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24.

fired, the clamp was again placed in operation until the system had been taken from the 3-inch pipe and the smoked glass removed.

The circuit which carried the electric current to ignite the charge consisted of the insulated wire, [[underlined]] W [[/underlined]], Fig. 15, which pass ^[[ed]] through a tapered plug of shellacked hard fibre, in the cap, [[underlined]] C [[/underlined]], thence through a glass tube to the yoke [[underlined]] Y [[/underlined]], to which it was fastened. Below the yoke it was wrapped with insulating tape, except at the lower end where it was shaped to hold the ^[[0.]] 24 mm. steel wire, attached to the fine copper wire from the wadding. From the chamber the current passed up the rods [[underlined]] R [[/underlined]], [[underlined]] R [[/underlined]] and out of the cap, around which was wrapped a heavy bare copper wire, [[underlined]] V [[/underlined]], which together with [[underlined]] W [[/underlined]], constituted the terminals of the circuit. It should be mentioned, in passing, that a small amount of black powder, [[underlined]] B [[/underlined]], Fig. 6(a), placed over the platinum fuse-wire on the wadding, was found necessary as a primer in order to ignite dense smokeless powders in vacuo. 

In order to make the joint ^[[,]] between the cap and the pipe ^[[,]] air tight during a determination, the following device was adopted. The outside of the cap, [[underlined]] C [[/underlined]] ], and also a lock nut, were both turned down to the same diameter. The lock nut was made fast to the pipe. These were then painted on the outside with melted wax consisting of equal parts bee's wax and resin with a little Venice turpentine.

When a determination was to be made, the cap was screwed into position, a wide rubber band was slipped over the junction between cap and lock nut, and the outside of this rubber band was heated with an alcohol blast torch. The result was a joint, for all practical purposes, absolutely air tight, which could, nevertheless, be dismounted at once after pulling off the rubber band.