254 Report of the Select Commitiee 
the same plan, may be made equally strong, having the outside 
of cast iron and the inner part of wrought iron, would do the 
same thing. sl 
Do you, from your own experience, believe it possible to con- 
struct boilers which will bear an expansive force of 600 pounds 
to an inch ?-Yes; according to my experience, I have taken a 
good deal of pains to ascertain the strength of wrought-iron 
plate, and according to that I have made wrought-iron boilers 
that would bear 600 pounds upon an inch. 
What degree of pressure have such boilers generally been 
worked with ?—Such boilers have been worked from forty to fifty 
pounds upon an inch, and previously to being worked at all they 
have been tried with 150 pounds to an inch, by water pressure. 
Are you then of opinion: that there is no difficulty in con- 
structing the high pressure boiler of wrought iron, in such a 
manner as to make ft perfectly safe >—Yes, ] am of that opinion, 
that the boiler may be constructed of wrought iron, with perfect 
safety, at a pressure of fifty pounds. 
After the boiler is properly constructed, do vou apply any 
“further safeguards to it ?—We adopt two safety-valves, one in 
an iron box under lock and key, and that is only at the control 
of the proprietor, and the other is open to the engine-man; and 
we also employ a mercurial gauge as an inverted siphon, which 
in the event of the steam being stronger than the mercury ean 
sustain, the mercury will be driven ont, and the boiler thereby 
relieve itself. 
Do you consider this mercurial gauge in any other light than 
as an additional safety-valve, or as a contrivance by which no- 
tice is given of the pressure growing too high ?—In both these 
respects I employ it ; I consider that in both those two points 
of view it is useful. . 
Are you of opinion, that if the commun safety-valves be pro- 
pérly adapted, the mercurial gauge may be dispensed with ; when 
I say properly adapted, | mean sufficient in number and capacity, 
and one of them completely secured from the intermeddling of 
the engine-man?—I should think it would be safe. 
What do vou think respecting the comparative mischief pro- 
bably to arise from the bursting of a high pressure or a low pres- 
sure boiler?—In the high pressure boiler the injury would be 
done principally by the fragments projected ; in the low pressure 
boiler, the mischie! may arise chiefly from the hot water and 
steam. I may mention two instances in illustration of this ; the 
first, of a low pressure boiler having given way in the bottom, 
when a streain of hot water was projected against the engine- 
man, causing his death; the second instance was of a high pres- 
sure boiler, in which a hole was suddenly opened, the water aie 
jecte 
