The buoyant mine case.—The service 32-inch pattern is made of 10-pound, ¼-inch, open-hearth steel, of great toughness and elasticity, and is thoroughly galvanized. The shell consists of two hemispheres, ribbed and welded together at the equator, thus avoiding all rivets. Every case before it is accepted is tested with an internal hydraulic pressure of 100 pounds per square inch.
The top hemisphere is provided with an external maneuvering ring; the bottom hemisphere has a hole 5½ inches in diameter at the pole. The edge of the hole is reenforced by a welded ring 1½ inches thick; and near it are four bosses, also welded, carrying screw bolts which project 2½ inches outside to secure the cap.
The cap consists of a hemisphere of 15-pound, ⅜-inch wrought iron, flanged and dished at the base to fit the case, to which it is attached by the four bolts already mentioned. They pass through slots in the flange, which is then held in place by shoes and nuts which are keyed on. The water has free access to the chamber inside the cap. The uses of the cap are: To clamp the Turk’s-head of the mine cable, to cover and protect the portion of the core exposed outside the case, and to serve as an attachment for the wire mooring rope.
A hole 1½ inches in diameter at the pole of the cap is connected by means of a slot with a 3-inch hole punched through the cap between two of the bails. This arrangement permits the entrance or removal of the Turk’s-head without removing the cap from the mine case. The mooring attachment consists of a ring of 1½-inch wrought iron, having a hole 2½ inches in diameter, attached to the cap by three bails of 1-inch wrought iron permanently double riveted to the sides. The cap is thoroughly galvanized.
Fig. 5.—COMPOUND PLUG,
OLD MODEL FUSE CAN.
Fig. 6.—COMPOUND PLUG,
RUBBER FUSE CAN.
Fig. 7.—COMPOUND PLUG,
TROTOL FUSE CAN.