‘ 
on Steam- Boats. 91 
the plate of cast iron was of inadequate thickness for the strain 
to be put upon it. With respect to the impropriety of cast iron 
compared with wrought, we ourselves constructed one of the first 
high pressure boilers we used, precisely in the same manner with 
that on board the Norwich boat; the boiler was proved to 160 
pounds a square inch, by the water proof, commonly used with 
about forty pounds pressure, but the cast-iron end broke one day 
with less than twenty pounds pressure of steam; the fracture 
being caused evidently by the heat expanding the cast-iron end 
unequally, and being kept from going to the form it would 
otherwise assume. 
Then you are of opinion it would be improper to make one of 
such a construction ?—As far as J at present know, I should say 
it was. Upon that we altered our boilers, all having been since 
made of wrouglit iron only. I have seen most of the high pres- 
sure boilers which have been made, except Woolf’s. I have seen 
Trevethick’s old construction, which were cast iron; his new 
construction with his wrought-iron tubes. The Wells-street 
boiler, which blew up, I saw immediately after its destruction ; 
I was surprised to see that it had been made of cast iron, a pan 
of eight feet diameter therefore extending the bursting surface 
in the proportion of four to sixteen ; it was of unequal thickness, 
badly cast, cast from small furnaces, and the contact of the iron 
not complete ; it did not meet in fusion. 
Was that a high pressure boiler ?—Yes, intended to boil su- 
gar; the thickness was intended to be, doubtless, about two 
inches or two inches and a quarter, but by inserting the core 
unequally, the thickness on one side was three quarters of an inch, 
on the other side the thickness of the metal was two inches and 
a quarter, or thereabouts; therefore to the general objections to 
cast iron was added a most improper construction. I under- 
stand from the men who were working there (the Frenchmen) 
that there had been something like a mercurial gauge attached 
to it, but that the mercury never fluctuated; it indicated no- 
' thing that the safety-vaive was loaded down with weights, which 
we could not collect, and therefore did not ascertain the pres- 
sure; but that it was probable there was a pressure of more 
than 100 pounds per inch. 
Had you ever seen it worked before ?—No, nobody was ad- 
mitted to see it worked. 
How many accidents have occurred in the high pressure boiler 
to your knowledge ?—The first | ever heard of was one of Treve- 
thick’s at Woolwich. 
Was that a cast-iron boiler?—It was, In that case the safety- 
valve was a very awkward thing, hardly to be called a safety- 
valve; he himself was not awakened to the danger till that ac- 
cident 
