' TREATMENT OF MANUFACTURED IRON AND STEEL. 269 
officers know to be perfectly good and reliable, and suitable for 
the purpose intended. 
Where falling weight tests are not required, the elongation is, in 
the author’s opinion, the best criterion of the ductility of material, 
because the metal that has given a good extension generally shows 
that it must have stretched fairly over the whole length of the 
specimen before the “ yield” point was reached; whereas, a piece 
of an irregular character might have a soft place in it which would 
give a great reduction of area at the breaking point, but the other 
part of the bar might be hard. 
When tests are to be made from steel boiler plates the most 
strict specifications require six strips to be selected from the rolled 
steel before it is sheared to its required size, viz., three with and 
three across the leagth of the plate. Two of these, one with and 
the other across the length, are tested by tensile stresses, two by 
cold bending or some other experiment such as punching and 
drifting to ascertain the ductility, and the other two by bending 
cold after having been heated to a cherry red and quenched in 
water having a temperature of eighty-two degrees Fahr. Should 
the specimens so tested comply with the specification, the plate 
is accepted. 
This apparently large number of tests is insisted upon to pro- 
vide against the possibility of a brittle steel plate being used in 
the manufacture of a boiler, but from the material to be used for 
the manufacture of bridges, roofs, and work of that character, it 
is usual to test only a limited number of specimens taken from 
plates made from the same cast of metal. 
With regard to the specified tests for bridge plates ; the tensile 
specimens being cut from the plates and tested in the exact con- 
dition in which they are to be used, ensures the character of the 
metal being correctly ascertained as regards its ultimate strength 
and ductility. 
If all the strips were heated and quenched, and then tested, a 
plate that might have been worked when tao cold, viz., at a blue 
