cted,
and to this fact the stone owes its brilliancy and sparkle.

~Artificial preparation of diamonds.~ Many attempts have been
made to produce diamonds artificially, but for a long time
these always ended in failure, graphite and not diamonds being
the product obtained. The French chemist Moissan, in his
extended study of chemistry at high temperatures, finally
succeeded (1893) in making some small ones. He accomplished
this by dissolving carbon in boiling iron and plunging the
crucible containing the mixture into water, as shown in Fig.
58. Under these conditions the carbon crystallized in the iron
in the form of the diamond. The diamonds were then obtained by
dissolving away the iron in hydrochloric acid.

[Illustration: Fig. 58]

2. _Graphite._ This form of carbon is found in large quantities,
especially in Ceylon, Siberia, and in some localities of the United
States and Canada. It is a shining black substance, very soft and greasy
to the touch. Its density is about 2.15. It varies somewhat in
properties according to the locality in which it is found, and is more
easily attacked by reagents than is the diamond. It is also manufactured
by heating carbon with a small amount of iron (3%) in an electric
furnace. It is used in the manufacture of lead pencils and crucibles, as
a lubricant, and as a protective covering for iron in the form of a
polish or a paint.

~Amorphous carbon.~ Although there are many varieties of amorphous carbon
known, they are not true allotropic modifications. They differ merely in
their degree of purity, their fineness of division, and in their mode of
preparation. These substances are of the greatest importance, owing to
their many uses in the arts and industries. As they occur in nature, or
are made artificially, they are nearly all impure carbon, the impurity
depending on the particular substance in question.

1. _Pure carbon._ Pure amorphous carbon is best prepared by charring
sugar. This is a substance consisting of carbon, hydrogen, and oxygen,
the latter two elements being present in the ratio of one oxygen atom to
two of hydrogen. When sugar is strongly heated the oxygen and hydrogen
are driven off in the form of water and pure carbon is left behind.
Prepared in this way it is a soft, lustrous, very bulky, black powder.

2. _Coal and coke._ Coals of various kinds were probably formed from
vast accumulations of vegetable