IRON AND STEEL 



539 



ments reveal the somewhat startling fact that, 

 frequently, kinds of iron which the mere test 

 of breaking strain would decide to be inferior, 

 actually yield for working loads a better result 

 than certain others which would be regarded 

 as superior to them. Though the softness of 

 the material has the effect of lessening the 

 amount of the breaking strain, it has the very 

 opposite effect as regards the working strain ; 

 and this for two reasons first, that the softer 

 iron is the less liable to snap ; second, that fine 

 or soft iron, being uniform in quality, can for 

 this reason also be more depended on in prac- 

 tice. Hence, the load which this description 

 of iron can suspend with safety, may approach 

 much more nearly the limit of its breaking 

 strain than can generally be attempted with the 

 harder, or in any case with the coarser sorts. 

 The author does not pretend to say what the 

 ratio of safe load should be ; but he maintains 

 that some kinds of iron experimented on by 

 him will sustain with safety more than double 

 the load that others can be trusted with ; and 

 this, especially, in cases in which the load is 

 unsteady, and the structure exposed to concus- 

 sions, as in a ship, or to vibratory action, as in 

 'a rail \v ay bridge. 



That iron or steel which is subjected to an 

 exceedingly great number of concussions, or 

 vibratory or tensile strains, and which for a 

 long time it apparently bears without injury, 

 will as a consequence of such action finally 

 break, is well known ; and equally well, the 

 fact that when under such circumstances break- 

 ing does occur, the metal at the place of frac- 

 ture presents a highly granular or else a crys- 

 talline texture. The theory has accordingly 

 become quite prevalent, that the texture de- 

 scribed is gradually induced in the iron, the 

 latter in this way becoming weakened, until 

 it breaks. On this point, however, and as the 

 result of his experiments, Mr. Kirkaldy states 

 that when iron is fractured suddenly, the crys- 

 talline appearance is invariably presented, 

 even, it would seem, if the bar or plate be at 

 the time in the condition of good fibrous metal ; 

 and that, when the fracture occurs slowly, the 

 appearance is invariably (sic) fibrous. He states 

 that in the fibrous fractures the threads are 

 drawn out, and are viewed externally ; while 

 in the crystalline fractures the threads are 

 snapped across in clusters, and are viewed in- 

 ternally or sectionnlly. From this view, it 

 would follow that the same bar or plate may 

 be fractured in one part in such way as to ap- 

 pear fibrous, and in another part immediately 

 afterward in such way as to appear granular or 

 crystalline. 



Among the other conclusions announced by 

 Mr. Kirkaldy, many simply reaffirm, or but 

 slightly modify, principles already generally 

 accepted in regard to the working and strength 

 of iron; while still others of his propositions, 

 for which space cannot here be given, are quite 

 novel. He finds that galvanizing of ordinary 

 plates produces no sensible effect on their 



strength ; and that iron and steel are rendered 

 stronger by cold rolling, and by wire-drawing. 

 Steel is weakened if cooled from a high heat 

 by plunging in water, but strengthened by be- 

 ing in the like case cooled in oil ; and the more 

 highly the steel is heated (without, of course, 

 running risk of its being burned), the greater, 

 upon cooling it by plunging hi oil, is the in- 

 crease in its strength. 



In the discussion following this paper, Mr. 

 W. Simons remarked that, in accordance with 

 the results of the experiments made, the longi- 

 tudinal fibre of iron used in shipbuilding must 

 hereafter be placed in the direction of the most 

 constant strain a principle not hitherto re- 

 garded in such construction. Mr. B. Conner 

 mentioned that, in experiments lately made at 

 Sheffield, it was observed that the steel which 

 bore the least tension the best withstood con- 

 cussion. Prof. TV. J. M. Eankine stated that 

 nngalvanized iron is really a shade stronger 

 than the galvanized, but that the latter is the 

 more extensible ; so that, in case of galvanized 

 wire-rope, what is lost in absolute tenacity is 

 made up in extensibility, the rope being through 

 this quality better able to resist a shock. 



An article of considerable length upon the 

 subject of the "Relations between the Safe Load 

 and the Ultimate Strength of Iron,' 1 ' 1 from the 

 pen of the eminent engineer, Zerah Colburn, 

 and which is valuable, as affording a condensed 

 summary of the results secured by the most 

 careful and trustworthy experimenters up to a 

 recent period, in relation to the subject named, 

 with a consideration of their applications in 

 practice, appeared in the London " Artisan," 

 for April, 1863, and will be found reproduced 

 in the "Journal of the Franklin Institute," 

 Sept. and Nov., 1863. 



In this article, speaking of Mr. Kirkaldy's 

 experimental results, then recently published, 

 and especially in regard to his proposed new 

 standard of tensile strength, Mr. Colburn says : 

 "The reduction of diameter of a bar at the 

 point of fracture serves to give a practical man 

 a good idea of the quality of the iron, but it does 

 not admit of an expression of the mechanical 

 work done in producing fracture, as do the 

 combined breaking weight and linear extension. 

 In tearing a bar in two, also, we have to con- 

 sider the permanent stretch communicated to 

 all parts of the bar alike, and the additional 

 stretch at and near the point of fracture. That 

 part of the stretching which extends uniformly 

 throughout the whole bar would, we may sup- 

 pose, be exactly proportional to the length of 

 the bar, while that part of the stretch which 

 takes place close to the point of fracture would, 

 we may also suppose, be a fixed quantity, 

 whatever might be the length of the bar. Mr. 

 Kirkaldy's specimens of iron and steel varied 

 from 2.4 to 8.2 inches only in length ; and with 

 these the ultimate elongation at fracture va- 

 ried from nearly nothing to 27 per cent, of the 

 original length, whereas longer bars would 

 have shown a proportionally less elongation. 



