282 WILLIAM FIELD HOW. 
In dealing with large forgings, such as crank and propeller 
shafts, the plan now adopted in the largest English works is to 
use hydraulic squeezers, which takes the place of the hammer and 
treats the metal in a more satisfactory mamner. The effect of 
blows from a hammer upon a mass of metal such as a shaft, is felt 
principally upon the outer surface, and this is shown by the ends. 
of the shaft so forged being concave; but when such a shaft is 
forged by the hydraulic squeezers the effect is felt throughout the 
- whole mass, including the portion at the axis which is forced out- 
wards, and the ends of a shaft so forged are convex. 
The treatment of rolled steel by fire is avoided as much as 
possible, and angles, channels, tie bars, &c. for bridge and roof 
work, are cut to the required lengths by cold saws. When it is. 
necessary to weld and forge, the portions so treated are heated 
and allowed to cool gradually after the operation, otherwise, initial 
stresses might be set up in the metal and cause fractures. Many 
cases of failure of forged mild steel plates and steel forgings have 
occurred which seemed inexplicable at the time, but were ultimately 
traced to the worked pieces not having been carefully and uniformly 
annealed, after portions had been treated in the smithy. 
With iron, the treatment by fire is not so injurious; but the: 
appearance of a structure is improved if the ends of the bars are. 
cut off by a cold saw instead of by a smith, and it is frequently 
found that smithing in such cases is more costly, as bars are 
occasionally split and spoilt when cutting them by fire, and this is. 
especially the case when the material is ‘‘red short.” 
. Rivetting. 
Where possible, rivets are now put in by machines, in prefer-. 
ence to the older practice of hand rivetting. In nearly all cases. 
the latter have the best appearance, but they are not so effective, 
as they do not completely fill the holes. There are, however, many 
boiler makers who maintain that they can make tighter work by 
punching holes in the plates—arranging the larger ends of the 
holes outwards—and rivetting by hand ; but as most engineers now 
