Before the commercial production of calcium carbide made it one of the most easily obtainable gases, the processes which were most largely adopted for its preparation in laboratories were: - first, the decomposition of ethylene bromide by dropping it slowly into a boiling solution of alcoholic potash, and purifying the evolved gas from the volatile bromethylene by washing it through a second flask containing a boiling solution of alcoholic potash, or by passing it over moderately heated soda lime; and, second, the more ordinarily adopted process of passing the products of incomplete combustion from a Bunsen burner, the flame of which had struck back, through an ammoniacal solution of cuprous chloride, when the red copper acetylide was produced.
This second method of production has the great drawback that, unless proper precautions are taken to purify the gas obtained from the copper acetylide, it is always contaminated with certain chlorine derivatives of acetylene.
The product combines with acetylene to form rubidium acetylide acetylene, Rb2C2 C2H2, which on heating in vacuo loses acetylene and leaves a residue of rubidium carbide Rb2C2 (ibid.
This solution absorbs acetylene with the precipitation of red cuprous acetylide, Cu 2 C 2, a very explosive compound.
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