THE ROYAL ARTILLERY INSTITUTION. 
143 
(32) The specimens were generally found to stretch equally throughout 
their length until close upon rupture, when they more or less suddenly drew 
out, usually at one part only, sometimes at two, and in a few exceptional 
cases, at three different places. 
(33) The ratio of ultimate elongation may be greater in short than in long 
bars in some descriptions of iron, whilst in others the ratio is not affected by 
difference in the length. 
(34) The lateral dimensions of specimens forms an important element in 
comparing either the rate of, or the ultimate, elongations—a circumstance 
which has been hitherto overlooked. 
(35) Steel is reduced in strength by being hardened in water, while the 
strength is vastly increased by being hardened in oil. 
(36) The higher steel is heated (without of course running the risk of 
being burned) the greater is the increase of strength, by being plunged into 
oil. 
(37) In a highly converted or hard steel the increase in strength and in 
hardness is greater than in a less converted or soft steel. 
(38) Heated steel, by being plunged into oil instead of water, is not only 
considerably hardened , but toughened by the treatment. 
(39) Steel plates hardened in oil and joined together with rivets are fully 
equal in strength to an unjointed soft plate, or the loss of strength by 
riveting is more than counterbalanced by the increase in strength by harden¬ 
ing in oil. 
(40) Steel rivets fully larger in diameter than those used in riveting iron 
plates of the same thickness being found to be greatly too small for riveting 
steel plates, the probability is suggested that the proper proportion for iron 
rivets is not, as generally assumed, a diameter equal to the thickness of the 
two plates to be joined. 
(41) The shearing strain of steel rivets is found to be about a fourth less 
than the tensile strain. 
(42) Iron bolts, case-hardened, bore a less breaking strain than when 
wholly iron, owing to the superior tenacity of the small proportion of steel 
being more than counterbalanced by the greater ductility of the remaining 
portion of iron. 
(43) Iron highly heated and suddenly cooled in water is hardened, and 
the breaking strain, when gradually applied, increased, but at the same time 
it is rendered more liable to snap. 
(44) Iron, like steel, is softened, and the breaking strain reduced, by being 
heated and allowed to cool slowly. 
(45) Iron subjected to the cold-rolling process has its breaking strain 
greatly increased by being made extremely hard, and not by being “ consoli¬ 
dated 33 as previously supposed. 
[VOL. IV.] 
19 
