subsequent to its Manufacture. 131 



The two great distinctions which exist in malleable wrought 

 iron, are known by the names of " red short " and tf cold 

 short " qualities. The former of these comprises the tough 

 fibrous iron, which generally possesses considerable strength 

 when cold ; the latter shows a bright crystallized fracture, 

 and is very brittle when cold, but works ductile while hot. 

 These distinctions are perfectly well known to all those who 

 are conversant with the qualities of iron : but it is not gene- 

 rally known that there are several ways by which the tough 

 red shot iron becomes rapidly converted into the crystallized, 

 and by this change its strength is diminished to a very great 

 extent. 



The importance which attaches to this subject at the pre- 

 sent time will not, I think, be denied. The recent accident 

 on the Paris and Versailles Railway, by which such a lament- 

 able sacrifice of human life has occurred, arose from the break- 

 ing of the axle of a locomotive engine, and which axle pre- 

 sented at the fractured parts the appearance of the large 

 crystals which always indicate cold short and brittle iron. I 

 believe there is no doubt, however, that this axle, although 

 presenting such decided evidence of being at the time of this 

 accident of the brittle cold short quality, was at no distant 

 period tough and fibrous in the highest degree; and as the 

 French Government have deemed the matter of sufficient im- 

 portance to be inquired into by a special commission, I trust 

 that some remarks on the subject will be interesting to the 

 members of the Institution of Civil Eugineers. I propose, 

 therefore, to show how these extraordinary and most import- 

 ant changes occur, and shall point out some at least of the 

 modes by which we can demonstrate the truth of this asser- 

 tion by actual experiment. 



The principal causes which produce this change, are per- 

 cussion, heat, and magnetism : and it is doubtful whether 

 either of these means per se will produce this effect; and there 

 appear strong reasons for supposing that generally they are 

 all in some degree concerned in the production of the ob- 

 served results. 



The most common exemplification of the effect of heat in 

 crystallizing fibrous iron, is by breaking a wrought-iron furnace 

 bar, which, whatever quality it was of in the first instance, 

 will in a short time invariably be converted into crystallized 

 iron : and by heating and rapidly cooling, by quenching with 

 water a few times, any piece of wrought iron, the same effect 

 may be far more speedily produced. 



In these cases we have at least two of the above causes in 

 operation, — heat and magnetism. In every instance of heat- 



K2 



