FURNACE REACTIONS UNDER HIGH GASEOUS PRESSURES. 427 



transparent cone is forced into the gun-metal fitting after being surrounded with a 

 tli in film of cement, and is held in place hy a metal ring, the shape of the glass 

 tending to make the joint more perfect the higher the pressure. 



The joint betw een the fitting and the aperture in the main forging is made hy the 

 ring a turned on the end of the fitting, which presses tightly against a steel ledge, no 

 packing being required. 



The joint between the fitting and the water jacket is made by means of a gun- 

 metal ring R, which screws on to the fitting itself. 



The two types of window differ only in the relative position of the transparent 

 plug. The design shown at A gives a clearer view of the arc, but for very large 

 currents it is advisable to make use of the fitting B, in which the glass plug is more 

 carefully protected from the source of heat. 



Valves and Gas Connections. 



The types which have already been described* were employed for regulating the 

 flow of the various gases used. 



After the construction of the furnace was completed it was tested to 450 atmos- 

 pheres, and has since been used frequently up to 200 atmospheres gaseous pressure. 



At first it was anticipated that so large a joint as that of the main cover would 

 show some leakage at the higher pressures, the total stress on the bolts retaining the 

 cover amounting under ordinary working conditions to over 100 tons. These fears 

 were, however, not realised, the only precautions necessary being to keep the joint 

 perfectly clean and, of course, to tighten up the nuts evenly all round. Occasionally, 

 as the pressure rose, a slight escape of gas was noticed, but this was stopped without 

 any difficulty by tightening up the corresponding stuffing box or joint. 



In fact, it may be said that throughout the work no difficulty has been experienced 

 in keeping the apparatus gas-tight. 



The furnace is, of course, equally suitable for work in vacuo, and has occasionally 

 been used in this way in connection, for instance, with spectroscopical investigations. 



In the course of the present research the electrical conditions have varied widely, 

 in some cases as much as 1000 amperes, in others 500 volts, having been employed 

 without difficulty. The power used in most experiments was between 10 and 

 15 kilowatts. When it is desired to use high-tension currents (1000-25,000 volts) 

 with this furnace the carbon feeding mechanism of the small apparatus can be used 

 to replace that described above, with which it is interchangeable. 



The weight of the enclosure was, of course, considerable, and to facilitate its 

 manipulation a crane was fixed to the main laboratory wall The crane is regularly 

 employed for the removal of the cover, and serves also to lift the entire furnace and 

 change its position from horizontal to vertical, or vice versd. 



* J. E. PETAVKL, ' Phil. Trans.,' A, vol. 205, p. 369, 1905. 

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