50 



MILD STEEL. 



Tlie following table is very instructive as showing at a 

 glance the superiority of steel over iron plates. The ulti- 

 mate stress of the steel plates is about 36% greater than 

 the mean of the iron plates, and the contraction of area at 

 fracture Avhicli is a measure of the ductility largely exceeds 

 that of the various irons, being 49*1 % for the steel, against 

 20-6%, 13-07%, 5-4% for the iron plates respectively. It will 

 therefore at once be seen how this property renders " mild 

 steel " a much safer material to use than iron, especially in 

 structures where it may be subject to suddenly increased 

 strains, since the steel will by its extension and distortion 

 call attention to the fact of its being overstrained long 

 before the point of actual fracture has been reached. 

 Again, the ultimate stress and contraction of area at 

 fracture crosswise is considerably less than lengthways in 

 the iron plates ; this is not the case to so great an extent 

 Avith the steel plates, the ultimate stress of the steel in"both 

 directions being almost identical, and the ductility cross- 

 ways is not much less than lengthways. 



(Kirkcaldy.) 



