PUTTING IN THE CHARGES.
The nitro-glycerine is contained in tin cartridge cases, like mammoth candle moulds, ten feet long and from four to five inches in diameter. They are connected with the battery by wires. The divers go down and place these in the holes which have been drilled, first pulling out the wooden plugs which have been placed in them after they were drilled, to keep them from getting filled with dirt. As soon as the charges are placed, the diver returns to the boat, and it drops far enough from the spot, to be safe from the effects of the explosion, and then, with a few turns of the battery, the nitro-glycerine explodes. Two muffled explosions are heard, the one transmitted through the water and the other through the air, and on the instant a volume of water is hurled perhaps fifty feet into the air, while through the mass jets of water are hurled in all directions two or three times further, together with fragments of rock. The water subsides quickly, and round the spot dead fish come floating to the top, killed by the shock of the explosion. At each blast the rock is broken up over an area of four or five hundred square feet, and the fragments are removed by a grappling machine.
GRAPPLING MACHINE.
In these submarine operations the divers use the armor which the discovery of india rubber and the process of vulcanizing it has made possible, enabling the diver to descend, and leaving him liberty of movement enough to work. In this, as in almost every other new method, there have been gradual steps of improvement and development. During the latter part of the last century the plan was proposed for the diver to carry down with him a supply of air, compressed into a reservoir which he wore on his back, inhaling the air through a tube. Modified arrangements of this method were in use until, in 1830, the discovery of india-rubber afforded the opportunity which was immediately made use of, to improve the diving apparatus. Various improvements, some of them protected by patent rights, have been made in the construction of this submarine armor, but as perfect a method of making it as any is that designed by two Frenchmen, M. Rouquarol, a mining engineer, and M. Denayrouze, a lieutenant in the French navy. One of the chief merits of this arrangement is that by which the supply of air is furnished the diver. This apparatus the diver carries on his back, and it consists of a reservoir made of steel or iron, capable of resisting great pressure, with a chamber on its top constructed to regulate the influx of the air. A tube from this chamber, terminating in a mouthpiece, is held between the diver's teeth. This pipe is furnished with a valve permitting the expulsion of air, but opposing the entrance of water. The steel reservoir is separated from the chamber by a conical valve opening from the air chamber in such a way as to open only by the force of exterior pressure, that of the air in the reservoir tending to close it. The air from the air-pump is forced into the reservoir, and from this the diver supplies his needs as follows: The air-chamber is closed by a movable lid, to which is attached the tail of the conical valve. The diameter of the lid is a little less than the interior diameter of the chamber, and it is covered with india-rubber so as to be air-tight. It yields to both interior and exterior pressure, rising and falling as the case may be. When exterior pressure is exerted on it, the valve is affected, communication is opened between the air-chamber and the reservoir and a portion of the compressed air from the latter flows into the chamber. Should there be too much air in the chamber its pressure against the movable lid keeps the valve closed.
DIVERS DRESSED IN THE APPARATUS DESCRIBED.
When in use under water its operation is thus: The diver by drawing his breath takes air from the chamber; exterior pressure is exerted on the movable lid, it falls, causes the valve to open, and air comes from the reservoir to establish the equilibrium, when the lid rises and shuts off the communication between the air-chamber and the reservoir until another inspiration on the part of the diver repeats the action just described. When the workman expires, the valve in the respiratory tube allows the expelled air to escape into the water. This apparatus works automatically; though the air-pump may be worked irregularly, its action is regular. The diver receives just the quantity of air enough for a respiration, and this reaches him at a pressure equal to that to which the rest of his body is subjected, and he is therefore able to breathe without effort or attention. The compression of air heats it, and the breathing of air thus heated is bad for the diver. This has been remedied by the same gentleman, by the modification of the pumps by which the air is forced in the reservoir. The air is cooled by being forced to pass through two layers of water before it reaches the reservoir; and expanding in its passage into the air-chamber it becomes again cooled.
