on the Electric Arc. 131 



Ou-Cu. A steady green arc could be drawn out to 0*2 in. 

 with 2'5 amperes. The terminals were very little affected, 

 being somewhat oxidized. A shallow crater was formed 

 in the negative, and a small hard bubble of oxide on the 

 positive. 



Fe-Fe. This arc is very steady at low currents and small 

 arc-lengths. It is blue-coloured, with a yellow aureole. 

 As the arc-length and current are increased, yellow 

 fumes are given off in considerable quantity, and a 

 deposit of yellow-brown powder, no doubt iron oxide, 

 covers the apparatus. The terminals, also, begin to boil 

 and the arc becomes less steady. When the bubbles 

 make their appearance the arc begins to hiss, and there 

 appears to be an increase in the amount of power con- 

 sumed in the arc. The boiling iron disturbs the arc, 

 making it difficult to get accurate readings. There is 

 also a hissing when the arc changes its point of attach- 

 ment on the positive electrode. This is accompanied, as 

 in the carbon-hissing arc, by a fall in voltage, but is quite 

 distinct from the hiss which accompanies the boiling 

 iron. 



Al-Al. This arc was found to be very unstable. The 

 terminals became quickly oxidized where the arc is 

 formed, causing the latter to travel around continually, 

 seeking unoxidized portions, and tending to lengthen out 

 and run up the sides of the terminals, finally going out. 

 The arc is a clear blue colour with a thin yellow aureole. 

 On each pole is a bright spot where the arc enters. A 

 small grey deposit was formed on the framework. 



•Cu-Fe. The arc is bluish, with a yellow aureole. No 

 copper-green is visible. The iron bubbles form a con- 

 ducting oxide (magnetite), which, when cool, may be 

 knocked off the end of the terminal. Also a bubble, or 

 deposit of iron is left on the copper if the arc has been 

 burned for a little time. There is also some brown iron- 

 oxide deposit on the electrodes. 



Fe-Cu. The copper was the upper cooled electrode. The 

 arc showed a greenish colour, getting stronger at the 

 copper electrode. Toward the iron it was blue. On 

 knocking off the cap of oxide which covered the end of 

 the iron, a heavy deposit of pure copper was found buried 

 in the iron underneath. Quite a deep crater was burnt 

 into the copper, while in the reverse experiment prac- 

 tically no effect was to be observed on it. The whole 

 copper terminal was covered with a brown sooty deposit. 

 R2 



