MILD STEEL. 49 



mediate between these limits lie steels of various tempers, 

 that for bridge- bail cling having from 0"30 % to 0'3o % of car- 

 bon, with an ultimate tenacity of from 27 to 31 tons, with 

 30 % contraction of fractured area, and that for rails and 

 tyres having from 40 % to O'oO % of carbon. Beyond this 

 temper lie the different cast steels which are beyond the 

 scope of this paper. 



It is very desirable that the material should not contain 

 a greater percentage of carbon than that stated above. An 

 excess of carbon has the effect of rendering the steel capable 

 of taking a temper, which property'-, whilst tending to in- 

 crease its tenacity, also renders the material less ductile or 

 elastic ; and as the steel during its application might be 

 subject to such conditions as would cause it to take a temper 

 and so alter its properties, it is imperative that the per- 

 centage of carbon should be kept within such limits as will 

 preclude any possibility of this tempering taking place. 



I have already alluded to the universal practice of ex- 

 haustively testing this material, a practice I believe which 

 is the very essence of the success attending the use of " mild 

 steel," securing as it does most reliable data for determining 

 the proportions necessary to secure safety with economy of 

 material, or, commercially speaking, getting the most value 

 for one's money. 



To Mr. David Kirkcaldy we are indebted for very exhaus- 

 tive tables of the results of tests of almost every conceivable 

 description, on plates, plain, punched, drilled, and rivetted 

 joints, bars of all descriptions, rivets, plain and corrugated 

 furnaces, boxes representing combustion chambers of boilers, 

 and a host of other forms, conducted by him at the instance 

 principally of the Admiralty, the Board of Trade, the 

 Committee of Lloyd's Begister, and most of the large firms 

 of steel makers and steel users in this and other countries. 



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