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PRACTICAL INSTRUCTION IN THE MANAGE = MENT OF LIME=LIGHT JETS.
OXY-HYDROGEN LIGHT or limelight is produced by heating the surface of a piece of lime to a white heat by means of a flame produced by the combustion of hydrogen and oxygen. The hydrogen is supplied in several ways, and pure hydrogen is rarely used. The most general form is that of coal gas compressed in cylinders.
Another substitute for pure hydrogen that is rapidly becoming popular is obtained by passing oxygen through ether or gasoline.
Coal gas can also be used without compressing, and taken direct from the ordinary gas supply pipes.
When compressed gas is used, an automatic regulator is attached to the cylinder, in order to reduce the pressure, or a valve with a fine adjustment screw answers the same purpose, but in a much less perfect manner. Oxygen is generatlly now obtained from cylinders in the same way as coal gas. If coal gas and oxygen are mixed in certain proportions an explosion takes place if ignited. Neither coal gas or oxygen will explode if unmixed, or if there is an excess of either oxygen or coal gas beyond the explosive proportion. Should this mixture occur with our apparatus, the result can only be a startling detonation, and no danger can be experienced.
To prevent any risk of startling an audience, the operator has only to see that the proportion of coal gas is too large to allow an explosive mixture to be formed.
If the operator keeps this explanation in mind, he will be able to manage a jet with the greatest certainty.
When the oxygen and coal gas are supplied from two cylinders, the burner used is called a mixed jet. Thish as a chamber into which two gases are passed for mixing, before being passed out at the nipple where they are burnt.
The temperature of the flame varies considerably with the kind of jet used. Any disturbance of the gases in their passage causes a reduction in the temperature of the flame.
It is very essential, therefore, that the greatest care is taken in the construction of the jet and in its design.
To set up the apparatus the hydrogen cylinder is connected to the left-hand valve or tap of the jet, and the oxygen to the right. Both the valves of the jet should be kept shut till the cylinder valves are opened. To light up, open the hydrogen valve of the jet and allow the gas to blow through for a second before applying a light.
Then turn on a little oxygen till the hydrogen flame disappears, and the lime is at a state of white incandescence. Then more hydrogen can be turned on, and a further supply of oxygen. This operation may be continued until the flame slightly roars. When this effect is produced, slightly reduce the oxygen, and then the hydrogen, until the flame is silent.
A little experimenting with the proportion of the gases will soon enable the operator to get the mixture that will produce the hottest flame.