MILD STEEL. 53 



from surface condensers does not affect it to the same 

 extent. My theory is that the steel being the softer 

 material is more readily attacked by the mechanical action 

 of the steam bubbles and water leaks, and on the other 

 hand being of a more uniform character is not so readily 

 attacked by the condensed water, the surfaces remaining 

 smoother for a longer time, so that the scale and dirt does 

 not so easily adhere to them as it does to the rougher iron 

 plates. In constructions of iron and steel of equal strength 

 there is a savinsr of about 20 /^ in weig-ht in favour of the 

 steel, but owing to its greater elasticity its deflection under 

 a given load is considerably more than in the case of iron, 

 and where this excess of deflection is inconvenient or 

 dangerous it is necessary to provide additional sti:ffening. 

 I am of opinion that in a good many steel structures 

 ever}' advantage has been taken of the tenacity of the 

 material, and that the question of stiffness or resistance to 

 buckling has been overlooked or neglected altogether. The 

 advantage of mild steel over iron has perhaps been best 

 illustrated in connection wdth the shipbuilding industij-, 

 where on account of its superior tenacity the scantlings have 

 been reduced by 20 %, and its elasticit}' affords greater 

 security in the case of strandings, as the plates and framing- 

 will sustain a very considerable amount of bulging and 

 buckling before fracture. 



It is very doubtful whether or not the triple expansion 

 eno-Ine would have been the success it is without the 

 introduction of mild steel. In one "point only is it inferior 

 to iron. Although it is frequently welded, the welds are 

 unreliable, and are only employed in compression, and even 

 then are better if fitted with a covering plate. But this 

 defect being known can be guarded against, and any risk 

 compensated for. 



