132 Mr. W. L. Upsrm : Observations 



Cu-Al. The aluminium was the upper cooled electrode. 

 This arc is more persistent than with the electrodes 

 reversed in polarity. It is easily started, but is very un- 

 settled in character, emitting constantly a hissing and 

 spitting sound, and travelling about, over the surface of 

 the electrodes, tending to lengthen out. But it does not 

 go out as easily as the arc between the same terminals 

 when the current is reversed. The flame is principally 

 green from the copper. Sometimes the whole crater will 

 be green with merely a thin aureole of blue. The alumi- 

 nium electrode was covered with a golden-brown deposit 

 from the copper, and its end was hard and pitted. 



Al-Cu. The arc was blue in colour from the aluminium 

 terminal, and green from the copper terminal, about 

 equally divided. It was very unstable, and acted much 

 like the Al-Al arc, being impeded in starting by the 

 aluminium oxide. The arc would continually lengthen 

 out until it ruptured itielf . 



Fe-Al. The aluminium was above and cooled. The arc 

 is as to be expected, blue with a yellow aureole. It 

 shows the characteristic aluminium tendency to glide 

 about and play around the edges of the electrodes. It is 

 less steady than the copper arcs. The poles presented much 

 the same appearance as those of the Fe-Cu arc. The Al 

 electrode was embedded with iron to a considerable depth. 



.Al-Fe. The aluminium was eaten into very slightly. The 

 iron appeared as in the case of the Cu-Fe arc. 



Arcs in Hydrogen. 



C-C. The arc was pale blue in colour, with a faint purple 

 core. Its length was difficult to measure on account of 

 heavy carbon deposits. The carbons became shaped so 

 that their ends formed parallel spherical surfaces, the 

 positive being concave. Around the edge of the negative 

 was built up a branching deposit of carbon, extending 

 outward about a quarter of an inch. Compare arcs of 

 carbon and iron. 



Cu-C. The arc was small and pale, consisting of a central 

 core of reddish-purple colour, enveloped by a region of 

 green light. It persistently travelled around, fin ding no 

 point of permanent attachment, and wearing a broad 

 crater in the positive and shaping the negative to fit the 

 crater. The end of the carbon became very hard, with a 

 deposit of copper, while around the outside edge was soft 

 carbon which easily fell away. The surrounding globe 

 was blackened by a fine carbon deposit. 



