GAS-LIGHT.

564

Instead of a stopcock for letting off the gas in regulated quantities from the gas-ometer, a peculiarly formed water or mercurial valve' is usually employed. Fig-shows the modrof construction for a water trap or lute, and is, in fact, merely a g aS "ometer in miniature. c n i: f is a square cast iron vessel, in the one side of which a pil ,eA is placed in communication with the gasometer, and in the other, one with the main B'The moveable'cover (Qlid h g i k has a partition, r, m, in its middle. If this coverraised by its counterweight, the gas can pass without impediment from A to b ; but if l "counterweight be diminished so as to let the partition plate l m sink into the water, tf>communication of the two pipes is thereby interrupted. In this case the water-le Testands in the compartment A so much lower than outside of it, and in the compart» ebn, as is equivalent to the pressure in the gasometer; therefore the pipes A and Bproject thus far above the water. In order to keep the water always at the same heig*and to prevent it from flowing into the mouths of these pipes, the rim c D of the o ctvessel stands somewhat lower than the orifices A b ; and thence the vessel may be kePalways full of water.

If a quicksilver valve be preferred, it may be constructed as shown in fig. 494. A B ar s

the terminations of the two gaswhich are made fast in the rectang 0iron vessel m. e is an iron vessel °* rsame form, which is filled with quicks* ^up to the level a, and which, by me aI j sthe screw g, which presses againsbottom, and works in the fixed female sc

) lhat il)t o

vessel m may be immersed more °^ e ^- s jied

* ssage° f

c c, may be moved up or down, sovessel m may be

the quicksilver. The vessel M iswith a vertical partition m; the passag= ( ”jthe gas from A to b is therefore obstr u j c k'when this partition dips into the ? 0 fsilver, and from the gradual depressie ^the vessel e by its screw, the intervatween the quicksilver and the lowerof the partition, through which y^uj-e,must enter, may be enlarged at V‘ e * a ywhereby the pressure of the gas ‘ n nS .

be regulated to any degree. The t o

verse section of that interval is e?the area of the pipe or rather greate sbreadth of the vessel m from * an damounts to the double of that sp a ^ > or B ,its length to the mere diameter ot ' t ; t jonThe greatest height to which the p a ] S om can rise out of the quicksilver, ^ ( j,;$equal to the above diameter, an g 0 f b-case the line a comes to the p a vesse lThe vertical movement of the ou ^ j lt iop

e, is secured by a rectangular rim the

which surrounds it, and'is m . fh : n whi cbupper part of the vessel M, w, r nSt ead °\guide it moves up and down. „ ra du ate ,the lever d d, an index with a ® s cre'?’

divided into four compartments, that communicate by theinterval between this cylinder and the outer case The

plate may be employed to turn . tll de > nand to indicate exactly the m a =the opening of the valve. . 0 { g aS

In order to measure the q ua ];„)itir£ *which passes through a pip e ° ° is eB>-

factory, theatre, &c., the S as " „ u (ficie Bl ”ployed, of whose construction tJie con-precise idea may be formed 1 s the 1siderAion of fig. 495, which j ar t°strument in a section perpenaxis. • ,, a there

Within the cylindrical case ^ en ds,a shorter cylinder b b, shu ^hichand moveaWe round an a > w jth

axis?

ope " i,, ?/wluchmode i u

the

this