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nerally constructed of thinly rolled sheets of iron, rivetted toge-ther; and in one instance, of a wooden frame, covered over witha kind of tarpauling. But whether the gazometer be made ofiron or cloth, it is coated over with paint or tar, both out andinside, to render it completely air-tight.
This vessel is suspended, bottom uppermost, from the ceiling ofthe house in which it is, by a chain over a pulley, with a coun-terpoise, something similar to the manner in which a chandelieris hung; only the counterweight is made a little lighter than thegazometer, so as that the latter, preponderating, may alwayshave a tendency to descend.
Immediately below, there is a pit, of rather larger dimensions,lined with stone, brick, or wood. This being filled with coldwater, the gazometer is allowed to sink; but which it will not do,until an opening be made in the top of it, to allow the containedair to escape. When this is done, the gazometer, descending,soon fills with, and becomes totally immersed in, the water.
The above mentioned opening being then closed, and a firekindled in the furnace, its heat passing through the retort, * causesthe enclosed coal to give out a great quantity of gas, which (inthe shape of a brown bituminous vapour or smoke) passes fromthe retort through a pipe immersed in the pit; and, rising upwithin the gazometer, occupies its upper region, buoying it outof the water, more or less, according to the quantity of gas thatis below it. Here the gas, having come into contact with thecold water, soon loses all colour, and becomes transparent.
From the gazometer, pipes ramify in all directions of the workwhere light is wanted: These are furnished with stop-cockswherever found necessary, particularly at each aperture wherethe gas is emitted; so that by shutting the cock, the light is in-stantly extinguished, and when again opened, the gas issuing isenflamed by a taper or any other burning body, and will continueto give light, so long as there is any gas remaining in the gazo-|tieter. The mains, and some of the smaller pipes, are of castlr or.; those leading to the different apartments, are malleable iron,copper, lead, brass, tinned iron, or wood :—but all ought to havea small declivity, that the condensed tar may run off and not ac-cumulate, so as to choke up the passage. Where it is necessaryto remove the light occasionally from one place to another, someliave flexible tubes, constructed of leather, with a small spiralwire within, the pressure of the gas Outwardly not being sufficient10 keep the tube inflated when it happens to bend sharply; othersuse only a lead tube for that purpose, which serves a long timebefore it breaks.
In this operation, the whole fuel spent in decomposing the pit-coal, is by nowasted ; as the heat it yields, enters into the gazeous products, and is® towards faithfully given out when they are employed to furnish light. GilleyEssay, * ' '
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