THE KOYAL AllTILLEKY INSTITUTION. 
257 
safety of every rifled gun we have in the service, he it big or little; 
for, assuredly,, a construction which is not capable of firing with safety 
charges of two or three pounds of powder, cannot for one moment be 
trusted to fire charges of 100 and 120 lbs. 
2. The next point to be considered is the relative merit of steel 
and bronze as materials for the inner barrel of a gun, i.e. the capa¬ 
bilities of each to resist the wear caused by continued firing. It is 
not necessary to enter at length into this question. The staunchest 
advocates of bronze allow that it is deficient in hardness, the first 
quality which is required to resist the scoring action, due partly to the 
friction of the shot when passing through the bore, and still more to 
the heat of the combustion of the charge, and the rush of the gas over 
the shot. 
Again, it is found practically impossible to produce wholesale per¬ 
fectly homogeneous bronze castings, that is castings in which the 
quality of the metal is the same throughout, and which are quite free 
from tin-spots and porous patches. Mr. Abel, the Chemist to the War 
Department, in a minute dated August 28, 1869, accounts for this in 
the following way. He says :— 
“ The difficulty attending the production of thoroughly sound and sufficiently 
uniform bronze castings arises out of the circumstance that a mixture of copper 
and tin, which is sufficiently soft to constitute a material for ordnance, does not 
consist simply of one definite alloy of copper and tin; and that, when these 
metals are melted together, there exists a great tendency to the formation of alloys 
of definite composition in which the proportion of tin is comparatively high, and 
which, from their tendency to separate from the liquid mixture in a crystalline 
form, give rise to the production of cavities or porous patches in the castings, 
on the one hand, and of spots or veins of comparatively hard metal on the 
other.” .... 
Now these porous patches may occur in the interior of the mass 
where they are of little consequence, or they may occur in the surface 
of the bore, in which case they are even more important than those 
defects which, as already stated, have led to the abandonment of 
wrought-iron for the inner barrel of guns, inasmuch as tin is much more 
fusible than iron, and is consequently more rapidly acted on by the 
heated gases. None of us, I think, have the slightest conception of 
the enormous heat generated by the combustion of even comparatively 
small charges of powder, but some idea can be formed of it from con¬ 
sideration of the following fact. If a 12-pr. B.L. gun be fired for 
fifty rounds very rapidly, say in ten minutes, it will be so much heated 
that the hand cannot be placed on the outside. Now the total time 
that the heated gas has been in contact with the bore of the gun 
amounts in fifty rounds to only \ of a second, as the time for each 
round is Joth °f a second. Therefore the gun has been cooling in the 
intervals between the rounds for 9 minutes 59 § seconds and heating for 
i second, and still at the end of the series water will almost boil in it ; 
it is needless to remark that the heat even of an oxyhydrogen blow¬ 
pipe would be quite incapable of producing this result. Now the local 
heating at the seat of the shot is far greater in a rifled than in a S.B. 
