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

Tripod Drills. With a 3jin. Tripod Drill, a hole igin. to i|in. dia. by 4ft. deep can be bored in hard rock in from 20 to 25 minutes. Much, of course, depends upon the nature of the rock, and also whether it is solid or fissury. In the case of jointy rock, or rocks of uneven hardness, the time might be slightly increased.* The most suitable -pressure for pneumatic tools is 90 to 100 lbs. per square inch. In determining the depth of holes, spacing apart and the size of explosive charge, the engineer will be guided by the peculiar conditions of the case in hand, and the appliances available. But it should always be borne in mind that the disintegrated rock has to be re- moved ; therefore it should be blasted in pieces of such size as to be easily handled by the ordinary dredging appliances. Regard must also be had to the proximity of buildings on shore, doclç walls., river banks, etc. ; in many cases it is necessary to proceed with great caution, using only small charges of explosives at a time, so as to avoid risk of damage to such con- structions and their foundations. CHOICE OF EXPLOSIVES. In the choice of explosives the engineer or superintendent in charge of the operations will, of course, use his own discretion. Nobel’s “Dynamite” is largely used, although “Blasting Gelatine,” “Tonite,” and “ Gelignite ” have also been employed with considerable success in submarine operations. “ Blasting Gelatine ” we have found from experience to be the most powerful explosive agent, but when frozen it is, in our opinion, more dangerous to handle and more difficult to explode thoroughly. “Tonite,” when made up in water-tight cartridges fitted with connections for attaching the insulated wire from battery, is a very good explosive for submarine work, and one great advantage in its favour is that, in the event of a charge misfiring, it can be dredged up with the disintegrated rock without danger of its exploding. The “ Tonite ” cartridge cases are fitted at the end with brass glands for securing a water-tight joint, which protects the detonator from damp. These cartridges are made outside diameter, and of any length required, and 1 lb. of explosive occupies yin. in length of the case. For dispersing wrecks, where large charges are used, the explosive is prepared in metal cases with glands, as above, but made in 5 lb. cubes, and the cases are made to contain i, 2, 3, 4, or 10 of the cubes, as required, thus making 5, 10, 15, 20, and 501b. charges, two or more of which can be lashed together if larger ones are needed. A 5 lb. cube measures about 5iin. each way. Nobel’s “Gelignite.”—The advantages which are claimed for this explosive are: — 2. It is offered at the same price as Dynamite, and being more powerful it is relatively cheaper. 3. Its plasticity in the bore hole affords a distinct economy over all rigid blasting agents, whilst its explosive energy is greater than Dynamite by fully 12 per cent. 4. It is practically uninjured by damp or submersion in water fora reasonable period—a most valuable property, especially in the case of submarine blasting. 5. It is considered more economical than Dynamite. ® See foot-note on preceding page. 99