18 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[February, 



cisty of Society of Arts; — Lieutenant Denison's Notes on Concrete, 

 from papers of Corps of Royal Engineers, Journal, Vol. !, p. 

 Lieutenant-Colonel Reid, ditto, see alsu the Journal, Vol. 1, page 131; 

 a letter on concrete, by a Constant Reader, Vol. 3, page 2l>5, Vol. 5, 

 pages 5S, 276. 



I am, &c, 

 St. Ann's, Neircastle-tijJOii-Ty ne. O. T. 



WIRE ROPE LIGHTNING CONDUCTORS. 



Sir — Having seeu, in some of the recent numbers of the Mechanics,' 

 J\tagasine, a long discussion as to the priority of claim, respecting 

 the wire rope as a substitute for metal rods, in conductors, I beg to 

 call your attention to a paragraph, which appeared in a work, pub- 

 lished by Sir John Hersehel, more than 10 years ago. He says thus ; 

 that wire rope has long been used at Munich in preference to metallic 

 rods, for lightning conductors. I think this proves that the subject 

 has been long tried and practised, before Mr. M. J. Roberts brought 

 forward the subject. 



Your insertion of this will oblige 



A Subscriber. 



WROUGHT IRON AXLES. 



Sir — It is worthy of remark how slowly well proved facts, individually 

 acknowledged and acted upon, become generally admitted ; it is to be 

 regretted that we are not more communicative of those events which 

 strike us in our daily practice, and which, if announced as soon as 

 discovered, would so materially and rapidly tend to general im- 

 provement. There is, perhaps, no instance in which this can be more 

 clearly exemplified than in the use of wrought iron; it is scarcely 

 possible to refer to the subject without an example being readily laid 

 before you. Every manufacturer has had more or less his attention 

 drawn to the fact, that in its various applications wrought iron is sub- 

 ject to become brittle. Iron spindles, piston rods, fire bars, crow bars, 

 chisels, and many other things, are known to lose their fibrous quality 

 after being in use for a length of time, varying according to the nature 

 of the service they have had to perforin. By some it has been con- 

 sidered that the iron originally employed was of bad quality, and the 

 circumstance when discovered has not been otherwise attended to 

 than by replacing the broken piece ; but in many instances the phe- 

 nomena lias been clearly established, closely examined, and well 

 attended to, and that for years together, without, however, having 

 become a generally acknowledged fact, sufficiently positive to justify 

 the opinion that wrought iron, applied for certain purposes ought only 

 to be allowed to perforin a previously determined quantity of work, 

 after which it becomes requisite to re-forge the piece. 



In most cases the fracture may be unattended with danger to human 

 life, but in others, as in connexion with railways, where hundreds of 

 lives may depend on the strength of an axle, it daily becomes more 

 evident that extraordinary precautions must be resorted to for the 

 purpose of avoiding accidents, and 1 would, with regard to railway 

 axles, suggest (as a precautionary measure) the propriety of limiting 

 the distance they should be allowed to run previous to their being 

 thrown out as unfit for service, and that whether apparently in good 

 condition or not. Such is the perfection with which these axles can 

 now be manufactured, that when a suitable quantity of iron is used, it 

 may be confidently asserted that every axle turned ont of the shop 

 after due examination may be considered to be sound, and that by 

 limiting the work it is allowed to perform, the fracture of an axle 

 would become a very improbable event. 



Having been lately in Paris, I mentioned the circumstance to M. 

 Arnoux, the directing manager of the extensive works belonging to 

 the Messageries Laffite & Caillard, persuaded that from a person 

 whose attention has been for so many years engaged on this subject, 

 I should obtain some positive information ; he showed me a number 

 of axles which he had caused to be broken, after they had performed 



their allotted quantity of work ; they all broke short and brittle, the 

 fracture invariably indicating the progress of the disease. The frac- 

 mmences at the lower angle of the axle on the side of the 

 traction, which is evidently in fixed axles the point of greatest fatigue, 

 and in those axles which have given way under the weight of the 

 load, the fissure has in some instances nearly traversed the axle before 

 it broke entirely, and it is then very easy to trace the accident from 

 its engine. I will endeavour to describe its usual appearance by the 

 following diagram; the arrow shows the direction in which the car- 

 riage moves. 



The fracture invariably originates at the angle 

 a, and appears to progress at intervals by zones 

 as shown by the lines in the diagrams, the first, at 

 the point a becoming perfectly black, the colour 

 of each being lighter as they gradually extend 

 from this point, and as the contact of the two 

 sides of the fracture becomes more intimate, the 

 ( t' grain of the iron towards the angle a is coarse, 



and has a large crystalline texture, which diminishes in size as the 

 fracture approaches the angle b, at which point the metal remains 

 slightly fibrous, having evidently undergone a more rapid deterioration 

 at its point of greatest strain. 



M. Arnoux informed me, that in consequence of this effect, to which 

 he has for a long time paid great attention, he has come to the con- 

 clusion that an axle can only safely run a distance of 30,000 leagues, 

 or about 75,000 English miles ; when an axle has run that distance, he 

 invariably takes it out, places it between two new bars of iron, and 

 welds them together so as to form a new axle. If the carriage usually 

 runs over a paved road, such as is frequently met with in France, the 

 axle is not allowed to run so great a distance, and a certain degree of 

 wear in the collar then determines the period at which the axle is 

 thrown out, not in consequence of the wear of the collar, but because 

 that degree of wear has proved, by experience, that it is prudent to 

 renew the axles in order to avoid a fracture. 



Here, then, we have the proof of an important principle in the 

 application of wrought iron, being well established and long known to 

 one, and probably to many individually, without having come to the 

 knowledge of railway engineers, who are thus compelled to arrive at 

 this important truth by dint of actual experience, obtained through 

 the medium of a series of lamentable accdents, and they could not 

 acquire their information in any other way, unless made acquainted 

 with the circumstance by those who have previously purchased their 

 knowledge. 



The question, then, admitting the above statement to be correct, 

 will be, how great a distance it may be pruden; to allow railway axles 

 of different descriptions to run; and to solve this question, it will be 

 advisable, in the first instance, to adopt a term which may certainly 

 be within the limit of perfect safety, until the greatest distance that 

 can be safely adopted may have been determined by a series of well 

 conducted experiments. 



Iron exposed to great heat undergoes the same kind of deterio- 

 ration. I examined, in the same establishment, several bars taken 

 from a furnace in which they heat their wheel hoops ; the part of the 

 bar directly exposed to the fire offered the same crystalline appear- 

 ance as the broken axles, which gradually diminished towards the 

 end that was out of the fire, and the end of the bar which was out of 

 the fire altogether, had the appearance of good tough iron. The por- 

 tion which had suffered most from its direct contact with the heat, 

 having been doubled over and welded entirely, recovered its fibrous 

 quality, and stood a cold bend as well as any iron that had not been 

 in the fire. 



Should you find this communication worthy a place in the Journal, 

 you will oblige, by its insertion, 



10th January, 1843. 



Your obedient servant, 



H. H. Edwards. 



