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82 PRECIOUS STONES.
after
heating for four hours in a reverberatory furnace, the tubes on opening
were found to be empty, owing to leakage. Later, he tried plugging with
iron balls, the upper end of the tube being narrowed after the
introduction of the ball, which was then drawn up and luted. This
method was worse than the former, not as regards leakage, but damage,
as they either burst with considerable violence or the balls were blown
out. After this, welding was resorted to. Now it is obvious that, when
three parts full of spirit, this proceeding required considerable
skill, the ends of the tubes having to be immersed in a freezing
mixture. There were many failures due to bursting whilst firing, or
very often a tube would burst with a loud explosion when being opened.
This latter operation was in almost every case very difficult, owing to
the hardening of the inner part of the tube by conversion of the iron
into steel. The mixture used by Mr. Hannay in his three successful
experiments was 4 grams of lithium in a solution of bone oil 90 per
cent, and paraffin 10 per cent., the tube being three parts full,
welded off and brought to a red heat in an inclined reverberatory
furnace for fourteen hours. The hard crystalline cake obtained yielded
minute Diamonds having all the properties of real stones and consisting
of 97-85 per cent, pure carbon with a trace of nitrogen.
Since
1893 various experiments have been carried out, and with the advance in
electricity a great power has been placed in the hands of the
experimentalist. The late H. Moissan, of Paris, obtained very
successful results with the electric furnace, and produced many
different minerals, including Diamonds over 0'5 m.m. in size. It would
be of interest as showing the time and skill required
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