.S7A 1 WILLIAM .V/AM/A'.V.V, I'.K.S. 461 



reliable strength in every part of it, even in the lines of riveting, 

 that a material of that sort would stretch more than 20 per cent. 

 li.-i'i ire it broke, and that for that reason the unequal strain originally 

 set up in the structure would be set right by straining it. In 

 fact, he could see no reason why one-third of the breaking strain 

 should be considered as the limit to which mild steel could be 

 safely trusted. If the shell of a boiler could be rolled in one 

 piece without riveting he would advocate the use of a much 

 stronger steel, of from 85 to 40 tons, but so long as riveting was 

 i'd to he would give the preference to the milder steel, and 

 notwithstanding its mildness, would trust it to the limit of one- 

 third of its breaking strain, or, say, 8 tons per square inch, which 

 he thought, would be a safe limit. He hoped the discussion would 

 materially contribute to the obtaining of a safe but progressive 

 rule which would enable engineers to use steel not only to the same 

 extent to which it had already been applied in other countries, but 

 to a still greater extent. 



DR. SIEMENS, in explanation, said the strength of the steel 

 before punching, alluded to by Mr. Parker, was rather high for 

 the quality. The weakening by punching was very great indeed. It 

 had brought the teusile strength of the remaining metal down to 17 

 tons per square inch, whereas the bar, after being annealed, had a 

 tensile strength of 24 tons per square inch ; but even that was 

 apparently (> tons below the original strength of the bar. As 

 Mr. Campbell had remarked, punching was an art, and ought to 

 be done properly ; but he felt satisfied that, in punching mild steel 

 properly, engineers need not look for a reduction in tensile strength 

 of 24 per cent., such as the results referred to indicated. He had 

 the particulars of experiments showing that the strength of mild 

 steel was not materially influenced either way by punching without 

 annealing. In one experiment communicated to him by Mr. 

 Rendel, three bars were prepared from the same plate and in the 

 same manner. The first one was not punched at all, and it broke 

 at a tensile strain of 31* tons per square inch. When one hole 

 was punched in the middle of it, the tensile strength was reduced 

 to 30 tons per square inch. On punching two holes side by side, 

 whereby the remaining metal was more equally strained, the strain 

 \vas again brought up to 81 '65 tons per square inch, and similar 



