WILLIAM SIEMENS, F.R.S. 



421 



" No," as the limit for steel according to the Board of Trade 

 Jea was at present (> tons compared with ."> tons for iron ; and 



w nut likely that this limit would be materially extended in 

 favour of steel for riveted work, because a certain thickness of 

 plate was necessary to prevent buckling and rapid deterioration 

 through oxidation. There was, then, at 15 tons with mild steel 

 an enormous margin of safety within the elastic limit, and a 

 vessel constructed of mild steel would be just as rigid as one 

 constructed of hard steel, using the same scantling in both cases. 

 But occasions would arise upon which a ship was bumped, and 

 then it would be strained far beyond 15 tons per square inch ; 

 and what would be the result ? If they had a ship of mild steel, 

 it would simply yield to that extreme strain ; if they had a hard 

 steel, it might break. It was, therefore, a question for the ship- 

 builder to consider. " Is my ship as a whole structure, taken as a 

 girder, to be strained beyond 15 tons per square inch, and must I 

 therefore make the plates strong enough to resist that strain, or 

 shall I limit the extreme strain of the structure to within 15 tons 

 per square inch, and have a material which, if subjected to an 

 excessive strain or blow, will yield and not break ? " He should 

 say that it was far safer to have a material that would, under 

 such circumstances, yield. He would, therefore, maintain com- 

 paratively low tests for absolute strength, which he would limit to 

 perhaps 30 tons per square inch breaking strain, whilst insisting 

 upon an elongation of at least 20 per cent, of an 8-inch bar. 

 There were other advantages connected with mild steel which 

 would be lost in using a hard material. A mild steel could not be 

 injured by sudden cooling, and it need not be annealed, but a 

 hard steel had to be annealed. If a comparatively hard steel 

 plate was punched, its strength would be diminished to a consider- 

 able extent, whereas it was fully proved that a very mild steel 

 might be punched without injuring its strength any more than by 

 drilling ; and at some of the Government yards, after careful 

 consideration of the whole subject, they had given up the practice 

 of drilling plates whenever it was found more convenient to resort 

 to punching. These arguments were all in favour of a veiy mild 

 steel. Then with regard to what fell from his friend Mr. Adamson 

 as to the bending test not being a test of elongation but a kind of 

 mixed test of elongation and solid flow, he thoroughly agreed 



