134 Mr. W. L. Upson : Observations 



always remaining attached to the carbon deposit on the 

 aluminium. There appears to have been no increase in 

 the white aluminium deposit on the globe after the arc 

 had been changed from Al-C to C-Al. This may have 

 been because the arc was not attached directly to the 

 aluminium surface. 



Cu-Cu. With clean terminals no arc could be maintained 

 in hydrogen with 110 volts supply and 15 amperes at 

 contact, not even the shortest. On drawing the electrodes 

 apart, a shower of sparks, or arcs, appeared, but imme- 

 diately went out. Previously an arc was obtained, using 

 a copper rod on which some carbon had been left from a 

 former experiment. The arc remained until the carbon 

 was exhausted. 



Fe-Fe. No permanent arc could be maintained. The 

 spark shower lasted only a little longer than that with 

 copper electrodes, but no length at all appreciable could 

 be obtained between the electrodes while the sparking 

 lasted. The sparks were numerous and gave the same 

 hissing sound that usually accompanies a spark discharge 

 in a vessel. The terminals were reversed, but with the 

 same result. The sparks were pale blue in colour. The 

 lower iron rod presented the same appearance as in the 

 iron-copper arc below. The upper electrode was covered 

 with a black deposit, but at one spot was a bare globule 

 of metal where the contact had been made. 



Al-Al. This gave better results than Fe-Fe, or than Al 

 in combination with either Cu or Fe. The arc was 

 reddish-purple or magenta coloured, and travelled about 

 continuously, finding no point of permanent attachment. 

 The metal was eaten into somewhat as in other arcs of 

 Al in H. Attempts were made to steady the arc by 

 shaping the lower electrode. The worst effect was 

 obtained when this was pointed, for the arc stretched 

 out to such lengths as to continually rupture itself. The 

 current was also far more variable, in this case, than 

 when the ends of the electrodes were flat and parallel. 

 The colour of the arc was found to vary with its length, 

 being reddish for short arcs and more bluish as the arc- 

 length increased. There was considerable dull grey 

 deposit from this arc, and the upper electrode seemed to 

 be considerably built up with aluminium carried over 

 from the lower. 



Cu-Fe. This was very unstable. It consisted of a shower 

 of sparks which was continually going out. There was. 

 some black deposit on the globe. 



