426 



MESSRS. R. S. HUTTON AND J. E. PETAVEL ON ELECTRIC 



Carbon Holders. 



These are of two different patterns, according to the size of the electrode used. 



Carbons of 30 millims. diameter or less are held by clamps similar to those used 

 with the smaller furnace, as shown at T in fig. 6 (p. 429). 



For larger carbons the limited space available prohibits the use of such an arrange- 

 ment, which in any case would hardly provide a sufficiently good contact for heavy 

 currents (500 to 1000 amperes). 



The larger carbons are therefore electro-coppered at their ends, and soldered into 

 cup-shaped holders, as shown at H (fig. 3). The lip of the cup is fitted with a ring 

 of refractory insulating material, U, which nearly fits the bore of the tube K, and 

 thus protects the stuffing box from flame and dust. 



Fig. 4. Windows. 



A and B. Gun-metal fittings carrying the glass windows W. 

 F. Steel wall of furnace enclosure, 

 a. Gas-tight ring joint. 



R. Ring making water-tight joint between the fitting and the water jacket K. 

 The design A is used when working with arcs of small intensity, and B for larger currents. 



Windows. 



Although unnecessary for the purely chemical work, it was of considerable 

 importance to be able to observe, project, or photograph the arc itself or its spectrum 

 under conditions of high pressure.* By providing two openings (B and C, fig. 2) 

 diametrically opposite, absorption spectra could be observed during the operation of 

 the arc. 



The forms of construction are shown in fig. 4. The window itself consists of a glass 

 or quartz cone (W) f inch thick and inch diameter at its smaller end. This 



* " Preliminary Note on the Effect of Pressure upon Arc Spectra," J. E. PETAVEL and R. S. HUTTON, 

 1 Phil. Mag.,' Nov., 1903, vol. 6, pp. 569-577. 



