200 
MINUTES OF PROCEEDINGS OF 
force greater tlian tlie maximum powder pressure, to which it can at any 
time be subjected.* 
Chilled bronze he found had an elastic limit of 2\ tons, with an 
elongation of 0.0004, while if the same metal had already undergone 
a permanent extension of ten times the latter amount, or 0,004, its new 
limit of elasticity became 10 tons, and it was capable of an elastic 
elongation of 0,00192. 
As the calibre fixed upon for the new Austrian field piece is 87 m. m., 
it would, according to this experience be sufficient to expand the bore 
by four thousandths, i.e. —87 m - m * x by 0.004 or about 0.348 m - in order 
to obtain a new limit and to quadruple the elastic strength of the gun. 
To give this necessary expansion to the bore, conical mandrils of 
hardened steel, were driven through an ingot of bronze steel, cast hollow 
in chill, in the manner already explained. 
Hydraulic pressure of about 15 tons to the square inch was employed 
for this purpose, and several mandrils increasing slightly in size were 
successively forced through the bore until it was increased from 80 m * m - 
in diameter to 87 m * an increase of 8.75 per cent.f During this 
operation the exterior of the ingot was also increased in diameter by 
about 2 per cent. At the close of the operation, the bore presented a 
surface polished like a mirror, and with a hardness equal to that of steel. 
When the last mandril had been passed through, the elastic contrac¬ 
tion of the bore was found to be 0.004 of its diameter, an important 
fact which, according to General d^Uchatius, showed that e< all the 
concentric layers of the piece, were in a state of elastic tension, exerting 
from the exterior towards the interior, a pressure equal to that which 
the mandril exerted from the interior towards the exterior, the latter 
being at least 14.75 foot tons, as far as could be calculated.^ 
As a proof that this tension extended even to the exterior layers; 
a very thin ring of metal was turned off the outside of a cylinder treated 
as above, and before the last element of this ring had been cut through, 
the ring sprang off the cylinder and its diameter immediately became 
smaller than that of the latter; a similar ring cut from the interior, 
dilated on the other hand, when the separation was complete, showing 
that the metal there was in a state of compression. J 
# ' By this General Yon Uchatius would appear to mean that any permanent expansion 
of the bore by firing, and so increased windage and bad shooting, should be prevented by 
previous mechanical treatment of a material otherwise too soft. It is a question whether 
extra strength is given to the inner layers by this treatment, or whether a part of their 
total tensile strength is not overcome (vide note II.) they become denser, however, and so 
stronger to resist abrasion, while the elastic limit is higher. 
f Sir J. Whitworth compresses his steel with a pressure of as much as 20 tons per square 
inch, reducing the length of the ingot by about one-eighth. 
J This is quite clear, nor can there be a doubt that as General Yon Uchatius states “ the 
successive strata of metal in the steel bronze gun, from within outwards, possess a relative 
diminishing strength, hardness and elasticity, which is precisely what is demanded by the 
objective; at the bore namely the metal is strongest, hardest and most elastic (i.e. does 
not stretch most, but requires the greater force to stretch it to its elastic limit,) and as 
these properties diminish the toughness (ductility) of the metal decreases.” 
Is this gain brought about, however, by a loss in the total strength of the cylinder against 
rupture from within P 
The German critic, quoted in note II, says that it is so, that General Yon Uchatius is 
working upon a false conception of the laws of elasticity and strength, and that technical 
science will never admit that it is preferable to employ an overstrained to a sound material. 
