1842.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



285 



EXPERIMENTS ON THE TENACITY OF WROUGHT IRON, 

 By James Nasmyth, C.E. 

 Sir — It may perhaps be interesting to some of the readers of your 

 Journal to have an account of the results of some experiment! which I 

 have lately been making, with a view to obtain more correct knowledge 

 of the nature of the important changes which take place in the Unacity 

 of wrought iron, when subjected to various kinds of treatment, more 

 particularly as regards the employment of wrought iron in the case 

 of railway axles, &c. At all times, any addition to our knowledge of 

 the nature of those causes which induce changes in the tenacity of 

 wrought iron, ought to be considered as a subject of much importance, 

 seeing that in so many cases our lives depend on the tenacity or 

 strength of a piece of that material. This subject has, however, of 

 late become infinitely more important, on account of the truly wonder- 

 ful success and extension of the railway system, and as the whole of 

 that vast improvement, in consequence, rests its success on the strength 

 and tenacity of wrought iron, any addition to our knowledge on that 

 subject cannot, I trust, but be considered of value. 



The subject has, however, received much additional interest, on 

 account of many theories and much controversy, which has arisen in 

 consequence of an opinion which has been given forth from rather a 

 prominent quarter, viz. the French commission appointed to investi- 

 gate the causes which led to the late disastrous accident on the Ver- 

 sailles railroad. The most remarkable part of the conclusions 

 which that body gave forth, was in substance this : — namely, that 

 however tough and strong a railway axle might originally be as it 

 came from the hands of the maker of the said axle, that the very fact 

 of its being caused to revolve day after day in connexion with the rails, 

 would ere long, through the agency of some mysterious electrical ! or 

 magnetical influence, have its nature, as regards the toughness or 

 tenacity of the iron, so impaired, as to become at length totally unsafe 

 and unfit for use. 



A more truly alarming and uncomfortable doctrine could not have 

 been produced than this, inasmuch as we should never be able to 

 know when the point of unfitness was attained, except through the 

 occurrence of one of those disastrous and melancholy accidents which 

 have but too certainly attended the breaking of a railway axle; and 

 as the above opinion was based on conjecture as to the supposed 

 influence of the most dark, hidden, and mysterious of all nature's 

 agents, we might therefore have groped about in vain for such a 

 knowledge of the subject as would be most likely to prevent such 

 dangerous changes taking place in the tenacity of the iron ; and more- 

 over, by having our attention diverted to so ;io«-understandable a class 

 of natural causes, we should be likely to cease to search for the cause, 

 cure, and prevention (which I trust my experiments will go to prove, 

 have more intimate connexion with our workshops and workmen, than 

 with philosophers and their laboratories) ; and as the results of the 

 experiments I have made on this subject are applicable to the treat- 

 ment of wrought iron generally in reference to its every day use, I 

 trust that the results may be found of practical value, the more so as 

 they go to prove that we have the cure and prevention entirely at our 

 command, without calling for the slighest additional labour or expense 

 in the treatment of wrought iron. 



From former practical experience in the working of iron in the 

 process of forging, I had always observed that, however tough, tena- 

 cious, and excellent in quality a piece of wrought iron might originally 

 be, that, by certain treatment, that tenacity might be all but entirely 

 destroyed ; and as such treatment is very frequently absolutely neces- 

 sary in the forging of wrought iron into certain forms, the knowledge 

 of how to remove the bad effects consequent on such, became impor- 

 tant to know. I am happy to state that this knowledge is so 

 simple and easily put in practice, that I trust, in future, no piece of 

 forged wrought iron will henceforth be applied to its purpose without 

 having been passed through so simple and salutary a process, which 

 you will find requires neither skill, labour, or cost worth naming. 

 Having made these observations, I shall now proceed to work. 



It either is or ought to be known to all practical men concerned in 

 Vol. v.— No. 60.— September, 1842. 



the working of wrought iron, that if a piece of the very best and tough- 

 est iron is hammered in the process of forging until it ceases to be 

 red hot, that the effect of such cold hammering, as I may term it, is to 

 cause the iron to become so brittle, that it will in many cases break 

 across in the process; or if it does not at that time, this process of 

 cold hammering has so removed and destroyed its tenacity, as to 

 render it capable of being broken with the slightest blow ; in order to 

 prove this by direct experiment, 1 took a bar of the very best wrought 

 iron, li inch square, and subjected it to the following experimental 

 tests : — 



Experiment 1. 



A bar of the very best li inch square wrought iron, at temperature 

 60°, was laid over the edge of the anvil, thus, Fig. 1, the end projecting 



Fig. 1. 



about 2i or 3 inches over at A ; with 9 heavy blows of a large sledge 

 hammer it broke off short, as indicated in the figure, the fracture ex- 

 hibiting that clear crystalhne texture due to a good quality of iron 

 at that temperature. 



Experiment 2. 



Part of the same bar of iron was taken and heated red hot, and 

 hammered till it was nearly quite cold ; when it had arrived at tem- 

 perature 60" (same as the first experiment), it was placed on the anvil 

 with the end overhanging as before, at A, cue slight blow broke it 

 sharp and square across, the fracture exhibiting a most beautiful close 

 crystalline grain, more like the fracture of steel than iron, but such a 

 fine grain as would (and indeed very frequently is) considered a proof 

 of good quality, that is, fitness to be trusted to ! So much for the 

 appearance of the texture as a criterion of fitness. Here, then, we 

 have distinct proof, by this experiment, that we have reduced the 

 blow or shock-resisting quality of the iron fully ^ by the effect of cold 

 hammering alone ; and what renders the knowledge of the effects of 

 such a process the more important is, that in most cases we shall find 

 that, in order to give the piece of forged work the requisite finish and 

 fine surface, as they come from' the hands of our workmen in that 

 department, that this very cold hammering and swaging, as it is 

 termed, is required, the more so as it is by such a process that iron 

 forgings are so finished/roni the hammer, so as to require the least pos- 

 sible labour after, and as every good workman in that department is 

 anxious to turn his work out of hand with the very best surface on it, 

 which this cold hammering enables him to do, it is not a very easy 

 matter, and (as I will soon show) not at all desirable, to require them 

 to discontinue the practice, which many have endeavoured to do from 

 want of a full knowledge of the subject. There is nothing inherently 

 wrong in this practice of cold hammering— fs.r otherwise ; the evil 

 rests with the applying such a cold hammered piece of forge work to 

 its purpose without having been passed through the curative process, 

 which is simply this, namely, to heat the piece of forged work in 

 question to a dull red heat, and lay it down to cool at its leisure. The 

 value of this most simple process will be well illustrated by Ex- 

 periment 3. 



Experiment 3. 

 A piece of the same bar iron as employed in the preceding experi- 

 raents was, after being heated red hot and hammered till cold (which 



2 R 



