220
EXPERIMENTS ON THE
in the block. The velocity with 90 per cent, excess charge was estimated to be about 5000 ft. per sec.
The
substance to be compressed was placed either at the bottom of the hole
when the coned-nose bullet was used, or over the mouth of the hole when
the cupped-nose bullets were used. Some of the bullets were of mild
steel, but those with cupped noses were of tool steel.
The
substances placed in the hole included graphite, sugar carbon,
bisulphide of carbon, oils, etc., graphite and sodium nitrate, graphite
and fulminate of mercury, finely divided iron and fine carborundum,
olivine and graphite. After each shot (Fig. 7) the bullet and
surrounding steel were drilled out, and the chips and entrained matter
analysed.
Several
experiments were also made with a bridge of arc-light carbon just over
the hole, raised to the limit of incandescence by an electric current,
and the shot fired through into the hole at the moment the carbon
commenced to vaporise, as observed in a mirror from without. Also an
arc between two carbons was arranged just over the hole (Fig. 8) and
the shot fired through it. as also through a crucible of carbon with a
very thin bottom containing a little molten highly carburised iron.
Of
all these experiments the only ones that yielded a reasonable amount of
residue were one made with graphite wrapped in tissue paper, the
bullet, however, in this case grazed the side of the hole, thus
producing some molten iron by the friction; and the shots through the
incandescent bridge, where again some molten metal would probably
occur. The residues were in all cases exceedingly small and not more
than would be produced from a small amount of iron melted, carburised
and quickly cooled. There was no evidence of any incipient
transformation of carbon in bulk into diamond that could be detected by
analysis.
A
bullet was also fired into a long hole, 0-303 inch in diameter, bored
in a steel block and filled with acetylene gas, retained by
gold-beaters' skin over the mouth, thus repeating the flame experiment
(but in this case without oxygen) on a small scale with the intensest
pressures available. The residue was nil.
The
pressure on impact of a steel bullet fired into a hole in a steel block
which it fits is limited by the coefficient of compressibility of the
steel, and with a velocity of 5000 ft. per sec. is about 2000 tons per
sq. inch. Measurements made from a section through the block and bullet
(Fig. 7) showed that the mean retarding force on the frontal face,
after impact till the bullet had come to rest, was about 600 tons per
sq. inch.
Several
experiments were made by substituting a tungsten-steel block, and a
hole tapering gently from 0-303 inch at the mouth to 0-125 inch at the
bottom, and using a mild steel bullet, which on entry would be deformed
and a greatly increased velocity imparted to the nose. Pro-
