THE EOYAL AETILLEEY INSTITUTION. 
233 
as much as possible into a uniformly increasing pressure, the brittle nature 
of the material would not be of much consequence/'’* 
As regards the distinctive features of the two projectiles, we know from 
extensive experience with shot cast in chill, and returned from out stations 
and abroad to be broken up, that in the majority of cases the chilled effect 
was sensible only to a very small and uncertain depth; that, in fact, the shot 
were generally only more or less surface, or case-hardened. Major Palliser's 
chilled shot, on the other hand, have a uniform and characteristic struc¬ 
ture. A section of one of these shot exhibits chilling effects through and 
through, in some cases the actual centre of the shot being allowed to shade 
off into grey iron.f A perfectly definite result is thus always aimed at, and 
can, with little difficulty be obtained, and herein, as will presently appear, lies 
one of the advantages of chilled projectiles. 
Here, then, we have an important and characteristic distinction between 
shot cast in chill and chilled shot. The former have an uncertain fracture, 
in which grey iron more or less predominates, in which, indeed, in some 
cases, white iron is scarcely discoverable; the latter have a fracture of almost 
unvarying uniformity—a fracture in which grey iron is scarcely perceptible, 
and from which, in recent castings, it has been altogether eliminated. The 
one, in fact, was a mass of iron which from an accident, as we may express 
it, in manufacture had become externally hardened to a greater or less 
extent; the other is a mass of iron designedly made for a particular purpose, 
of a definite and carefully determined hardness and structure throughout. 
We have next to examine the causes of this remarkable difference in projec¬ 
tiles, the processes of manufacture of which so closely resembled one another; 
and we here touch still more nearly Major Palliser's claims to originality. 
When shot were cast in chill for the convenience or benefit solely of the 
manufacturer, the character of the iron employed was little studied; but in 
the Palliser projectiles, where not the manufacturers but the artilleryman's 
interests are studied, this is a point of foremost importance. Extensive 
experiments have clearly established not only that certain irons will scarcely 
chill at all,J but have pointed out exactly what those irons are, and have 
supplied perfectly definite and reasonable results respecting the fractures and 
characteristics of a variety of irons and mixtures of irons treated by the 
chilling process. By the light of these experiments we now know almost to 
the fraction of an inch the depth to which the various brands of grey iron may 
be chilled; while we have discovered, on the other hand, that it is possible to 
use too hard an iron—an iron so hard that it will be liable to “over chill," and 
crack in cooling. It is between the extremes indicated by these data that if we 
would produce a serviceable chilled shot, the mean must be struck; and this 
* Letter to Mechanics’ Magazine, July 21st, 1864. 
f The only object of making the shot slightly grey in the centre is as a check, to prevent the 
manufacturer erring on the side of excessive hardness. For a long time this check was always 
employed, but recent experiments have seemed to indicate the desirability of chilling right through. 
X Indeed, it is stated on good authority, that some grey irons will not chill at all: “Not all grey 
iron can be converted into white by this means.”—Percy’s Metallurgy , p. 117. See Ibid, for 
experiment establishing this fact. 
