Lay on three tight bindings of the cloth tapes, all in the same direction, care being taken to avoid wrinkles. The ends of the cloth tapes are cemented down with a thin coating of india rubber cement.
Immerse the joint in the jointing-bath at 150° to 200° F. and gradually raise the heat so that in half an hour the temperature will be 320° F., at which temperature keep the joint for twenty minutes: then take it out and let it cool in the open air.
The Formation of a Joint in a Gutta percha Insulated Cable.—Having jointed the conducting wires in the manner described at [page 47], clean and dry the joint well and cover the bare conductor with a thin layer of compound. This is best done by heating a small stick of compound to nearly its melting point, and rubbing it over the bare conductor, which has been previously heated with the flame of a spirit-lamp.
Heat the gutta percha covering of both ends gently until it is quite soft, without, however, causing it to bubble or burn. Draw, then, with the fingers, the gutta percha coverings of both ends down, tapering them off until they meet in the middle of the joint; heat them sufficiently to make them adhere together.
Apply a layer of compound on the tapered-off gutta percha in the same manner as described for coating the bare conductor, and cover it with a first coating of gutta percha sheet to about half the thickness necessary to finish the joint. This is done by heating a small sheet of gutta percha, of about one-eighth of an inch in thickness, until it is quite soft, and by pressing it in that state round the joint to the required size; the greatest care to be taken to expel all the air.
The projecting lips are then cut off with a pair of curved scissors. The seam thus produced is to be rubbed with a hot iron until it is completely closed and the joint well rounded off.
Apply another layer of compound and a second layer of gutta percha in exactly the same manner as described for the first layer; care, however, is to be taken to get the seam in this second layer of gutta percha not over, but as nearly as possible right opposite to, the seam in the layer underneath.
The whole to be worked as cylindrical as possible, and to a size not exceeding the original core. The joint, so far finished, is then to be cooled with water until the gutta percha is quite consolidated.
Another, the overlapping gutta percha joint, is made in the following manner:—
Cut off the two ends of the core, so that the gutta percha and the conductor-wire are flush. Warm the gutta percha for a distance of about three inches from each of the ends with the flame of a spirit lamp, and, when sufficiently soft, push it back until it forms an enlargement. The two ends of the conductor are then to be soldered according to instructions for making joint in conductors.