Hydrogen : Oxy-hydrogen And Oxy-acetylene Blowpipes

When oxygen and hydrogen are supplied separately to a blowpipe jet consisting

Fig: Oxy-hydrogen blowpipe

of two concentric metal tubes, the oxygen being inside, a blue, pointed, intensely hot flame is produced. Platinum wires readily melt in this flame, which has a temperature of about 2800°. Carbon monoxide instead of hydrogen gives a flame temperature of about 2600°. If the oxy-hydrogen (or oxy-coal gas) flame impinges on a small cylinder of quicklime, an intensely white light is emitted by the incandescent infusible lime, formerly used as limelight.

In the oxy-acetylene blowpipe acetylene gas takes the place of hydrogen or coal gas, and a hotter flame (3100°-3315°) is obtained. The steam formed is practically completely dissociated, and the reaction is

C₂H₂ + O₂ = 2CO + H₂

The flame is therefore strongly reducing, which makes it suitable for welding metals. In cutting iron or steel a third inner tube is used and when the metal is heated by the flame to a high temperature, this inner oxygen jet is turned on. The iron itself then burns brilliantly, emitting showers of sparks, and rapidly fuses away. The oxygen jet is narrow, and a very clean cut is produced. Plates of steel 12 in. thick can be rapidly cut through in this way. Coal gas may also be used.

The acetylene and oxygen are used in the proportions 1-5 vols. of O₂: 1 vol. of C₂H₂, the acetylene being either generated from calcium carbide and water in situ, or more conveniently used dissolved under pressure in acetone, soaked in a porous material contained in steel cylinders. (Compressed acetylene gas is liable to explode spontaneously.) The porous material may be "kapok," seed-hairs in the pods of a tree (Eriodendron anfractuosum) growing in India and Java.

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