour a faint purple deposit was seen both on the glass plate and on 

 the walls of the tube. On removing the rod from the apparatus, it 

 was seen that the portion which had been covered by the small glass 

 tube retained its original purple appearance, while the part that had 

 been exposed to electrical action had changed to the dull white colour 

 of aluminium. Examined under the microscope, the whitened surface 

 of the Austen alloy was seen to be pitted irregularly, with no trace 

 of crystalline appearance. This experiment shows that from an alloy 

 of gold and aluminium the gold is the first to volatilise under elec- 

 trical influence, the aluminium being left behind. The purple colour 

 of the deposit on glass is probably due to finely divided metallic gold. 

 The first deposit from a negative pole of pure gold is pink; this 

 changes to purple as the thickness increases. The purple then turns 

 to green, which gets darker and darker until the metallic lustre of 

 polished gold appears. June 10.] 



Returning to the analogy of liquid evaporation, if we take several 

 liquids of different boiling points, put them under the same pressure, 

 and apply the same amount of heat to each, the quantity passing 



to imagine that when the extra activity is produced by electricity the emission of 

 red light should also accompany the separation of molecules from the mass. In 

 comparison with electricity heat is a wasteful agent for promoting volatilisation, 

 as the whole mass must be raised to the requisite temperature to produce a surface 

 action merely ; whereas the action of electrification does not appear to penetrate 

 much below the surface. 



