1238

THEORY AND PRACTICE OF ENGINEERING.

Book ] I.

The size of the gasometer depends upon the quantity it is required to contain : one42 feet in diameter and 23 feet in height will contain *30,000 cubic feet, and the lower

Fig. 1945.

APPARATUS TO GAS MANUFACTORY.

vessel or cistern into which it plunges is made somewhat larger, as there is usually a pres-sure allowed, which makes the water stand on the outside one or two inches higher thanwithin, which is necessary.

Before the gas is introduced into the gasometer, it is usual, after it has left the purifier,to pass it through a large revolving meter, where its quantity and temperature are exactlymeasured : some of these machines, in large works, are capable of measuring 30,000or 40,000 cubic feet per hour, and by means of contrivances attached to them, registerthe quantity as it is made, both by night and by day. Such is the gas-meter, now ingeneral use, and the section perpendicular to its axis shows its arrangement. The interiorconsists of a hollow wheel or drum, divided into four compartments by as many thinplates ; this is made to revolve freely on its axis within an air-tight case, which as well asthe lower compartments of the wheel is filled with water to a level a little above the axison which it moves :

each compartmenthas two apertures,one for admitting,the other for dis-charging the gas;and these openingsare so placed, thatwhen it enters onecompartment, itsescape must be be-neath the surfaceof the water. Thegas is admitted bythe pipe, which isbent upwards, sothat its mouth in-ternally is raised atrifle above thewater; it then flowsthrough into that

gas meter.

Fig. 1947.

Fig. 1946.

compartment which is under water, its pressure on the surface of which causes this division torise, and the cylinder to revolve on its axis; another aperture then dips into the water, and thegas is driven out as it enters, and so on in succession : the inner cylinder with its cog-wheel attached continues to turn round, and the gas passes off: it is easy to fix upon themachine a dial-plate, which indicates the quantity passed through it by one revolution ormove.

The inner cylinder is made to turn freely on the axis, passing partly through it; thisaxis is fixed at one end to the revolving cylinder, and kept steady in its motion by thecross bars; one end of the pivot is made to work in a hole drilled at the side of the pipe,by which the gas is introduced ; the other end projects beyond the inner cylinder, andreaches through the hole in the outer cylinder to a cup placed over it, which containsa hole, in which it turns ; within this cup is a cog-wheel, which works by means ofothers the hands of the dial-plate, in the same manner as a clock movement. To usethis machine water is poured into it by means of a pipe attached to the small outer cup,which regulates its height within.

The Gas Govern-jr y which modifies the pressure of the gas-holders, consists of a smallgasometer, the interior of which is in direct communication with the pipe through which