on Sleam-Boats. 97. 
and when they are hammered to secure the joint, they get cold, 
of course they shrink, and do not fill the hole through which they 
have passed. 
The wrought-iron boiler which vou stated burst was not ap- 
plied to a boat ?—No, for a salt-work. 
_ Is it your opinion, as an engineer, that any boiler, whether of 
wrought or of cast iron, but particularly of wrought iron, could 
be made, by the construction of safety-valves, so secure that all. 
danger from it would be almost impossible ?—At present I have 
no conception that any safety-valves could be applied to render 
them perfectly secure under heavy pressure. 
Is it your opinion, that if a boiler was originally constructed 
of wrought iron, to bear a pressure of 100 pounds to the square 
inch, and that such boiler had been tried by experiments, say at 
sixty, and that a safety-valve was applied to it which should open 
at a pressure of thirty, such a boiler would be liable to be ex- 
ploded ?—Not unless it had been previously strained by the ex- 
periment to render it too weak. 
Cannot a safety-valve be so made that it shall open, and be 
certain to open, at a particular pressure?—The safety-valves 
ought always to open at that pressure ; but from causes that we 
cannot ascertain, that does not happen in cases where accidents 
occur; it is to be hoped that safety-valves will be contrived to 
answer for high pressure engines. 
Would it not be possible to apply to such an engine as that a 
tube with a column of mercury?—Yes, and it would be a judi- 
cious application ; but it requires such an altitude, I apprehend 
it is not very easily applicable to boats from the agitation of the 
vessel; but if it could be applied, it is the best application thas 
can be made. 
In the low pressure engines the general safety is by a column 
of water ?—Yes. 
That could not be used on board a boat ?—No. 
Then you think the mercurial gauge would be the greatest 
safety for a boat, if it could be applied ?—Certainly; if it could 
be judiciously applied, it possesses greater safety than any other, 
Have you seen steam-boats on the Clyde or Humber ?—No, 
You know those on the Thames ?—Yes. 
What is the greatest power that would be required >~—The 
coudensing-engines should not be more than four pounds to an 
inch ; and if the capacity of the vessel allows of it, the condens- 
ing-engines answer every purpose, because you can have one on 
board more than sufficient for the tonnage ; because the making 
a wrought-iron boiler would be on such a Scale of thickness, 
that if more than the usual pressure was applied, the rivets would 
fail, and constitute a security against any fatal occurrence. 
~ Vol. 50, No,232, August 1817. G Could 
