THE ROYAL ARTILLERY INSTITUTION. 
129 
taken out, the head is cooled by the chill to a dark colour, while the body is 
still red. The upper box is removed, the spindle withdrawn, and the runner 
and riser cut off the shell with a broad chisel; the shell is removed from 
the lower box, and wheeled off to a pit partly filled with dry sand, where it 
is covered over for 14 or 18 hours.* 
The object of casting the head down is to obtain as sound a head as 
possible. 
The foreman is enabled to judge how the work is turning out by in¬ 
specting the fracture of any defective castings, which are broken up under a 
steam hammer; the weight of the projectile is also an indication of the 
quality of the iron, as the shell would run light if a soft or not dense enough 
metal was employed. 
The difference between the metal body cast in sand and the head is very 
marked in a fractured shell; the body having a well-defined mottle, while 
the head is a bright white. The effect of the chill extends some way into 
the body. It is important to remark that the head is not touched by any 
tool after leaving the chill; if the skin was removed, the strength of the 
head would be reduced. It is a well-known fact that the strength of a 
casting is materially reduced by turning off the outer skin, which is always 
the soundest and densest part of the casting, the quick cooling preventing 
the formation of large crystals. 
When the shell are sufficiently cool the core is scraped out, and while 
still hot the shell is lacquered. It is not desirable to heat these shell by 
steam, like common shell, as they may be injured by change of temperature. 
They are next tested by water pressure, 100 lbs. to the square inch, and the 
bases are carefully hammered all over with sharp-pointed hammers to detect 
flaws. The body is then ground down to the final dimensions on a revolving 
grindstone, as the metal is too hard to be turned in the ordinary w r ay. The 
shell is placed in a lathe, and the cast-iron ring in the base tapped to receive 
the plug. The studs are pressed in, turned and planed, the lead ring sealing 
the junction of the cast-iron bush and the body is hammered in, the studs 
trimmed by hand, and the base-plug—which is not interchangeable—care¬ 
fully fitted to each shell. The plugs are smeared with equal parts of cocoa- 
nut oil and ground chalk. The plugs are made long to fill up the recess, 
to avoid any risk when the powder sets back. 
Finally, the shell are gauged and examined. The limits over the body 
are ±*015 in. instead of ±'01 in., as in common shell. The following 
gauges are usedHigh and low ring, over body, do. over studs, cylinder 
gauge. 
On the base of the projectile will be found u Palliser shot,”—or “ shell,” 
as the case may be—also the calibre of the gun, and if 12-in. the weight of 
the gun will also be given. The month and day of casting will also be 
found on the base, and also two letters indicating the iron used in casting, if 
cast prior to November 1874. The month and year will be found on one 
of the studs ; also a x, to show that the studs are planed to fit the grooves. 
The E, which indicated that the projectile had been examined, was discon¬ 
tinued in 1873. All shells of that and later date may be considered as 
having been examined and tested as above. 
This is important, as it is essential that the shell should cool slowly, otherwise it will be brittle. 
