24 
MINUTES OE PROCEEDINGS OE 
suddenly, and tlie conditions are altered, but still there is much 
resemblance; so that we find crushing strength a great desideratum in 
the projectile, and tensile strength equally important in the plate. 
I have mentioned hardness and crushing strength as distinct pro¬ 
perties. They may at first appear to be the same; but while the former 
expresses rigidity in each projectile, the latter refers to rapid connection 
of a mass of particles. Thus glass is harder than iron, and will scratch 
it; but iron has greater crushing strength than glass, and may be made 
to crush it. 
We naturally look for proofs, or at all events indications, of the 
projectiles having exhibited the qualities we ascribe to them in the act 
of performing their work. 
In picking up fragments of Palliser shot after impact against armour, 
two things may be specially observed; one, that the point, however 
much broken, is never flattened, owing to its intense hardness; the 
other, that the fragments are most remarkably cool as compared with 
those of other projectiles, and this seems to prove that its structure has 
been less crushed—for almost all material becomes heated when pressed 
out of shape, or set up. 
There is, however, a disadvantage in having metal in the constrained 
or unnatural condition produced by chilling. I made experiments to 
ascertain the respective densities of shot from the same ladle of metal, 
in chill and in sand, and found the former to be perhaps as much as 
3^ per cent, the denser of the two. Now, the power of molecular forces 
—that is, of the tendencies of particles of any substance to assume any 
condition that circumstances encourage—is gigantic. Thus we know 
shells may be split by water freezing in them, so a Palliser shell may be 
split by filling it with molten iron and allowing it to solidify in the shell. 
Hence it is not very surprising that chilled metal should, under some 
circumstances, assert its right to so far take a more natural form as to 
split or crack the projectile. This frequently occurred with solid shot 
formerly made, and it occurs with shell also. The specimen on the table 
is a shot found cracked so as to be hardly visible until it was split open, 
when the extent of the injury became manifest. Hence it is not sur¬ 
prising that shot and shell should occasionally have broken in the guns— 
the shot, of the two, being perhaps the more likely to wedge in the bore 
and do serious injury. 
For this reason chiefly, it has been found an improvement to chill 
only the head, and form the body of the mould in which the shot is cast 
of sand. This was, I believe, suggested some considerable time ago, 
both by G-eneral Boxer and Mr. Davidson, the manager of the Royal 
Laboratory; and I would especially mention that to Mr. Davidson is 
due in a great measure the actual efficiency of the Palliser projectiles 
as they now exist in the service; and I think I may say that Major 
Palliser is anxious to accord to him the credit of having worked the 
subject out in a way that, perhaps, could hardly have been done by 
anyone else. 
I am not aware of the relative tendencies of white and chilled iron to 
split, but I feel confident that mottled bodies cast in sand are less liable 
to this evil than either* 
