ii 3 bs 
268 ‘WILLIAM FIELD HOW. 
square inch and elongation, and also the reduction of area, as this 
only creates indecision in the minds of the inspecting officers. 
For instance, if any particular metal will withstand the required 
number of tons per square inch, and elongate the stipulated 
amount, it would be unwise to reject such iron or steel if it were 
not to give the required reduction of area. Yet this occasionally 
has to be done if the inspecting officer is not at liberty to exercise 
his own judgment, or cannot readily communicate with his 
principals. 
In dealing with the results of tests, engineers usually take the 
whole of the results into consideration, before accepting or reject- 
ing iron or steel, and their decision is guided by the purpose for 
which the material is to be used. 
As an instance ; if it be specified that certain bridge iron shall 
withstand a stress without fracture of twenty-two tons per square 
inch, and elongate ten per cent. in ten inches, they would not 
hesitate to accept it if the tests showed that the specimens broke 
under a stress of 21:5 tons and elongated fifteen per cent. in the 
ten inches. Yet this iron, which is really of a more reliable 
character than that stipulated for, would have to be condemned 
if the specification were literally adhered to. 
The test of tyres is also a case in point. These portions of a 
wheel are usually required to stand being deflected by blows from 
a falling weight until they are bent one-sixth of their internal 
diameter, and pieces cut from them are required to have a tensile 
strength of from forty five to forty-eight tons per square inch, and 
elongate not less than ten per cent. in two inches. Now, if the 
tyre deflects the required amount, surely this is a sufficient 
guarantee of its ductility, and it is exceedingly hard upon manu- 
facturers to have numbers of such tyres rejected simply because 
the required elongation has not been recorded by the tensile test- 
ing machine. There are many other instances of daily occurrence 
where material has to be condemned which capable supervising 
