of ash. The rest may be
considered carbon. Carbon heated with metallic oxides takes the oxygen;
at low temperatures it forms carbon dioxide, and at higher ones, carbon
monoxide. Other conditions besides that of temperature have an influence
in producing these results; and as the quantity of charcoal required to
complete a definite reaction varies with these, it should be calculated
from the results of immediate experience rather than from theoretical
considerations.
~Flour.~--Ordinary wheat flour is convenient in use. On being heated it
gives off inflammable gases which have a certain reducing effect, and a
residue of finely divided carbon is left. It is likely to vary in the
quantity of moisture it contains. Two parts of flour should be used
where one part of charcoal would be otherwise required.
~Tartar.~--This is crude hydric potassic tartrate; the purified salt,
cream of tartar, may be used. On being heated it gives off inflammable
gases, and leaves a residue formed of potassic carbonate mixed with
finely divided carbon. Five parts of tartar should be used in the place
of one of charcoal.
~Anthracite~ or ~Culm~ is a kind of coal containing 90 per cent. or more
of carbon. It gives off no inflammable gas. It is denser, and takes
longer in burning, than charcoal. Its reducing effect is little inferior
to that of charcoal.
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