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THE SCIENTIFIC PAPERS OF 



ness and cooled suddenly by plunging it in water, without losing 

 its yielding property to any great extent. Although the absolute 

 strength of this material does not much exceed that of best iron, 

 its superiority consists in its uniformity and power of yielding 

 before breaking, which makes it a safer material to be used when 

 weighted even to a point nearer its elastic limit than it would be 

 safe to go to in dealing with iron. The Board of Trade have fixed 

 upon six tons and a half as the weight allowable per square inch 

 of steel in bridge work, instead of five tons, the weight allowed 

 for iron, but this rule, which makes no distinction between steel 

 and steel, will in all probability be yet considerably modified in 

 favour of the new material. It has been mentioned in Mr. Pic- 

 ton's paper that iron, when applied to architecture, has very often 

 been hidden in order to obtain its strength without acknowledg- 

 ing its use. That it could be worked into elegant shapes he 

 proved by the productions of mediaeval times, but it appears that 

 this art of working in iron has been if not abandoned very 

 much less used, and one of the reasons is probably to be found in 

 the fact that, after the introduction of the blast furnace, wrought 

 iron was no longer produced of its former excellent quality, and 

 that there was a difficulty in working inferior wrought iron into 

 those forms which are admired in old churches, gates, &c. But 

 in mild steel we have a material which is above all others capable 

 of being put into perfect form. We have in this material not 

 only the greatest uniformity combined with the greatest strength, 

 but we have the utmost security against accident and breakage, 

 either when loaded in excess or in case of fire, and it is also 

 a material capable of being wrought into the highest artistic 

 forms. 



