Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

Missed Shot.—On no consideration attempt to withdraw the tamping, but the “tempered clay lightly squeezed in,” as described under “Tamping,” may be removed, and in its place may be put a Cartridge having a fresh Electric Detonator Fuse inserted therein. Then cover up with a lump of clay, and fire. In nine cases out of ten the missed shot will explode. If a fresh hole has to be bored, it should always be parallel to the old one, and in no case nearer to it than 6in. A missed shot in electric blasting may occur from one of the following causes, namely :— (i) Defective Exploder. (2) faulty or imperfect connections, due possibly to the wires twisted together being coated with dirt instead of being bright and clean. (3) Short cir- cuiting caused by compression of the insulation of the electric fuse wires due to damage in tamping. (4) Short circuiting by injury to the insulation of cable, or by a break in the wires. In order to determine where the defect exists, the Exploder should be immediately dis- connected and its effectiveness tested, then the cable should be tested by means of a Gal- vanometer. SIMULTANEOUS ELECTRIC BLASTING. Method of Procedure. Use Low-lension Fuses, and connect the wires in series as shown in the illustrations on page 108. If the holes are far apart a connecting wire may be used for joining the fuse wires together. The connecting wire should be of the same class and same chametei as the fuse wires. Special care should be taken that the wires at all joints have the ends clean and bright and free from dirt or grease ; they should, if necessary, be scraped with a knife. The ends of the wires where connections are formed should be covered with Chatterton’s Compound or prepared Rubber Taping as a precaution. If high-tension fuses are used in simultaneous blasting, they should be joined in 'parallel, as shown in the illustrations on page 108. Galvanometer Test.— When several holes are charged and the low-tension fuses are connected, and have the main cables attached, the machine ends of the cables should be connected with the Galvanometer in order to ascertain that there is no break in the circuit. If the needle of the Galvanometer deflects (or when the Bell-Galvanometer is used, if the bell rings) it shows that there is no break in the circuit, and that the group may be fired simultaneously with certainty. It is obvious that this test should be made by the shot-firer from the position he will occupy when actually firing the charge. All others should remove to a place of safety. CAUTIONS. Electric Fuses, especially High-Tension Fuses, which must be chemically perfect, should be stored in a dry place. Care should be taken not to “kink” or twist the fuse wires in handling or fixing so as to cut the insulation. If the insulation is cut the fuse is useless, and should be set aside. Care should be taken, under all circumstances, not to cut the insulation of the fuse wire during the process of tamping. Exploders.—Store carefully, when not in use, in as cool and dry a place as possible. Make the shot-firer responsible for the care of the Exploder, and allow him alone to handle it. Exploders, if taken care of, will last a long time in good condition. Be careful to use with High-Tension Fuses a High-Tension Exploder, and connect in parallel-, and with Low-Tension Fuses a Low-Tension Exploder, and connect in series. The only Exploder supplied as being suitable for either High or Low Tension is the Twist Exploder. Note.—There is no economy in purchasing cheap Exploders or cheap Cables. IO5