In order to avoid that the gas mains deposited under ground in public streets or other places, may not be on the one hand superfluously heavy, or as it is called thick in the metal, and consequently unnecessarily expensive, and on the other hand not too light, or too thin in the metal, so as to be liable to become injured, we shall exhibit the weight of gas mains of different bores and lengths best suited for conveying gas, now employed at the best regulated gas works in the metropolis.[50]

[50] A mile of pipe of an average diameter, laid under ground ready for conveying gas, together with taking up and making good the pavement, costs in London, about £. 1000.—And in small towns where the lights are usually less clustered together than is the case in London, and where pipes of three inches in the bore are usually sufficient, a mile of pipe complete costs about £. 700.

Bore of
cast iron
pipes.		Length
of
pipe.		Weight
of
pipe.
INCHES.FEET.POUNDS.
2 6 46
2½6 63
3 9120
4 9175
5 9248
6 9280
7 9364

PART XIII.

Gas Lamps, and Burners.

The lamps or burners for the combustion of coal gas, may be infinitely and tastefully varied. The varieties commonly employed, are the Argand burner, the Cockspur burner, and the Bat’s Wing burner.

The Argand burner, fig. 10, and 11, [plate V.], consists of two concentric brass tubes, about one and a half inch long, and seven-eighths of an inch in diameter, (the largest size burner employed.) The interval between the two tubes is closed at top and bottom. The upper part is closed with a ring of steel, it is perforated with fifteen or eighteen holes 1⁄30 of an inch in diameter. The gas enters into the cavity between the two tubes, and issues from the circular row of apertures in the steel ring at the top of the burner where it is burnt. A double supply of air within and without the flame is effected by means of the glass which surrounds the flame. The combustion of the gas is perfect when the admission of air is in due proportion to the magnitude of the flame. The height of the gas flame should never exceed three times the diameter of the flame. When the flame is too large, the light is less brilliant, and it then produces an odour, because the combustion is imperfect.

The best shape of the glass for surrounding the gas flame of the Argand lamp, is a straight tube, shown fig. 8, [plate V.], or a tube enlarged at the base, shown fig. 9, [plate V.] Fig. 10, [plate V.], is called a crutched argand gas burner, it is used for pillar lamps; fig. 11, is called a branch argand burner.