The assay of these
bodies generally resolves itself into a distillation, and, in the case
of the shales, an examination of the distillates for the useful oils,
paraffin, creosote, &c., contained in them.
Elementary carbon is found in nature in three different forms, but these
all re-act chemically in the same way. They combine with oxygen to form
the dioxide.[116] The weight of oxygen required to burn a given weight
of any form of carbon is the same, and the resulting product from all
three has the same characteristic properties. Carbon dioxide is the
common oxide of carbon. A lower oxide exists, but on burning it is
converted into the dioxide. Wherever the oxidation of carbon takes
place, if there is sufficient oxygen, carbon dioxide (carbonic acid) is
formed; this re-action is the one used for the determination of carbon
in bodies generally. The dioxide has acid properties, and combines with
lime and other bases forming a series of salts called carbonates.
The carbon-compounds (other than carbonates, which will be subsequently
considered) occurring in minerals are generally characterised by their
sparing solubility in acids. The diamond is distinguished from other
crystals by its hardness, lustre, and specific gravity. It may be
subjected to a red heat without being apparently affected, but at a
higher temperature it slowly burns away.
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