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Ch. 7: Boart, Carbonado, & Graphite

Ch. 7: Boart, Carbonado, & Graphite Page of 171 Ch. 7: Boart, Carbonado, & Graphite Text size:minus plus Restore normal size   Mail page  Print this page
DIAMONDS
to ascertain approximately the temperature at which they were formed, or to which they have subsequently been exposed. Sprouting graphite is a form, frequently met with in nature, which on moderate heating swells up to a bulky, very light mass of amorphous carbon. Moissan has found it in blue ground from Kimberley ; my own results verify his. When obtained by simple elevation of temperature in the arc or the electric furnace graphites do not sprout ; but when they are formed by dissolving carbon in a metal at a high temperature and then allowing the graphite to separate out on cooling, the sprouting variety appears. The phenomenon of sprouting is easily shown. If a few grains are placed in a test-tube and heated to about 1700 C, the grains increase enormously in bulk and fill the tube with a light form of amorphous carbon.
The resistance of a graphite to oxidising agents is greater the higher the temperature 84
Ch. 7: Boart, Carbonado, & Graphite Page of 171 Ch. 7: Boart, Carbonado, & Graphite
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