Oxy-hydrogen limelight.

Directing a flame produced by burning hydrogen (or coal gas) in conjunction with oxygen onto a cylinder of lime produces a bright white light.

There are two main types of jet or burner:

• Blow-through

  In this type, also known as the safety jet, the gases do not meet until close to the jet nozzle. It was easy and convenient to use as a normal gas fitting in a house or hall, could be used. For these reasons it was very popular with amateurs. The oxygen had to be under pressure.

• Mixed Jet

  The gases are combined in a cylinder below the jet. This gave a more powerful light but required more care and was mainly used by professional lanternists. Both gases had to be under the same pressure

In early years oxygen was often produced by the lanternist by a process using chlorate of potash and manganese black oxide, the resultant gas was captured in a bag. Later, by the late 1880s, oxygen was available commercially in cylinders. Hydrogen gas could also be produced by the lanternist using a process involving dilute sulphuric acid and zinc. It was also available commercially in cylinders, or bags could be filled from the house supply. Bags were generally 3 x 2 x 2 feet and wedged shaped. In use the bag was put under pressure by placing it between boards with a heavy weight on the top. Where both gases were in bags a double set of boards were used, this ensured the pressure on each bag was the same.

The lime cylinder has to be turned to avoid pitting, a cog wheel arrangement was usually provided for this. If mounted on a spindle with multi-start thread turning the lime would also raise it.

Taps, fittings and cylinders were colour coded (in Britain: black for oxygen, red for hydrogen, in addition hydrogen cylinders had a left-hand thread) to ensure the correct gas was connected.

These jets were used in conjunction with an acetylene generator. They came into common use at the end of the 19th century. Several, compact, generators were sold by photographic suppliers, these connected to the burner by a rubber tube. Acetylene was produced by a reaction of water with calcium carbide.

Photographic 'White Flame' carbons, 10 mm by 6". Box.