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264 WILLIAM FIELD HOW. 
extent. The loss by rust of iron and steel being practically the 
same, the percentage of reduction of the effective strength of the 
thinner steel plates would be greater if that material were used. 
Good iron is more reliable than steel where much forging of the 
rolled material is required, and it is undoubtedly preferable to 
use it for details that have to be welded. Again, iron being 
structurally of a laminated character, it is but slightly injured by 
punching and shearing. 
Owing to the fibrous formation of wrought iron its strength 
across the length in which it has been rolled is generally consider- 
ably less than in the direction of the length of the plate, bar, &e., 
and care has to be taken that the rivets in long and compara- 
tively narrow details, such as the webs and tie bars of girders, 
are kept well from their edges and ends. 
The author has found from experiments that in iron work, 
where the ultimate tensile strength and elongation in the lengths 
of the web plates of iron girders have been twenty-two tons and 
twelve per cent. in ten inches respectively, specimens cut from 
such webs at an angle of forty-five degrees (that is, in the direc- 
tion in which the stresses from the tie bars act), possess a tensile 
strength of nineteen tons per square inch, and only 6°8 per cent. 
of elongation in a length of five inches. Such specimens have 
broken across in the direction in which the iron has been rolled. 
When the stress has been directly at right angles to the length 
of the plate, the ultimate tensile strength was only eighteen tons 
per square inch, and elongation four per cent. in five inches. 
Mitp STEEL. 
During recent years, so much progress has been made in the 
manufacture of mild steel, that it can now be produced having a 
tensile strength and ductility of surprising regularity, and owing 
to its uniformity in these respects and great tensile strength, it is 
being rapidly adopted by the most eminent we” for the 
construction of bridges, roofs, boilers, etc. 
