44 



Popular Science Monthly 



The red hot steel about to be plunged into 

 the oil tank for what is known as its "heat 

 treatment." The tank extends down into 

 the ground. The plunging of the hot steel 

 into the oil suddenly cools it and hardens it 

 and refines its grain or texture. After this 

 it must be heated up again to temper it 



must be strong and that its life is short! 



In the case of a "built-up" gun, as it is 

 called when made of hoops or bands of 

 steel, the outer tubes or rings are shrunk 

 or sweated on — that is, they are heated 

 so that they expand or swell a little, as all 

 steel does when heated, and then while 

 hot they are fitted over the inner part 

 and allowed to cool and shrink, or contract. 

 In so doing they fit very tightly on to the 

 main tube. In making a wire-wound gun, 

 the wire is wound or coiled around and 

 around until more than one hundred miles 

 of it has been wrapped around the big 

 cannon. A 12-inch gun requires 117 miles 

 of wire weighing about thirteen and one- 

 half tons. Although the strength of the 

 wire is such that it gives great resisting 

 force to pressures exerted sideways, it does 

 not bestow strength lengthwise. Therefore 

 an extra thickness of metal must be put 

 on the muzzle of the gun where the vibra- 

 tion caused by the shell leaving the gun 

 is the greatest. 



The breech or back end of a gun is a 

 very important part. Here the shell is 

 inserted in a specially built chamber. 

 After the shell is in place, the breech is 

 closed by the shutting of a very complicated 

 and strong door. It is fastened or fitted 

 in the gun by extremely strong screws so 

 that the charge will not burst the gun 

 open at the back when it is fired. 



Sometimes a shell explodes in the barrel 

 of the gun. In a wire-wound gun the 

 wire tends to prevent a grave disaster; it 

 hinders the steel tubes from bursting into 

 many pieces and flying in every direction. 

 The solid gun is wholly built of tubes, 

 while in the wire-wound gun there may 

 be one or two tubes over which the wire 

 is wound with the jacket tubes shrunk 

 over the wire. A bush for the breech-ring 

 is screwed into the rear end, which is also 

 reinforced by a breech-ring outside. 



Heat Treatment and What It Means 



With all these precautions to make a 

 big gun strong enough to withstand pres- 

 sure, the result would not be successful 

 except for the extreme care in making the 

 steel and its "heat treatment." Steel in 

 its crude state, or when originally cooled 

 from its molten or liquid condition, is one 

 mass of crystals relatively large and in- 

 timately knit together. But when these 

 crystals are large the steel is not as strong 

 as when they are small and fine. The 

 object of heat treatment is to render all 



