Facts about Iron. 421 



Dr. Percy a specimen of black slag, not unlike iron slag, 

 lately found in " very ancieut Sinaitic remains, conjectured to 

 be anterior to the time of Moses." 



Many of tlie iron ores now worked in this and other 

 countries would not have suited the early processes, nor would 

 they, in many cases, have disclosed their character to the 

 imperfect science of early times; but, notwithstanding this 

 fact, which would operate in favour of bronze in certain 

 localities, it still remains for the antiquary to explain why 

 nations who were acquainted with iron should have resorted to 

 an expensive and, as we should think, imperfect substitute for 

 a metal that we now regard as a prime necessity of civilized 

 life. 



Of all the substances which modify the character of iron, 

 carbon is the most important, enabling it, according to circum- 

 stances and treatment, to become hard, elastic, or brittle. The 

 mode of the existence of carbon in its compounds with iron is 

 by no means well understood. Dr. Percy states that it is 

 partly determined by the conditions under which the metal is 

 heated and cooled, at temperatures very far below its melting 

 point ; and he adds that, " Professor Abel, of the Arsenal, 

 experimented on this point a few years ago, and found that 

 hardened steel wire dissolved in hydrochloric acid without 

 residue ; whereas the same steel in the softened state yields by 

 such action a dark flocculent carbonaceous residue when acted 

 upon by the same acid." Steel, in its three states known as 

 "blistered," "tilted," and "hardened," yields a different residue 

 or solution. It seems, on the whole, to be proved that carbon 

 may exist in iron in the state of mechanical diffusion, and also 

 in a state of chemical combination ; but neither Percy nor any 

 other chemist has succeeded in throwing much light upon the 

 carbides of the metal. It is very curious that hammering 

 should affect steel so as to change the propertion of its carbon- 

 aceous residue in acids, but " Caron found that rolled steels, 

 cceteris paribus, yielded a larger amount of carbonaceous residue 

 than hammered steels." In this case the mechanical force 

 exerted in hammering seems to have passed into the state of a 

 chemical force, by which the condition of the carbon was 

 changed. Polling, as a less disturbing action of mechanical 

 force than hammering, produced less effect. 



Dr. Percy, though fully believing in the influence of me- 

 chanical force as just described, throws some doubt on the 

 amount of action usually ascribed to blows or vibrations in 

 rendering iron brittle, and he is not satisfied that it induces a 

 crystalline structure. As this question enters so largely into 

 safety of railway travelling, it is hoped that it will receive 

 thorough investigation. Pending this, we may remark that the 



