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Review of Renwick 
er safety depends on human vigilance, it will sometimes be jeopar- 
dized ; for that vigilance will sometimes slumber. — 
“Bat notwithstanding the dangers inseparable from so powerfal an 
agent as steam, yet in fact but few of the explosions of the steam en- 
gine which have ever taken place are attributable caer to the ener- 
gies‘of the moving force. 
In all cases, where fatal accidents have occurred, the explosion ap* 
pears to have been due to other causes than ‘the mere expansive force 
of the-steam that would be formed when the boiler is in proper order, 
and seyenet: woh water.—p. 97. 
_ This, however, it must be acknowledged, is only saying, that ae 
ing necd prehended from the energies of the movines orce 
oa 2 
‘ment of powerful agents always more or less dangerous. 
would seem at first view a very easy matter to sri against 
It 
% danger from the active energies of steam, by the means of safely 
These, however, sometimes, either by accident or design, 
Reronie too heavily loaded ; they are also liable to lose their sensi- 
bility by becoming rusty, and in various other ways; and such vast 
quantities’ of steam are sometimes suddenly generated, that the safety 
valves are inadequate to afford any relief. Our author strongly 1e- 
commends that every boiler should be furnished with two safety 
valves, one of which should not be under the control of the fireman. 
Tt would also appear to be within our ‘power to provide against 
hazard from the expansive force of steam by proving the boilers; 
that is, by previously subjecting them to a pressure much g ereater 
than that under which. they are intended to work. 
+ dt has been proposed to apply a pressure five or six times as great a a 
the boiler is intended to bear. Nor is this too great a precaution, for the 
water proof is. ‘performed when cold, and the > ractal i is then more tena 
cious than when heated, and the pr eportion of six to.one, at least, is 
necessary before this difference is obviated. If a boiler be not sub- 
jected to such proof, it may be possible that when nee its limit of 
rupture may be reached before the safety valye open The water 
proof having been performed, the boiler.should next bd subjected to. 
a similar trial by steam, say of twice the force that is usually to - 
generated in the boiler without causing its safety valves to act, | : 
France, it is required by law, that all high pressure boilers be subject 
ed toa proof five times as great ; as Pe boiler is intended to bear whe 
in service.—p. 85. . - te 
