398 THE SCIENTIFIC PAPERS OF 



would stand a breaking weight of 60,000 Ibs., except puddled steel 

 which was not the material used according to the specification, 

 and if such iron could be obtained the weight with which it was 

 to be loaded, viz., 10,000 Ibs., appeared needlessly small, being 

 equal to \ only of the total breaking weight. American engineers, 

 if the author represented them correctly, had very little confidence 

 in steel as a building material. Perhaps he might be allowed to 

 make a few remarks with regard to that material, to which he had 

 paid considerable attention. A distinction ought to be drawn 

 between steel and steel. There was a material called steel, but 

 which, in reality, was the purest iron ever introduced to the notice 

 of engineers. It contained 99*6 per cent, of metallic iron, and 

 only 0'4 per cent, of foreign matter of every description, whereas 

 the best so-called iron contained between 3 and 4 per cent, of 

 foreign material. Mild steel was really iron of the best character, 

 and he could not conceive how such a material could be thought 

 unreliable in its application. It was produced, not like puddled 

 iron, in small quantities to be welded together with the chance of 

 enclosing foreign matter, and producing irregular results ; but it 

 was produced in large masses 10 or 12 tons of fluid substance 

 and there was every probability that such a material was uniform 

 to the utmost degree. Practice had, indeed, fully substantiated 

 the fact that there was no material more uniform than that very 

 mild steel. It would bear 28 tons breaking strain to the square 

 inch, simply because it was iron, for no one would pretend that 

 cinder would bear a strain equal to that of iron. In mixing 

 between 3 and 4 per cent, of cinder with the iron, some of its 

 strength must necessarily be lost ; otherwise it had all the qualities 

 which iron ought to possess. But for engineering purposes he 

 would restrict the use of very mild steel. It was excellent for the 

 construction of boilers, and for the construction, perhaps, of con- 

 tinuous girders, because it was very reliable. It might be loaded 

 to one-half its breaking strain without any sensible permanent 

 set, and if it were loaded beyond that, it would not rupture, but 

 it would elongate to the extent of 25 per cent. ; therefore, in con- 

 structing a girder bridge of such material, the chances were that it 

 would bend down to the bottom of the river rather than break. 

 But it was not the strongest material that could be used. In the 

 New York bridge, which he saw in progress last year, the steel 



