Mechanical properties of Metals.—By Mr. Fairbain. After some preliminary observations, Mr. Fairbairn stated that having been requested by the British Association at their last meeting to und ertake an inquiry into the mechanical properties of cast-iron, as deducted from the repeated meltings, and feeling desirous of ascertaining to what extent it was impaired or deteriorated arrangements were made for conducting a series of experiments, calculated satisfactorily to determine this question, and to supply such data and such in formation as will enable the engineer and iron-founder to ascertain with greater certainty how far these re.castings can be carried with safety, or till such time as the maximum of strength is obtained, and such other properties as appear to a'isn't the uses of this valuable and important material . Mr. Fairbairn further stated, in connection with this subject, that it was his intention to investigate another important process, which, to a considerable extent, affects the stability of some of the most important iron constructions —viz : the rate of cooling as it affects the adhesive properties of the material, and the more complete and effective process of crys- talization. On these points it is well known that a rapid rate of cooling is invariably attended with risk, that an imperfect crystalline structure is obtained, and that irregular and unequal attractions are not only present, tat they are frequently the forerunne rsof disruption, as well as exceedingly deceptive as regards appearances, or the dangerous consequences which invariably follow in cases of rapid cooling and unequal contraction. On the Form n f'Iron i<r M'alleabU Beams or Girders.—By Mr. T. M. Gladstone. It is, said Mr. Gladstone, on the application of wrought-iron beams or girders, that I propose to make some remarks by contrasting their powers and properties with those of cast-iron; to show what form of iron I conceive best adapted for such use, and to. state as a manufacturer, what may be expected of the capabilities of iron-works to produce the same beyond previous efforts, so as to meet the increased requirements of the times. It is found, that by converting iron from a cast into a malleable state, the adhesion of the fibres of the metal under tension, becomes increased from 7 to 27, and indeed much beyond that when the best quality of material is manutactured. At the same time it is stated that the compressive strength is somewhat reduced. In this latter assumption I do not altogether concur from a permanent feature in the experiments not being sufficiently taken into account—namely, that in experimenting with wrought-iron, of a given extension, from pressure, it is necessary, before you obtain even a medium value of the resistance, a medicum of deflection must take place to bring into pl ay each of th e fibres; consequently, not like as in a rigid cast beam, where the full action of com pres- sion acts at once, some allowance must be made for the chance from the first position, in calculating the compressive forces. Assuming generally that the increased strength or tensive power of wrought, compared with cast-iron is 27 to 7, it at once reduces the sixfold area of the bottom web ofthe iron beam, and nearly reduces to one-half the required sectional area throughout, yet retaining an equal strength, for every purpose. In many cases this increase of strength, enabling to reduce the weight, will fully compensate for the difference in price, so that up to this point the market and effective value of both may be said to be equal. The wrought iron beam, however, possesses this material advantage, and that is, it will always give good warning before the point of danger is reached, and this, mainly from its vastly increased deflective power—indeed, before its maximum is reached a great deflection can safely take place; therefore, both for life and property, its advantage is most conspicuous. With regard to the best form for carrying the greatest weights with the least metal, I have eome to the conclusion, from actual experiment on a large scale., that the double T section is the best, provided the flanges are sufficient to' prevent lateral action from the load. At the Belfast iron works, the members can see iron of the section sh own in the bars, of twenty-six feet long, and weighing nearly half a ton, so that it will be seen that the mills are now constructed so as to roll iron of almost any dimensions which may be required, and such bars, from the breadth of the flanges, have never before been attempted in the three kingdoms. When I had the honor, i'bui- years ago, to read a paper at the society of Arts, on the means of constructing bridges without any centreing of such proportions of iron, no iron-maker would attempt to produce such proportion of material, while now I have accomplished it, and would have no hesitation m making them much larger if required . No doubt, for warehouses, mills, public buildings, and bridges its value will now become exclusively applied and appreciated. As these bars are rolled solid throughout, on comparison I have found they will bear nearly one- third more than any made beam of equal sectional area—that is, with a beam of which the centre-rib is of plate iron, and the flanges of angle iron, and riveted thereto, and so distributed as to make the double T form. This is easily accounted for, as you necessarily weaken the whole by its being requisite to introduce riveting, while a due and equal resistance is offered from all parts by the solidly-rolled bar. [The above are abstracts from papers read belore the -. in:tr.t meeting of the British Association for the Advancement of Science. A great many excellent papers on real practical and scientific subjects, were read before the last meeting. Of course we could not publish them all, but as we deem it of interest and profit to our readers, without any continuance from week to week, we will sometimes pre- tiTit other condensed abstracts like the above.
This article was originally published with the title "Properties of Iron"