A bond wire, to get best results, should be homogeneous, made of a single piece of metal, or if made of several pieces, all the pieces should be welded, or at least, soldered together. They should be of sufficient length to insure flexibility without disturbing the connection if the rails should move relatively to each other, and the whole circumferential surface of the plug end, or its equivalent, when possible, should be in the closest possible direct contact with the rail, that is, the bond plug should make connection with the rail as nearly as possible—homogeneous. Welding would be the ideal connection but it is not always practicable.
The reason for the above is obvious: that there should be no room left between the bond and rail for rust to form. It follows then that a bond held in position by an independent plug which renders it necessary for the current to pass from the bond to the intermediate plug and from that plug to the rail, is not the best form of bond, for the reason that it presents a double surface on which rust may form.
Figures 11 and 12 show Robinson's bond wires and strips of 1872, Fig. 12 showing the bond soldered to the rail.
In 1876, 7 and 8 he used on various roads in the vicinity of Boston, the bond shown in Fig. 11. In 1876 he used on the Boston and Providence road the bond shown in Figs. 11, 13 and 14.
In the form shown in Fig. 13, holes are bored through the upper ends of the plugs, which were slightly tapering. The wire was forced through these holes, and the wire and plugs were then soldered together with hard solder. The plugs being materially larger than the wire, could readily be driven home with a good deal of force, thus insuring an excellent electrical connection without endangering the wire.
Fig. 11.
Fig. 12.
