of two small screws. Rivetting is, perhaps, the best mode, as it is not liable to shake loose by the vibration of the hammer. The spring at its shank end may be screwed or rivetted to the bracket. Mr. Edwinson considers this the better form of contact spring. The other form is made in two pieces, as shown at [Fig. 23], where two strips of hard brass are cut off, of the width of the armature, and the edges filed. A slot is then cut in the back end of the armature to receive the two brass strips, and these are soldered into it. The top strip is then bent back over the armature to form the contact-spring, the other strip being soldered or rivetted to a small bracket of angle brass. In either case a short rod of stout hard brass wire is rivetted or screwed into the free end of the armature, and to the end of this rod is screwed or soldered the metal bead, or bob, which forms the hammer or "clapper" of the bell. The next portion to be made is the contact pillar, or bracket, with its screw, as shown at [Fig. 25]. This may either be a short stout pillar of ¼ in. brass rod, about 1 in. high, tapped on one side to receive the screw, which should be fitted with a back nut; or it may, as shown in the figure, be made out of a stout piece of angle brass. The exact size and length of the screw is immaterial; it must, however, be long enough to reach (when put in its place behind the contact spring) the spring itself, and still have a few threads behind the back nut to spare. The screw
should be nicely fitted to the pillar, and the lock nut should clench it well, as when once the adjustment of the parts is found which gives good ringing, it is advisable that no motion should take place, lest the perfection of ringing be interfered with. Some makers use a "set screw" at the side of the pillar wherewith to hold the contact screw; others split the pillar and "spring" it against the contact screw; but, all things considered, the back nut gives the greatest satisfaction. When the bell is in action, a tiny spark is produced at every make and break of contact between the contact spring and this screw. This spark soon corrodes the end of the screw and the back of the spring if brass alone is used, as this latter rusts under the influence of the spark. To prevent this, a piece of platinum must be soldered or rivetted to the spring, at the point where the screw touches, as shown at [Fig. 26], and also at the extremity of the contact screw itself. It is better to rivet the platinum than to solder it, as the platinum is very apt to absorb the solder, in which case it rusts quickly, and the goodness of the contact is soon spoiled, when the bell ceases to ring. To rivet the platinum piece on to the spring, as shown at [Fig. 26], it is only needful to procure a short length of No. 16 platinum wire, say ⅛ in., then, having drilled a corresponding hole at the desired spot in the contact spring, put the platinum wire half way through the hole, and give it one or two sharp blows on an anvil, with a smooth (pened) hammer.
Fig. 28.
Fig. 29.