THE ROYAL ARTILLERY INSTITUTION. 
41S 
in density. Forging or drawing out the cast block imparts to it the desirable 
properties of great solidity and density. 
The cylinder is manufactured thus :—A large quantity of puddled steel 
having been broken up, the pieces whose fine fracture indicates a mild 
nature, are placed with a little flux in a number of plumbago crucibles 
containing about 45 lbs. each. An ingot for a 9-inch gun weighs 86 cwt., 
so 212 crucibles are required; these are placed in holes in the floor, under¬ 
neath which are air furnaces. The metal is melted in about three hours. 
The crucibles are then lifted, one by one, from the furnaces by means of 
tongs, and wheeled quickly to the mould; several men are employed in 
rolling up and pouring in the metal. They are obliged to keep up a 
continuous flow of molten metal, else the casting would not be homogeneous 
—hence the operation is at once important and resplendent; it lasts about 
twenty minutes. 
The mould is of cast-iron, and smeared inside with some non-conducting 
substance, a mixture of black lead generally. That for the 9-inch ingot is 
5 feet long and 2 feet square. The metal cools gradually, after which about 
Jth is cut off, and the lower end, being the denser, is marked for the 
breech. 
The block thus formed is drawn out by a series of heatings and hammer¬ 
ings which occupy several days, to a cylinder sufficiently long for an inner 
barrel, in which state it is sent to the Royal Gun Factories, where it is 
subjected to the following tests and treatment. 
A slice is cut off from the breech end and divided in pieces for testing. 
Some of these are flat bars, 4 inches long and J by § in section, and others 
are of the shape usually tested in the machine for tensile strength and 
elasticity. Three of the former are marked respectively S, L, and II One 
end of the S or soft (i.e. untempered) piece is gripped in a vice, whilst the 
other end is hammered down towards it, to ascertain that the steel, by 
bearing this bending without cracking, is naturally of the mild quality 
required. The L and H pieces are raised to a low red, and high heat 
respectively, immersed in oil, and, when cold, treated in a similar manner. 
Whichever of these pieces bears the hammering best, determines the heat 
at which the whole tube is to be toughened. Should neither piece answer, 
others at intermediate temperatures are tried, and if all fail, the block is 
returned to the contractors; but some specimen having succeeded, as is 
generally the case, two of the remaining pieces—one in its soft state, and 
the other toughened at the ascertained temperature—are tested for tensile 
strength and elasticity. The soft material should begin to stretch per¬ 
manently at 13 tons per square inch, and break at 31 tons. The toughened 
piece should begin to stretch at 31 tons, and break about 50. The permanent 
elongation is also taken, but it is not considered necessary to lay down any 
limits in this respect.* 
* It may seem remarkable that the colour at which a razor, a chisel, or a watch-spring must be 
tempered is definitely fixed, and yet that the heat for toughening a gun-barrel should vary in shade 
from a blood-red to a bright cerise. Now, did the temperature depend alone on the amount of 
carbon in the steel, it would appear best to toughen every barrel at a bright heat, for the less car¬ 
bonized, or in other words the milder the steel, the higher is the temperature at which it toughens 
[VOL. VI.] 54 
