THE ROYAL ARTILLERY INSTITUTION. 
201 
When a piece made as described is fired, the bore will, according 
to General Yon Uchatins, undergo a sudden expansion; and immedi¬ 
ately return to its original dimensions, provided this expansion does 
not exceed ^ of its diameter, as a spring rebounds unless stretched 
beyond its endurance. Should the tension of the gas be so great as to 
cause a greater dilatation of the bore than tuoo of its diameter, then 
the elasticity of the metal being exceeded, the bore would become 
permanently expanded. Such permanent expansion could only take 
place if the pressure produced on explosion surpassed that which the 
mandril driven through it exerted on the walls of the bore during 
manufacture; i.e. } the pressure of the powder gas must be more than 
14* * * § 75 tons per square inch, a pressure not likely to occur in field guns. 
General Yon TJchatius therefore considered that a gun made of steel 
bronze, as proposed, would be capable of fulfilling the conditions 
required of a field gun— i.e., that it would be able with the normal 
charge to stand a great number of rounds, without any detriment to its 
accuracy; and further, that if it should, by accident, be submitted to a 
very excessive strain, it would not burst explosively, on account of the 
extreme ductility of the outer layers. 
He states the following as some of the advantages of such pieces :— 
That they would compare well with those made of steel in the 
ordinary way,* having the same hardness and homogeneity, and being 
submitted in manufacture to a greater pressure from within that which 
the powder gas can exercise. 
In guns made of bronze steel, the properties of the metal in the several 
concentric layers differ in such a manner that while hardness, density, 
elasticity,! and tensile strength diminish from the interior to the 
exterior, the ductility of the metal (measured by the amount by which 
it will elongate prior to fracture) increases, and is at a maximum at the 
exterior surface. J 
In these pieces every concentric layer of metal performs its proper 
amount of work, and gives its proportional support to the walls of the 
bore, the “ neutral ” layer, or that layer in which equilibrium exists 
between the compression of the inner portions and the tension of the 
outer, is close to the surface of the bore, instead of being near the 
exterior of the steel barrel, as in built-up guns.§ 
* Probably steel might be treated in a similar manner, and improve also in the 
properties mentioned as shown by Table B, the result of other experiments, by Gen. 
Yon Uchatins. 
f That is to say its “ limit of elasticity ” as defined by us, and measured by the greatest 
statical pressure which can be applied to a bar of a square inch section without producing 
permanent change of form. This is the same limit defined by Colonel Rosset, and rather 
more truly, as the “ limit of cohesion,” or that limit at which permanent change of form 
rapidly and definitely takes place, for long before that limit a small and gradual permanent 
deformation will have been caused. 
f As will be seen by Table A the metal in the outer layer is 16 times as ductile as that 
of the inner layer. The ductility of good wrought iron of 27 tons tensile strength has 
been found to allow of an elongation of 038, while bronze steel from the exterior layer 
with 21 tons tensile strength shows a ductility of 040. 
§ We cannot allow that this is the case with our own guns, when we 3 ee that the steel 
tube is so much compressed in some cases by the shrinking on of the outer portions, that 
the diameter of its bore is sensibly diminished. 
