Carbon may be separated from other substances by conversion into carbon
dioxide by burning. In most cases substances soluble in acids are first
removed, and the insoluble residue dried, weighed, and then calcined or
burned in a current of air. The quantity of "organic matter" may be
determined indirectly by the loss the substance undergoes, but it is
better to determine the "organic carbon" by confining the calcination in
a tube, and collecting and weighing the carbon dioxide formed. Each gram
of carbon dioxide is equivalent to 0.2727 gram of carbon.
[Illustration: FIG. 70.]
[Illustration: FIG. 71.]
Instead of a current of oxygen or air, oxide of copper may be more
conveniently used. The operation is as follows:--Take a clean and dry
piece of combustion tube drawn out and closed at one end, as shown in
the figure (fig. 70), and about eighteen inches long. Fit it with a
perforated cork connected with a ~U~-tube (containing freshly-fused
calcium chloride in coarse grains) and a set of potash bulbs (fig. 71)
(containing a strong solution of potash), the exit of which last is
provided with a small tube containing calcium chloride or a stick of
potash. Both the ~U~-tube and bulbs should have a loop of fine wire, by
which they may be suspended on the hook of the balance for convenience
in weighing.
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