on Steam-Boats. 177 
fine, under «such circumstances using the expansive force to 
forty pounds to the inch, and not beyond forty pounds, would 
be a safe and efficient engine. 
Under all the circumstances which at present exist in the ma- 
nufacture and management of a condensing and high pressure 
engine, with a view to the safety of passengers in a steam-boat,. 
which of them would you recommend ?—-Under all the cireum-- 
stances of the case, I should most decidedly recommend a con- 
densing engine, a condensing engine with a wrought-iron boiler; 
because when cast iron becomes subject to high expansion and 
contraction, the constant repetition of these effects in a very 
great degree impairs the strength of the boiler. 
That mischief would not be incidental to a wrought-iron 
boiler ?—Certainly not. I should venture to say, that all en- 
gines itssteam-boats should be subject to regulation and inspec- 
tion by competent persons ;—a steam-boat must have a register, 
and before such register should be granted, the engine should be 
inspected, to see whether it is of a character to deserve its being 
considered safe. 
What is your opinion as to the expediency of adding a mer- 
curial gauge ?>—By no means do I consider it an efficient and 
convenient apparatus on board a boat ; it would be constantly in 
the way, and it would require a great column of mercury to make 
it safe; and that such a quantity may be liable to do mischief if 
blown out. A 
Has it ever happened to you, to form any calculation of the 
proportion which a mercurial gauge ought to bear to the dia- 
meter of a boiler?—I have not; but it will depend upon the 
expansive force to which the boiler is to be brought up, as well 
as to the capacity of the boiler; because, if you were to put a 
mercurial gauge to give merely the pressure on the boiler, that: 
would not be adequate to carry off the quantity of steam that 
may be generated in a mischievous way. 
What is your opinion as to the comparative consumption of 
coals in condensing and high pressure engines, with respect to 
the work produced ?—I am quite satisfied, that taking for granted 
that both engines were judiciously formed, the one would take 
as much fuel as the other, there would be no material saving, if 
any; but if you associate the two principles together, as in the 
case of Woolf’s engine, there will be a considerable saving ; unite 
the high pressure with a condensing engine, and there is a great 
saving, but in their abstract characters there is none. 
Mr. Joun Brairuwarre’s Evidence. ' 
What is your profession and place of abode ?—I reside in New 
Road, Fitzroy-square, and am an engine-maker and engineer.’ 
Vol, 50, No, 233, Sept, 1817. M The 
