243. Igniters are devices for lighting gas burners, either singly or in groups, and are designed to save the time and labor which would be required to light them by hand.

A self-lighting gas burner is shown in Fig. 92. The key is so made that the gas can never be entirely shut off, and when it is turned to extinguish the light, a small amount of gas is still allowed to pass, enough to maintain a small peep of flame at the tip of the burner. In order to protect this little flame from extinction by drafts of air, it is enclosed by a cap or globe g. When the burner is in full operation, the globe drops down below the flame to the position shown; but when the lever b is reversed to shut off the gas, the link d operates to raise the globe above the top of the burner, thus shielding the little flame from accidental extinction. The lower end a is a socket, threaded and soldered to fit the ordinary fixture. The fixture to which this burner is attached must be provided with a key, as usual, so that the burner may be entirely extinguished when desired.

Details Of Fixtures 103

Fig. 92.

244. Sun lights, and other large groups or clusters of burners, are usually lighted in a similar manner. When the cluster is extinguished, one small tip is left burning, and this serves to relight the whole group when the gas is again turned on. This small burner is commonly called a pilot light, and it is supplied with gas by a separate pipe. The supply of gas to all the other burners is controlled by a single cock, so that they may be turned down simultaneously, and may be extinguished or promptly relighted whenever desired.

There are also a large number of igniting devices which operate by means of electricity. Two methods are in use: in one an electric spark is caused to flash through the stream of gas issuing from each burner, thus igniting it; in the other, a small piece of platinum wire is heated to incandescence near the tip of each burner, the electric current being turned on after the gas issues from the burners, and shut off as soon as the lights appear.

245. Safety "burners are designed to close a valve and shut off the gas when the flame is extinguished. A great many devices of this kind have been patented, but few, if any, will operate with a sufficient certainty to be worthy of confidence. Nearly all of them employ bars of metal or other substances which are expanded by the heat of the flame, and while in that condition hold the gas valve open. When the flame goes out, the expanding body contracts by cooling and permits the valve to close.

The great need for safety burners arises from the fact that when the gas supply is interrupted or shut off, every burner is extinguished, but the keys are not closed. When the gas comes on again, it streams out of each open burner, and in many instances does great damage by causing explosions or by suffocating the inmates of the building.