Popular Science Monthly
��701
��The balancing-chamber is a small metal bell with a tube at the top and a small hole in the side near the bottom. When the balancing-chamber is sunk, liquid is forced into the hole, the re- sultant pressure being transmitted through the pipe to the mercury indi- cator. The indicator resembles an old- style barometer, having a tall mercury column. As soon as the balancing- chamber has been sunk to the bottom of the tank the mercury- column will rise no higher; it is then necessary to balance the system by means of compressed air. This is necessary to compensate for the loss of pressure transmitted due to the length of the copper tube. A valve at the bottom of the indicator is turned so that the balancing-chamber is in direct communication with the .air-pump. A few strokes of the pump force out the liquid from the sunken chamber. Then the valve is turned back to its former position and the pressure is correctly registered on the dial by the mercur>^ column. The accompanying drawings explain the system so clearly that further elucidation is hardly necessary.
With this device it is not only possible to determine correctly the amount of water or oil in the tank — and the cali- bration of the gage can be easily trans- lated into gallons — but it can be em- ployed for determining the tonnage of a vessel by the use of a balancing-chamber in the bow and another in the stern. Both of these chambers communicate through tubing to twin dials located in a convenient place.
Two of the accompanying diagrams illustrate the manner in which the ap-
��paratus is installed for determining a ship's draft. A one-inch hole is bored in the bow a few inches below the water line when the vessel is. unloaded. If four equipments are installed instead of two — one on the port side and the other on the starboard side in the bow and the other two installed similarly in the stern, it is an easy matter by having the four gages side by side to tell whether the ship is
���The bell-like object is contained in a small tank which communicates with a hole below the water line in a ship's side. The variations in water pressure are communi- cated to the gage. The purpose of the air- pump is to balance the system for accuracy
���As the vessel sinks in the water, due to natural or accidental causes, the increased pressure
is transmitted through copper tubing to indicators in the cabin's office, the chart-room or
the engine-room, giving due warning to the officers of the ship
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