on Steam-Boats. , ; 63 
féason, the man-hole door to a cast-iron boiler is contrived to 
be on the inside; it does not depend upon bolts at all as they 
are constructed with us, it bears against the side of the boiler. 
Would it not be equally easy to afix man-holes so constructed 
to wrought-iron boilers?—There is no difficulty in doing it, 
either one way or the other. 
Supposing a cast-iron boiler and a wrought-iron boiler to be 
exploded by having too great a pressure applied, from which of 
the explesions should you apprehend the greatest danger ?—I 
think the danger is equal from one as the other. 
In what manner do you apprehend then, that a cast-iron boiler 
would explode ?—Probaby there might be some parts of the 
cast-iron boiler separate; and the wrought-iron boiler would 
probably rend. 
Should you not then apprehend a greater danger from the ex- 
plosion of a boiler which burst into fragments, than from ene 
which only rent ?—In every boiler that is built, there is one part 
of it weaker than another, and it is hardly possible for a boiler 
to be thrown about in fragments to do mischief. [ should not 
fee] any hesitation to sit on the cast-iron boilers I have seen in 
Cornwall when an explosion took place; I am convinced the 
explosion would take place at the under part. 
Do you think it necessary or advantageous that those boilers 
should be proved at their first erection, and that that proof 
should afterwards be repeated at intervals ?—It is certainly de~ 
sirable it should be done at the first erection; they ought always 
to be proved; the cast-iron boilers which have come under my 
notice in Cornwall, f calculate to be sufficient to resist at least 
thirteen times the pressure of steam we have ever used in them. 
To what heat are those boilers usually proved ?>—We work in 
general forty pounds to an inch in the high pressure boilers, and 
we prove them sometimes as high as three hundred, 
By a proof of this nature, so much within the supposed capa- 
city of resistance of a boiler, yon do not apprehend that any risk 
is incurred of injuring it?—Certainly not. 
And you yet conceive, that the proof is so far beyond the or- 
dinary resistance which is required from the boiler, as that there 
is no danger whatever of its bursting with a pressure of forty or 
fifty pounds an inch, when it has been proved by a pressure of 
three hundred ?—Certainly not. 
‘Do you apprehend, that it is perfectly easy so to construct 
and to secure your safety-valves, as that no engine-man, how- 
ever careless; shall be able to raise the steam beyond the pres- 
sure of forty or fifty pounds per inch ?>—There certainly is not the 
least difficulty in it. He 
You apprehend then, that with a boiler so constructed, so 
proved, 
