The Blow-Through Jet.
I fastened it by means of wire to the pin of the jet, and then very gradually heated it, first with the coal-gas flame and then turned on the oxygen, little by little, to obviate its breaking to fragments with the heat. With a little care I was enabled to get a splendid light and all was well, but I should recommend my friends to always see they have good limes, and not rely on finding marble mantlepieces at their disposal.
The simplest form of jet is that known as the "blow-through." In this case, a pipe carrying the hydrogen or coal-gas terminates in front of a pin holding the lime cylinder, and another pipe carrying the oxygen ends with a small nozzle in the centre and slightly below the surface of the hydrogen pipe. We use the term hydrogen, but coal-gas, which consists mainly of hydrogen, is used in preference, because it gives some light in itself, and moreover may be obtained through attaching a flexible tube to any ordinary gas supply. A bent union, such as illustrated, is a convenience, because this can be substituted for the gas burner, and the flexible tubing is easily attached.
The coal-gas being lit, the oxygen tap is turned gradually on, and the mixed gases impinging on the lime make it incandescent. It has been found, however, that the heat of the burning gas, and consequently the light given, is enormously increased if the oxygen and hydrogen are perfectly mixed together before they play upon the lime, but, as such a mixture is highly explosive, it is manifestly impossible to mix the gases in any but the smallest quantities, the explosion of which could not do any damage. This is effected by means of various forms of jets, known as the " Mixed Gas Jets " and " Ejector Jets." The gases under pressure are kept in separate cylinders under equal pressures by means of regulators, and are brought to separate tubes on the jets. In the " Mixed Jets " is a small chamber where the gases mix, and the more or less perfect mixing ensures the greater or less light. Consequently, great ingenuity has been effected in the formation of these mixing chambers on the best jets, because oxygen is sixteen times heavier than hydrogen, and, therefore, a kind of gas emulsion has to be made, and this emulsion is forced under pressure from the nozzle of the burner. In the case of the " Ejector Jets " the mixture is made by passing the oxygen through a fine orifice into the midst of the hydrogen, which it churns up and forces from the jet on to the lime. With all jets it is preferable to turn on the hydrogen tap first, and after lighting the gas, allow it to play on the lime for two or three minutes to warm it, then turn on the oxygen tap gradually. The light will increase in intensity up to a certain point and then commence to diminish. When this occurs,turn the hydrogen tap a little further to give more gas, and afterwards again increase the pressure of the oxygen. By adjusting the taps in this way, it is an easy matter to obtain the maximum light that the construction of the jet will allow. The distance of the lime from the jet is also a matter of importance. With " blow-through " jets it is usually found that the lime may be nearly touching the jet. With high-power jets the maximum light may need the lime further away, and as the lime is usually mounted on a rod, which can be adjusted for distance as well as revolved, a trial of various distances will soon enable the operator to see which is best for his purpose. The lime must be revolved from time to time, because it is gradually consumed, and the pit formed by the flame in its surface is apt to deflect the flame outwards and result in a cracked condenser, if this precaution is not taken. When turning off the light it is better to turn off the oxygen first, and sometimes there is a small crack or miniature explosion, due to the firing of the gas in the burner itself, but this is a matter of no consequence and need not cause alarm.
A bent Union for taking Gas from ordinary bracket.
The Mixed Gas Jet.
For those using the oxy-hydrogen light there is nothing for convenience equal to cylinders, and these, under the Board of Trade regulations as to testing and filling, may now be regarded as perfectly safe.