62 ANNUAL OF SCIENTIFIC DISCOVERY. 



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 

 manufactured. At the same time, it is stated that the compressive 

 strength is somewhat reduced. In this latter assumption I do not alto- 

 gether concur, from a permanent feature in the experiments not being 

 sufficiently taken into account namely, that in experimenting with 

 wrought iron, at a given extension, from pressure, it is necessary, 

 before you obtain even a medium value of the resistance, a modicum of 

 deflexion must take place to bring into play each of the fibres ; conse- 

 quently, not like as in a rigid cast beam, where the full action of com- 

 pression acts at once, some allowance must be made for the change 

 from the first position, in calculating the compressive forces. Assum- 

 ing generally that the increased strength of tensive power of wrought 

 compared with cast iron is 27 to 7, it at once reduces the sixfold area 

 of the bottom web of the 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, posseses 

 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 deflexion can safely take place ; therefore, both for life and prop- 

 erty its advantage is most conspicuous. With regard to the best form 

 for carrying the greatest weights with the least metal, I have come 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 lat- 

 eral action from the load. At the Belfast Iron Works the members 

 can see iron of the section shown in bars of twenty-six feet long, and 

 weighing nearly half a ton, so that it will be seen the mills are now 

 constructed so as to roll iron 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, 

 some four years ago, to read a paper at the Society of Arts on a means 

 of constructing bridges without any centering of such proportions of 

 iron, no ironmaker would attempt to produce such a proportion of 

 material, while now I have accomplished it, and would have no hesita- 

 tion in making them much larger if required. I have not a doubt for 

 warehouses, mills, public buildings, and bridges, its value will now 

 become extensively 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 beams 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 dou- 

 ble T form. This is easily accounted for, as you necessarily weaken 

 he. whole by its being requisite to introduce riveting, while a due and 

 equal resistance is offered from all parts by the solidly rolled bar. 





