One of the authors has examined an average
sample and has found it fully equal in every way to blacks, such as those
termed "spirit blacks," which fetch a price considerably above their real
value. It has a pure black cast of tint, is free from greasy matter, and
can therefore easily be ground into water, or into linseed oil without
interfering with the drying properties of the latter. Acetylene black has
also been tried in calico printing, and has given far better results in
tone and strength than other blacks per unit weight of pigment. It may be
added that the actual yield of pigment from creosote oils, the commonest
raw material for the preparation of lampblack ("vegetable black"), seldom
exceeds 20 or 25 per cent., although the oil itself contains some 80 per
cent, of carbon. The yield from acetylene is clearly about 90 per cent.,
or from calcium carbide nearly 37.5 per cent, of the original weight.
An objection urged against the Hubou process is that only small
quantities of the gas can be treated with the spark at one time; if the
cylinders are too large, it is stated, tarry by-products are formed. A
second method of preparing lampblack (or graphite) from acetylene is that
devised by Frank, and depends on utilising the reactions between carbon
monoxide or dioxide and acetylene or calcium carbide, which have already
been sketched in Chapter VI.
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