TREATMENT OF MANUFACTURED IRON AND STEEL. 275 
‘strength being reduced and the elongation increased. Consequently 
they would bend better than the plates from which they were cut, 
-and could not be a criterion of the material proposed to be used. 
For tensile tests it is usual to keep the sectional area of the 
sample as near a square inch as possible, but it is not advisable to 
‘test wide widths of thin plates &c., because the stress is seldom 
uniformly distributed over such specimens, and then fractures will 
‘first commence from one edge, unless special precautions be taken 
with the grips or other means employed to hold the sample. 
The usual method of fixing a specimen cut from a plate or bar 
‘an a tensile testing machine, is by means of two taper wedges 
provided with serrated teeth on the faces placed next to the 
_ specimen, and it is of great importance that these serrated wedg«s 
should be perfectly accurate and that the portions of the specimen 
they grip be quite parallel. Otherwise, a bending stress is thrown 
- upon the sample, one side of it will be strained to a greater extent 
than the other, and in such cases, it is natural to suppose that the 
fracture will first take place from the side subjected to the greater 
‘stress. Strips of plate to be subjected to bending tests, have the 
edges planed as previously mentioned, and the edges are carefully 
rounded at the corners. Ifthis removal of the angles is not carrie l 
out, cracking will commence at the sharp corners and rapidly 
extend across the pieces of plate, whereas the samples will bend 
through an angle of many more degrees if the edges are taken off. 
When in England, the author had brought before his notice 
‘some bending tests that were carried out upon a mild steel plute 
one and one-eighth inch thick. A specimen sheared from the 
plate broke like cast iron when bending was attempted, but a 
sample cut from the same plate bent in a most satisfactory manner 
after it had had its sheared edges planed off and the sharp corners 
rounded. 
With regard to the number of tests required, that is usually 
decided by the engineer. Ina light structure, composed of few 
bars and plates, the number would be limited, but in larger works 
