THE ROYAL ARTILLERY INSTITUTION. 
23 
importance of this is obvious, from the fact that it is impossible to 
estimate from the firing point the longitudinal position of the burst, 
which is seen as a cloud in the air.* 
We next come to 
Palliser Projectiles . 
To point out clearly the condition of these projectiles, I must explain 
generally the principles of manufacture, and must apologise for bringing 
together some well-known facts. Iron is hardly to be obtained as pure 
iron—that is, wrought-iron—in the molten condition, but in contact 
with some form of carbon it is readily melted, the carbon so far com¬ 
bining with the iron as to form cast-iron ; the carbon either remains 
combined with the iron, or separates from it more or less in cooling, 
according to its nature. In very white iron it is nearly, if not all, in 
the combined state of some form of carbide of iron; in very grey iron 
it is an intimate mixture of particles of carbon—termed graphite— 
and particles of iron, and intermediate irons range between these 
extremes. Further, it is found that the carbon has a better opportunity 
of separating when the iron is cooled slowly than when quickly cooled ; 
hence, iron which might be mottled if cooled slowly, is obtained as a 
species of white iron when cooled suddenly, or chilled. This, in the 
case of Palliser projectiles, is effected by running it into metal moulds, 
or chills, which, by their great power of conducting heat, carry off that of 
the molten metal so rapidly as to cause it to solidify before the carbon can 
separate from the iron; hence we get the chilled form of white iron. 
I have called it the chilled form of white iron , because it is not 
exactly in the same condition as iron which, from its own tendencies, 
became white, even when cast in sand. If the specimens on the table 
be examined, it will be seen that the chilled specimen is close and more 
silky in its texture than the harsher looking white iron proper; it is 
believed that it exceeds white iron in the degree in which it exhibits 
qualities common no doubt to both, to some extent ; these are— intense 
hardness, great crushing strength , and density . Both chilled and white 
iron are brittle, being deficient in tenacity. 
Examined chemically by Eggertz* test, with nitric acid, the carbon 
would probably be found in much the same condition in both. 
To, bring all these matters to practical results : the crushing strength 
and hardness are found to be exactly what is required to pierce armour- 
plates, with such a form given to the head by Major Palliser as to 
prevent the ill effects of the want of tenacity. 
The action of piercing armour-plates may be compared to the ordinary 
work of punching sheet-iron with a steel punch ; when, if enough force 
is used, something must give way. The punch itself may crush, but the 
crushing or flattening of the sheet-iron is not sufficient to give relief; 
it is necessary that the part in front of the punch should come away 
from the rest, and so let the punch through. Hence the two forces 
opposed to each other are the crushing strength of the punch, and the 
tensile strength of the plate. In piercing armour, the work is done 
* Vide paper by Major-General Gardner, Vol. VI. p. 33. 
