S/A WILLIAM SIEMENS, F.R.S. 



407 



in fuct to furniture and stores, and it is probable that a 

 conflagration would remain confined within very narrow limits. 

 If liy concentration of flame the heat should nevertheless reach a 

 hiirh point in any portion of the building, the steel when heated 

 dness would certainly deflect to an enormous extent before 

 giving w;iy, ;uid the same indication which the fire brigade men 

 receive in the case of wood they would have in probably a still 

 greater measure in dealing with steel. But an almost complete 

 protection of the steel employed in structures would be obtained 

 by constructing the floors of girders filled in between with plaster 

 or cement, a method which is more largely resorted to in France 

 and other portions of the Continent than in this country. In 

 employing steel in the construction of columns the metal may be 

 conveniently rolled in the section of a cross and be enclosed in a 

 casing of plaster or cement, which latter will in that case fulfil 

 the double purpose of protecting the steel against accession of 

 heat and of lending itself to such structural effect as the architect 

 may desire to produce. In making large girders of steel, riveting 

 has to be resorted to, and the quality of steel that should be used 

 for such purposes differs widely from the harder and stronger 

 description of material applicable for tie rods, rolled rafters or 

 columns. These harder descriptions of steel would lose strength 

 in an extraordinary degree through break of continuity such as is 

 necessarily produced by punching and even drilling for the intro- 

 duction of rivets. Although steel is immensely stronger than iron, 

 it is more apt to tear from a point of discontinuity, and this 

 liability to tearing action in steel increases with its strength. By 

 careful annealing, risk from this source may be reduced ; but an- 

 nealing itself is a delicate and therefore risky operation, and no 

 work would be safe that depended upon its due accomplishment. 

 The steel-maker of the present day is not at a loss, however, to 

 supply a material combining extraordinary toughness with a 

 strength still greatly exceeding that of iron. This " mild steel," 

 which has recently nearly expelled iron from naval construction, 

 has an absolute strength of about thirty tons per square inch, but 

 its toughness is such that if a bar of eight inches in length is 

 subjected to increasing strains it assumes a length of ten inches 

 before giving way. Nor is this toughness dependent upon previous 

 annealing ; on the contrary this mild steel may be heated to red- 



