ON THE MECHANICAL PROPERTIES OF STEEL. 143 



the best quality, used in the manufacture of armour-plates, by Messrs. J. 

 Brown aud Co., I avail myself of this opportunity of comparing the results 

 obtained from this iron with those obtained from the steel bars. The 

 wrought-iron bars were tested in exactly the same manner as the steel ones, 

 and were successively subjected to transverse, tensile, aud compressive 

 strains ; the results obtained from which will be found in the following ab- 

 stract, where they are compared in their several strains to the steel bars. 



The average value of C, the unit of working strength for wrought iron, 

 is about 2-25 tons, whereas the value of this constant taken for fifteen of 

 the best steel bars is 7"4 tons, so that the strength of the latter is 3y?Q- times 

 that of the former. The average value, however, of C for the whole of the 

 steel bars experimented upon is 5-921, showing that the average strength of 

 steel in resisting a transverse strain is more than 2| times that of wrought 

 iron. The mean transverse resistance per square inch for the wrought-iron 

 bars, at the elastic limit, is equal to 6 C, or 6 x 2^, or I'Si tons, which is some- 

 what greater than the resistance usually assigned to wrought-iron bars. 

 The average value of D^, for unity of pressure and section, for the wrought- 

 iron bars is -00167, whereas the value of this constant for the steel bars is 

 about -0013, showing that wrought-iron bars have a much greater flexi- 

 bility than steel bars, and, as a necessary consequence, they have a much 

 lower modulus of elasticity. Under a transverse strain the work of de- 

 flection up to the limit of elasticity is exceedingly low for wrought-iron 

 bars ; but the work expended in elongation up to the point of rupture is 

 greater than the average of that determined for the steel bars : this is o-wing 

 to the extensihiVity of the wrought iron ; for whilst the unit of elongation for 

 the average of the steel bars is not quite -05, that of wrought iron is -14, or 

 about three times greater. The same observation applies to the work of 

 compression. The average compression per unit of length is -45, whereas 

 for the steel bars it is only about '3 of an inch. 



The average breaking tensile strain, per square inch of section, of the 

 wrought-iron bars is 2b\ tons, while this average for the steel bars is 42^ 

 tons, showing that the latter are | stronger than the former. With 



a 



strain of 22| tons per square inch the wrought-iron bars had not entirely 

 lost their powers of restitution, or the power of regaining, to some extent, 

 the preceding set. 



Although the short columns underwent a large compression under the 

 action of a compressive force, yet the pressure corresponding to the first 

 visible indication of rupture is considerable, being, on an average, about 

 seventy tons per square inch, which is about two-thirds of that of hard steel 

 columns. With comparatively soft material, like that of wrought iron, it is 

 difficult to determine the exact point at which the material in such columns 

 is fractured, so that the fuUest reliance cannot be placed on the results of 

 such experiments. 



I have appended a general summary of all my experiments on steel, in 

 order that comparisons may be readily made without the inconvenience of 

 referring to the preceding Eeport. It may be stated that the experiments 

 have given good results, aud prove that steel can be produced of double the 

 strength of wrought iron ; and, at the same time, the homogeneity of its 

 structure can be depended upon. If the cost of steel be reduced and ap- 

 proximates closer to that of iron, we may soon look forward for the sub- 

 stitution of this important metal in the place of iron. 



