on the Electric Arc. 133 



]Fe-G. The arc is blue in colour with a reddish-purple 

 core. The iron boils at its point of contact with the arc, 

 its surface becoming irregular. A black deposit covered 

 the apparatus. A kind or' crater was eaten into the iron 

 as in other metal positives, but was irregular, owino- to the 

 boiling which had taken place. The end of the iron was 

 found to be so hard that a tile would not cut it. 



Al-C. This arc was more unstable than the other metal- 

 carbon arcs. The globe and apparatus were heavily 

 coated with a grey deposit of aluminium. The arc length 

 was difficult to measure owing to the deep crater formed, 

 and the shifting about of the arc. The aluminium wore 

 away rapidly, but did not boil. It looked the same as in 

 air, but no non-conducting formation acted to prevent the 

 re-establishment of the arc. The arc was greyish-blue in 

 colour, with a rather faint purple core. 



C-Cu. This arc appeared brighter than other arcs in 

 hydrogen. The carbon was eaten away very rapidly, but 

 there was no apparent deposit of material in the globe. 

 A grey carbon deposit on the copper terminal tended to 

 make the arc one between carbon electrodes. The arc 

 was more stable than when the current was reversed. It 

 did not travel round on the copper surface and was fairly 

 steady on the carbon except as it ate the latter away. 

 There was no positive crater formed, the end of the carbon 

 being quite irregular. 



C-Fe. There was an intermittent discharge of sparks from 

 all over the end of the carbon, and no steady arc. The 

 discharge could not be maintained for any length of time 

 by the currents used, but would constantly go out. A 

 carbon deposit gradually formed on the iron, and black 

 cobwebs became suspended from the framework and globe. 

 (See fig. I, PL VI.) On continuing to send the current, 

 it became possible to form a steady arc, but it was evident 

 that we now had a carbon-carbon arc. On the carbon 

 electrode there was built up a deposit of feathery branches 

 which extended outward horizontally for f inch all round. 

 The iron was also heavily coated but not with branching 

 deposits. The centre of the carbon was quite deeply 

 cratered, the interior being light grey in colour and pro 

 bably converted into graphite by the heat. 



CJ-A1. This arc was extremely unstable. It would not con- 

 tinue at less than seven amperes. A small lump of 

 carbon deposit appeared immediately on the Al electrode, 

 and the carbon electrode burned away rapidly, the arc 



