276 WILLIAM FIELD HOW. 
where there are many similar members, a greater number of tests 
are made. It is not possible, in constructional work, to stipulate . 
the percentage of tests as is done in the case of tyres, axles, and 
such like details. 
Manufacture. 
Before the material is dispatched to the bridge yard, manu- 
facturers frequently arrange to have it inspected at the rolling 
mills by a reliable man who will carry out tests, and if it complies 
with the specification, he will carefully examine the plates &c, to 
see that they are free from flaws, that they have been carefully ~ 
and truly sheared, that their dimensions are correct, and that their 
weights do not exceed the permitted deviation, which is usually 
two and a-half per cent. above or below the calculated amounts. 
Payment is generally made upon these weights, unless some 
arrangements are made. 
The inspection to ascertain the weight of material is of impor- 
tance, because if the manufacturers are to be paid by weight and no 
estimated quantities are to be worked to, the plates are frequently 
rolled “ full,” the result being that the girders &c. made from them 
exceed the engineer’s estimates. This is anadvantagetothemanu- \ 
facturers if the actual weights are paid for, but a loss to them if 
only a small deviation from the estimated weights is permitted. 
The plates, with the results of the tests, are sent to the bridge 
manufacturer’s works, where other tests are usually required by 
the engineer to confirm those already recorded, and if the tests 
carried out at the rolling mills are confirmed, the manufacture of 
the work is allowed to proceed. 
Plates of large area are always slightly thicker at their centres 
than at their edges, owing to the bending of the rolls, and this is 
particularly noticed in thin plates where it is desirable to keep 
down the total weight of manufactured articles, such as gas 
holders for railway carriages, and at the same time ensure a 
maximum strength at the welded joints by keeping up the 
thickness of the edges. 
