The motion of the turbine is employed to rotate
screens, coloured glasses, or any desired optical arrangements round the
flames; or, in other situations, periodically to open and close a cock on
the gas-main leading to the burners. In the latter case, a pilot flame
fed separately is always alight, and serves to ignite the gas issuing
from the main burners when the cock is opened.
Another use for acetylene, which is only dependent upon a suitably
lowered price for carbide to become of some importance, consists in the
preparation of a black pigment to replace ordinary lampblack. One method
for this purpose has been elaborated by Hubou. Acetylene is prepared from
carbide smalls or good carbide, according to price, and the gas is pumped
into small steel cylinders to a pressure of 2 atmospheres. An electric
spark is then passed, and the gas, standing at its limit of safety,
immediately dissociates, yielding a quantitative amount of hydrogen and
free carbon. The hydrogen is drawn off, collected in holders, and used
for any convenient purpose; the carbon is withdrawn from the vessel, and
is ready for sale. At present the pigment is much too expensive, at least
in British conditions, to be available in the manufacture of black paint;
but its price would justify its employment in the preparation of the best
grades of printers' ink.
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