54 
Duke of Wellington and many other eminent men, who took 
much interest in them. 
The non-adoption of his system arose from several radical 
defects in it — first, the danger from fire of having such a 
cumbrous furnace on a ship ; second, the time required to 
get up the steam in case of sudden encounter with an enemy, 
which might lead to a surrender before a shot could be thrown 
from the steam battery ; third, by unequal heating the tubes 
sometimes gave way, allowing the water to escape, and 
though the quantity being small would not cause explosions, 
leaks would deaden the fire and stop the action of the guns, 
and any suspension in the midst of action must be fatal to the 
ship using such a weapon. Still the after interest attached 
to the plan of the tubular boilers came from reversing the 
scheme used by Perkins, viz employing the tubes as flues 
for the fire, to convey the heat through the tubes to the water 
surrounding, then, in an outer boiler, by this method, without 
damaging the tubes, it is found that high pressure steam can 
be employed with safety and advantage, so that Mr. Perkins’ 
invention was not barren to the outer world, since his tubular 
boilers led to their extended employment in railway and steam- 
boat engines, and were, I believe, first employed by Stephenson 
a few years after the steam gun experiments had been put 
“ hors de combat.” 
NOTE. 
Although it is needless to describe the process of case hardening, so 
generally known, it may be well to explain that of decarbonising the steel 
plates for engraving. This process is as follows : — The prepared steel plates 
are placed in a cast-iron box, and covered about an inch deep with an oxide 
of iron, prepared by subjecting iron filings to alternate wetting and drying 
until they are mostly converted into red oxide. Over this covering a clay 
luting is placed so as to exclude the air, and the box is then placed in a 
furnace and kept at a red heat for about sixty hours, when the oxide in 
contact with the steel will have taken up the carbon from its surface to the 
depth of about a sixteenth of an inch, and thus convert the surface into" 
pure iron, as mentioned in the text. 
