ON THE MECHANICAL PROPERTIES OF STEEL. 141 



measvired by about | of the whole deflection, showing that this load was 

 considerably within that requisite to produce rupture. Owing to the high 

 flexibility of the haematite bars, their modulus of elasticity is low. It may 

 be here worthy of observation that, for bars of the same length, the modulus 

 of elasticity varies inversely as the coefficient (DJ of the deflection for 



unity of pressure and section, that is, E oo — -. 



These bars underwent a great elongation by a tensile strain, and a large 

 compression by a compressive strain, the average elongation being, per unit 

 of length, -0792, and that of compression •41 9 ; whereas these numbers for 

 the other bars, before experimented upon, did not, on an average, exceed 

 •06 and -355 respectively, showing the flexibility and superiority of this 

 steel in its powers to resist impact. The average tensile resistance of the 

 bars is about 3-5 tons per square inch, whereas the resistance for the other 

 Bessemer bars, before experimented upon, was about 42 tons ; so that the 

 tensile strength of the latter is 4 greater than that of the former. 



The quality of hardness of steel and wrought iron may be comparatively 

 measured by the amount of extension under a given tensile strain, and the 

 amount of compression under a given compressive strain. Applying this 

 test to the results of the experiments on the various steel bars, we find that 

 the hardest bars are the strongest, irresj[>€ctlve of the companies hij whom they 

 were manufactured. We find, for example, that the elongation per unit of 

 length for eight of the best Bessemer bars did not exceed -018, and the 

 compression per unit of length did not exceed -25. These bars had a 

 temper probably exceeding that of spring-steel, and less than that for tools. 

 The haematite bars are of a totally diff'erent description of steel from that 

 manufactured for springs and tools, and this accounts for their compara- 

 tively low powers of resistance. 



The experiments first made upon the haematite steel are anomalous. The 

 first bar experimented upon showed great powers of resistance, but the last 

 two gave results inferior to those obtained by the last experiments. At the 

 same time the value (D,) for unity of pressure and section, ia the first exjie- 

 rimeuts, is somewhat below the general average of the results of all the 

 other experiments, thereby giving a considerable value to the modulus of elas- 

 ticity. I suspect that the temper of the first bar was high ; but Avhether the last 

 two bars had a temper too high or too low, I am at a loss to determine. If 

 it is desirable to have full justice done to the haematite steel bars as to their 

 powers of resistaiice, a series of bars of the same degree of hardness as to 

 the first bar mentioned, which gave considerably more than average powers 

 of resistance, should be made, in order to compare with the harder descrip- 

 tions of steel, as exhibited by other makers — numbers of which have, no 

 doubt, been melted in the crucible, and selected for the purposes of ex- 

 periment. 



Abstract of the Experiments on the Heaton Steel. 



This steel being the product of a totally different process of manufacture 

 from that of aU the other steel bars previously experimented vipou, and as 

 those bars were derived from the best known processes and received from 

 the best of makers, it is a matter of the greater moment to ascertain how it 

 stands ia relation to them as regards strength and those other properties which 

 are pecuKar to steel. It is for this object that an abstract separate fi-om that 

 of the Barrow steel manufacture has been drawn up. 



These bars, in their resistance to a transverse strain, show a very decided 

 superiority over the steel bars which I experimented upon before, and on 



