Gas Holder.
The name of gas holder, or, as it is improperly called, gasometer, is given to the vessel employed for collecting the gas and storing it up for use. In the principle and construction of this part of the gas light machinery, peculiarly valuable improvements have of late been made. They have contributed to lessen the expence of the apparatus so much, that a reservoir for storing up any quantity of gas, may now be furnished for nearly one half the sum which such a vessel cost as originally constructed.
In the infancy of the art of lighting with coal gas, the reservoir was encumbered with a heavy appendage of chains, wheel-work and balance weights, and from the construction of the machine, it was necessary to guard it from the impulse of the wind, the action of which on the gas holder, would have rendered the lights which the machine supplied with gas, unsteady.
Hence it was necessary to inclose the gas holder in a building, called the gasometer house, which formed one of the largest items of expenditure which the proprietor of a gas light establishment was called upon to defray.
Now, however, the whole of these expensive appendages is dispensed with, nor is the gasometer house to contain the gas holder any longer necessary, and the machine as now constructed may be fixed in the open air.
Gas Holder as originally employed.
The gas holder, of the original construction, consists of two principal parts; first, of a cistern or reservoir of water, usually constructed of masonry, or of cast-iron plates, bolted and screwed together; and secondly, of an air-tight vessel which is closed at top and open at bottom, inverted with its open end downwards into the cistern of water. This vessel is always made of sheet-iron plates rivetted together air-tight, and was suspended by a chain or chains, passing over wheels, supported by a frame work.
If the common air be allowed to escape from the inner vessel, when its open end is under the edge of the water in the outer cistern, it will freely descend, and water will occupy the place of the air; but if the avenue of the escape be stopped, and air be made to pass through the water, the suspended inverted vessel will rise to make room for the air. And, again, if the suspended vessel be counterpoised by a weight, so as to allow it to be a little heavier than the quantity of water which it displaces, it will descend, if, the entering gas be withdrawn through an outlet made in the vessel to permit the gas to escape. But if the outlet be stopped, and air again be admitted under the vessel, it will rise again. The apparatus, therefore, is not only a reservoir for storing up the gas introduced into it, but serves to expel the gas which it contains, when required, into the pipes and mains connected with this machine.
According to this construction of the apparatus the interior inverted vessel forms strictly what is termed the gas holder. It is suspended as already stated in the outer cistern, by a chain or chains, passing over pullies, supported by blocks and frame work, and to the chain there is affixed a counterpoise balance, of such a relative weight, as to allow the gas holder a slow descent into the water, in order to propel the gas into the mains or vessel destined to receive it, with a very small and uniform weight.