PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 413 



enlarg-ing the diameter, by a pressure on small surfaces, until the density 

 of the metal is also affected in this part to half its thickness. The holes 

 left by the distance-cores are then, with the exception of one, stopped by 

 screw plugs EE, etc., after which the chamber is filled with melted lead 

 C. After the gun has cooled, a hydraulic or other press is attached to each 

 of the holes in succession, and additional lead, in this manner, is forced in, 

 to give the same amount of compression to the inner surface of thu 

 chamber as had been given before to the outer surface by hammering, or 

 until the outside shell is slightly expanded. By this means, most of the 

 compressibility of the bronze is taken up, and its elasticity much increased; 

 as, by hammering, a spring temper is imparted to the bronze, giving it the 

 elasticity of spring steel The lead also answers the purpose of a con- 

 ductor of pressure, from its incompressibility. 



The bore of the bronze A, to receive the steel lining B, is tapered, being 

 about one inch smaller at the breech than at the muzzle. The steel lining 

 is turned a very little larger than the bore, and with a corresponding taper, 

 and is also forced into its place by a hydraulic press. The bronze metal 

 about this steel linin.g has a strain of compression upon it from the pres- 

 sure of the lead, and a strain of compression also rests upon the steel 

 lining. Any pressure having a tendency to enlarge the diameter would 

 be resisted directly by the strength of the outer shell, as, when the gun is 

 completed, it is intended that nearly all the compressibility of the bronze 

 shall have been destroyed by the hammering and by the pressure of the 

 lead, as well as a great part of its elasticity, by forcing the steel lining 

 with great force into the tapered bore. The steel lining is to have only a 

 sufficient thickness to retard a part of the heat in the combustion of the 

 powder; so that the proper proportion of heat is communicated to the 

 bronze, and this proportion is regulated by the thickness of the steel lining. 

 A space is left in the bore of the cylinder A, and after the insertion of the 

 steel lining B, this space is also filled with lead D. By this means, careful 

 fitting of the steel B, to the bottom of the chamber in A, is made uimeces- 

 sary, and after the lining B, is forced in, against the shoulder at the muz- 

 zle end, a proper amount of pressure can be equally distributed about the 

 spherical end of the steel lining; and during the service of the gun, this 

 pressure can be corrected by the use of the screw d. The steel lining B, 

 is prevented from changing its position by any shock to the gun, by two 

 keys FF, inserted in such direction as to prevent withdrawal of the lining, 

 without first withdrawing the keys. They also prevent the lining from 

 revolving in the gun, by the pressure of the shot against the side of the 

 lands. 



Bronze is one of the best among the conductors of heat, transmitting it 

 with rapidity. The heat conductors A^ radiate from the center of the 

 sphere, and the bottom of the bore is continued beyond the center of the 

 sphere, so that the mean center of heating surface may be at the center of 

 the gun. 



The lead is a conductor of pressure, it being more nearly incompressible 

 than any other of the metals, which renders it eminently fit for this pur- 

 pose. 



The right hand side of the following figure is half of a front elevation; and 



