274 WILLIAM FIELD HOW. 
Records of bending tests are, however, never so reliable as those 
made by an accurate tensile testing machine, where the treatment 
of the prepared samples cannot be varied as they may be by the 
different operators when the bending experiments are carried out. | 
Preparation of Test Specimens. 
Care is required in the preparation of specimens for testing 
purposes, and particular attention is given to the selection of 
samples from plates, bars, &c., to see that they are free from flaws. 
The selected pieces are then cut out by a parting tool, or, if 
more convenient, punched out, and the punched portions planed 
off about one quarter of an inch beyond the edge of the punched 
holes. This is especially necessary in dealing with steel plates. 
The samples should not be sheared from the plates, as it invari-- 
ably distorts the pieces and makes it necessary to straighten them 
before they can be tested; and although this straightening is of 
little moment in the case of bending tests, it is not advisable in 
any case to distort the material to be tested, by hammering it 
before the experiments cominence.. 
Specimens for tensile testing are most carefully prepared. The 
edges are usually milled, and when finished, no roughness is per- 
mitted to provide starting points for fractures. This is particularly 
avoided in the case of experiments with steel. The points between 
which the elongations are to be taken are of a very light character. 
When deep centre punch marks-are made in specimens of steel, 
they really constitute flaws. Not only should deep marks not be 
made in specimens for testing purposes, but brands of only the 
very lightest description should be made upon finished steel articles 
such as tyres, axles, &c. 
As the experiments are to ascertain the qualities of the steel 
proposed to be used in a structure, it should be tested exactly as 
it is cut from the material, and in the case of plates, flat bars, &., 
no planing of the surfaces or annealing is permitted. If the pieces 
are annealed the character of the material is altered, the tensile 
