on Steam-Boats. : 169 
liberty to be raised at the pleasure of the manager, because some- 
times it is expedient to raise it; the other should be under a 
cover of such description as not to be opened at all, at the dis- 
cretion of the engineer, but with sufficient apertures for the 
emission of the steam, and for any of the passengers to see that 
the valve is not made fast. It is also requisite that there should be 
a mercurial gauge of not less than an inch in diameter, and whose 
longest limb shall not be greater than two inches and'one-eighth 
for every pound per inch upon the safety-valve ; it is necessary, 
by occasional inspection, to take care that the mereury does not 
stiffen by oxidation, occasioned by the heat and motion to which 
it is in a slight degree liable. 
Do you conceive that a high pressure engine thus guarded 
might be used on board a steam-boat with safety to the passen- 
gers ?—Yes, so long as the boiler is kept in order ; but the boiler’s 
bottom is liable to erode or consume by the action of the fire, 
and therefore requires watching. 
How long do you think a boiler would last under the action 
of fire ?>—A boiler may last twelve months safely, provided its 
bottom be made of charcoal iron, beat not rolled, because there 
is a great deal of difference in the grain. 
~ Would you not always recommend a boiler to be made of 
wrought metal on board steam-boats ?—On board steam-boats 
I would recommend them all to be made either of copper or 
charcoal iron plates beat under the hammer and not rolled; the 
resistance of cylindric boilers will be in the inverse ratio of their 
diameters. 
[Mr. William Chapman was again called in on a future day, at 
his own request, and stated, that when he was asked as to loco- 
motive engines, he omitted to say that the diameter of their 
boiler was in general four feet, little more or less; that many of 
them are formed of cast iron, and several of malleable iron, and 
that the ends of several of these latter are of cast iron curved 
outwards; that in no one of them does the fire act upon the ex- 
ternal part of the boiler, but is placed in a malleable iron tube 
which passes through the boiler; a cast-iron boiler, however, 
being found far too heavy, the new loco-motive engines are al- 
ways supplied with malleable iron boilers. } 
Mr. Puitie Taytor’s Evidence. 
Will you be so good as to state what is your occupation ?—A 
manufacturing chemist. 
Where do you reside ?>—~At Bromley in Middlesex. 
You are conversant with the nature of steam-engines ?—My 
attention has been directed to the use of steam from a desire to 
, apply 
