not exceed 120 revolutions per hour, as when the drum revolves at a greater speed than that mentioned, extra pressure is required to work the meter, while the increased pressure causes the water to become depressed in the measuring chambers of the drum, which causes their capacity to be increased, with the result that the meter registers slow.

The gas registered is indicated on a series of enamelled dials, the pointers attached to which indicate from 100 to 100,000,000 cubic feet at each of their revolutions. These dial figures differ from those attached to a consumer's meter, inasmuch as they all run in the same direction. Attached to the index of large meters is an eight day clock, the hour hand of which is connected with a rod carrying a pencil actuated by a slight spring. On a circular plate a graduated card is fixed, and the lead pencil attached to the clock presses upon the card, and thus indicates the amount of gas produced during any part of the twenty-four hours.

Station meters should be fixed perfectly level on a solid foundation, and be provided with inlet, outlet, and bye-pass valves, adjustable overflow pipe, water gauge, an ordinary pressure gauge for both the inlet and outlet pipes, and also a differential pressure gauge.

The water-level of the station meter should always be maintained at the same height as indicated by the water gauge, by allowing a small stream of water to constantly flow into and from it.

CHAPTER XVIII.

GAS BURNErs.

HE burners in general use for illuminating purposes

THE

may be divided into the following classes: flat-flames, argand, regenerative, and incandescent; but before proceeding to describe these different varieties, it will be necessary to say a few words concerning the principles of combustion on which the amount of light emitted from burners of the flat-flame, argand, and regenerative type depends.

At the outset it may be stated that the luminosity of a gas flame such as those above-mentioned is due to the presence of carbon particles which are heated by the high temperature of the flame to incandescence. When a gas such as coal-gas, consisting of a mixture of gaseous compounds containing carbon and hydrogen is ignited in contact with a regulated supply of air, the hydrogen of the hydrocarbon is the first to unite with the oxygen of the air by reason of its great affinity for the latter element. Under these conditions the carbon with which the hydrogen was previously combined is for the moment liberated in the free state in the interior of the flame, and, becoming intensely ignited, gives rise to a development of light, the carbon particles passing subsequently to the exterior of the flame, where there is a comparative excess of air, becoming completely burnt to CO2.

The ultimate products of combustion, therefore, being

water derived from the hydrogen of the hydrocarbon, and CO2 from the carbon of the same.

When gas is burned with an insufficient supply of air, the flame becomes larger than it would normally be, and of a yellowish colour, owing to the carbon particles not being heated to the degree of incandescence which is necessary for the production of a white light, this being the result of incomplete combustion, as, instead of the carbon being entirely consumed, a large proportion passes off in

the form of smoke.

On the other hand, when gas is consumed in contact with a proportion of air greater than that which is requisite for the full development of its light-giving constituents, the fiame shortens, with a corresponding decrease of luminosity, and if the air be largely in excess, then the flame loses, to a greater or less extent, its white appearance, and assumes a bluish tint. Under these conditions the amount of air supplied to the flame is largely in excess of that required for the complete combustion of the hydrogen, and the excess of oxygen present unites immediately with its proportion of carbon, which, being burned direct, does not produce light. It follows from the foregoing, therefore, that one of the conditions necessary in order to develop the greatest possible amount of illuminating value from gas, is to adjust the amount of air supplied to the flame to the to the amount of carbon and hydrogen in the gas.

The methods of regulating the quantity of air supplied to a flame differ according to the description of burner. In the batswing and fishtail the size and angle of the apertures determine the amount of air, while in the Argand the chief regulating agency is the chimney by which the amount of air admitted is under complete control. With a poor gas a comparatively small amount of oxygen in the form of air is required, and the most suitable burners for consuming gas of this description are those with compara

tively large holes. The directive force with which the gas issues is small in proportion to the quantity passing, and as a consequence the supply of air is likewise correspondingly small.

With a rich gas, considerably more oxygen is required, and the most suitable burners for such gas are those having comparatively fine apertures, whereby the directive force of the gas is increased, and with it the amount of oxygen. Another point to be attended to in the construction of gas burners is, that the material composing the burner should be a non-conductor of heat, such as steatite, and thus keep the flame hot, as, if a material which is a conductor of heat, such as iron, be employed, this robs the burner of its heat, and lessens the intensity of combustion.

The conditions to be arrived at in the construction of a good gas-burner are, therefore, to have the burner of a nonconducting material, and to regulate the amount of air admitted to the burner according to the quality of the gas. The amount of air admitted to the burner, and the cooling of the flame, are largely influenced by the pressure at which the gas issues from the burner, for if the pressure is greater than that for which the burner is constructed, a roaring flame results, with a consequent loss of illuminating power, as the too rapid rush of gas from the burner causes a mingling of gas and air, and a consequent cooling of the flame, while the form of the flame becomes distorted. On the other hand, in flat-flame burners, the pressure at which the gas issues from the burner fulfils the important function of promoting intensity of combustion, by bringing the white-hot particles of carbon into intimate and rapid contact with the air that is necessary for complete combustion. In Argand burners this duty is discharged by the glass chimney, but with flat-flame burners it devolves entirely upon the pressure at which the gas

issues from the burner. The effect of pressure on gas flames may briefly, then, be said to be that with an excessive pressure the intensity of combustion is increased, but the separated carbon does not remain so long in the flame. As a consequence, the area of luminosity is decreased, and the total amount of light yielded is reduced. On the other hand, with an insufficient pressure, the combustion is not energetic enough to raise the carbon particles to a proper degree of incandescence, consequently the flame possesses a very feeble illuminating power, or else the carbon escapes

unconsumed in the form of smoke.

The most common defect is that of excess of pressure, and various devices have been introduced from time to time, in order to secure an uniform pressure at the burner. Flat-flame burners embrace the fishtail and batswing.

The union jet, or fishtail burner, derives its name from the shape assumed by the flame, which has some resemblance to the tail of a fish. The gas issues through two apertures, inclined at such an angle that the two currents of gas impinge against each other and spread out laterally, giving a flame at right angles to the point of exit. The diameter of these orifices varies in different burners, so as to produce flames of thickness suited to the quality of the gas they are intended to consume, as with flat-flame burners the thickness of the flame is the great factor in the utility of the burner. Fishtail burners are usually constructed of brass, while the top of the burner from which the gas issues is made of steatite, or other non-conducting material. In some burners of this type the hollow chamber of the burner is plugged with cottonwool, or small discs of fine wire gauze, the object being to lessen the pressure with which the gas issues from the burner apertures.

The batswing burner has a hollow dome-shaped top, across which a narrow slit is cut. The dome being of