CHANNEL DEMARCATION.
259
washer and purifier the gas is freed from carbonic acid and sulphur, im-
purities which are not only detrimental to a good gas, affecting the illuminating
power, but which, moreover, form an injurions deposit in the fittings,
regulators, and burners. The gas, when pure, passes through a meter to be
registered, and thence to the gasholder.
The compressors are double-acting pumps worked by steam or hand.
Fic. 227. —Gas Buoy.
Before the gas is passed into the welded, high-pressure storeholder, it passes
through a small vessel and there deposits some hydrocarbon, which is drawn
off by a small valve.
The storeholder is placed within the buoy to be lighted, where it is con-
nected with the burner, and supplies it with gas for periods ranging from
two to six months, without further attention.
In the case of gas buoys a special form of construction is rendered