Still the same general characteristics were to be noted,
and it may be broadly stated, that England chose confessedly the weaker
material, as being more under control, cheaper, and safer to intrust
with the lives of men; while Prussia selected the stronger but less
manageable substance, in the hope of improving its uniformity, and
rendering it thoroughly trustworthy. The difference in strength, when
both are sound, is great. Roughly, gun steel is about twice as strong as
wrought iron.
I must now say a few words on the nature of the strains to which a piece
of ordnance is subjected when fired. Gunpowder is commonly termed an
explosive, but this hardly represents its qualities accurately. With a
true explosive, such as gun-cotton, nitro glycerine and its compounds,
detonation and conversion of the whole into gas are practically
instantaneous, whatever the size of the mass; while, with gunpowder,
only the exterior of the grain or lump burns and gives off gas, so that
the larger the grain the slower the combustion. The products consist of
liquids and gases. The gas, when cooled down to ordinary temperature,
occupies about 280 times the volume of the powder.
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