EFFECT OF PRESSURE UPON ARC SPECTRA. 
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window in the side of the cylinder, made of glass ground into the shape of a truncated 
cone, and so fitted into its seat in the cylinder that an increase of pressure tends to 
make the joint tighter. The whole cylinder is surrounded by a water-jacket through 
which water circulates and carries off the heat generated by the arc. Details of the 
design are described elsewhere, # and fig. 8 merely indicates diagrammatically the 
essential features of the apparatus. The stuffing-boxes in the covers perform the 
function of insulating the electrodes from the sides of the cylinder, besides that of 
permitting a vertical motion of the feed-rods without escape of gas. 
The maintenance of the highest pressures for long periods without appreciable 
leakage testifies to the excellence of Mr. Petavel’ s design. The writer here desires 
to express his indebtedness to Mr. Petavel for the use of the pressure cylinder and 
connections, and for valuable advice upon their management. 
For the production of pressure within the cylinder the gas holder H, fig. 8, which 
was filled with air at a pressure of 120 atmospheres, was placed in communication 
with the pressure cylinder through the valve V, which could also afford a means for 
the escape of the gas from the pressure cylinder A to the outlet pipe. Pressure 
gauges indicated the pressures in the gas holder and in the cylinder. 
* Hutton and Petavel, ‘ Electric Furnace Reactions under High Gas Pressures,’ read Royal Society, 
March 7, 1907. 
