7IO 



NATURE 



[February 26, 1920 



The substances tested 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, etc. After each shot the bullet and sur- 

 rounding steel were drilled out, and the chips and 

 entrained matter analysed. Fig. 5 shows the bullet 

 in the hole after firing. 



Several experiments were also made with a bridge 

 of arc-light carbon placed over the hole and raised 



MUZZLE OF -303 niri^ 



Fig. 4. 



to the limit of incandescence by an electric current, 

 and the shot fired through it into the hole at the 

 moment the carbon commenced to vaporise, as ob- 

 served in a mirror from without. Also, an arc between 

 two carbons was arranged to play just over the hole 

 and the shot fired through it (Fig. 6). The residues 

 were in all cases exceedingly small, and there was no 

 evidence of any incipient transformation of carbon in 

 bulk into diamond that could be detected by analysis. 

 The pressure on impact of a steel bullet fired into 



• MUZZLE OF -303 BIFLE 





0125 in. at the bottom. The mild steel bullet was 

 deformed by the tapered hole, which greatly in-creased 

 the velocity imparted to the nose. Progressively 

 increased charges were used. With the go per cent, 

 excess charge the block always split on the first shot, 

 but this probably occurred after impact, and not until 

 the full instantaneous pressure had been exerted, 

 which was probably about 5000 tons per square inch, 

 or about equal to that at the centre of the earth. 



It would be interesting to repeat some of these 

 experiments on a larger scale. With a projectile of 

 6 in. or 9 in. in diameter and a velocity of 5000 foot- 

 seconds, the instantaneous pressure would be the 

 same, but its duration (which is proportional to the 

 linear dimensions) would be increased from twenty- 

 to thirty-fold. It has been estimated that the rise 

 in temperature due to adiabatic compression of in- 

 candescent carbon when subjected to 2000 tons per 



Muzzle of -303* rifle*1 



FiG. 6. 



square inch is of the order of about 1000° C, so that 

 actual melting of the carbon would probably have 

 occurred when the shot was fired through the 

 incandescent carbon bridge. 



.■\nother experiment was arranged which would 

 ensure that carbon should be subjected to an extremely 

 high temperature concurrently with a high pressure ob- 

 tained by the rapid compression of the hottest possible 

 fiame, tJiat of acetylene and oxygen, with a slight 

 excess of the former to provide the carbon. The 

 arrangement was as follows (Figs. 7 and 8) : — A very 

 light piston made of tool-steel was carefully fitted 

 to the barrel of a gun of 09 in. bore ; the piston was 

 flat in front, lightened out behind, and fitted with a 

 cupped copper gas-check ring, the cup facing forward ; 

 the total travel of the piston was 36 in. To the 



originjil hole 



eCFORE FIRING 



bullet nrrt* 



FIBING 



Fig. 5- 



a hole in a steel block which it fits is limited by the 

 coefficient of compressibility of steel ; with a velocity 

 of 5000 foot-seconds it is about 2000 tons per square 

 inch. Measurements made from a section through 

 the block and bullet (Fig. 5) showed that the mean 

 retardation on the frontal face after the impact until it 

 had come to rest was about 600 tons per square inch. 

 Several experiments were made by substituting a 

 tungsten steel block hardened and tempered, and a 

 hole tapering gently from 0303 in. at the mouth to 



NO. 2626, VOL. 104] 



Fir.. 7. 



muzzle of the gun was fitted a prolongation of the 

 barrel formed out of a massive steel block, the joint 

 being gastight ; the end of the bore in the block was 

 clos«l bv a screwed-in plug made of tempered tool- 

 steel, also with a gastight collar. A small copper 

 pin projected from the centre of the plug to give a 

 record of the limit of travel of the piston. The gun 

 was loaded with '2 drams of black sporting powder, 

 which amount had been calculated from preliminary 

 trials. The barrel in front of the piston was filled 

 with a mixture of acetylene and oxygen. It was esti- 

 mated that this mixture would explode when the piston 

 had travelled about half-way along the bore. When 

 fired, the piston travelled to within \ in. of the end, 

 as had been estimated, giving a total compression ratio 



