THE KOYAL AETILLEKY INSTITUTION. 
125 
passage of the shot through the plate* and wood backing* any amount of 
motion set up in the particles of the projectile itself is so much force wasted. 
If soft iron shot are fired at iron plates they become intensely heated* while 
the chilled projectile remains cool. If the shot could be picked up imme¬ 
diately after impact* and the amount of heat produced by the effect of the 
blow accurately measured* there would be no difficulty in calculating the 
exact amount of force lost by conversion into heat. The mechanical equiva¬ 
lent of heat is as follows :■—The quantity of heat that would raise lib. of water 
through 1° Pah. is equivalent to 772 foot pounds. Sir W. Armstrong made 
some experiments which probably afford good approximate indications of the 
amount of force expended in heating shot of different degrees of hardness. 
With hard and well-tempered steel shot* the work expended on the projectile 
was about T V h of the total amount of work in the shot on impact. 2. With 
soft steel* about T V hs of work. 3. With soft wrought-iron* about Cast-iron 
eluded observation* as the shot broke up into fragments which could not be 
collected. 
It would therefore be undesirable to sacrifice hardness in order to get a 
more tenacious material. 
Independent of the mode of casting* the manner in which the carbon 
present is associated with the iron depends on the nature of the ore from 
which the iron is smelted. In hard white iron the carbon is chemically 
combined with* and alters the qualities of* the iron; in fact* it is no longer 
iron* but a carbide of iron* not possessing the tenacity of iron* but on the 
other hand gaining the qualities of intense hardness and great strength to 
resist crushing—exactly what is required in the ogival head of a Palliser 
projectile. 
Several causes are known to be favourable to the chemical combination of 
the carbon—such as the presence in the ore of manganese* or sulphur. The 
former action is said to be due to the fact that the carbide of manganese 
resists the high temperature which appears to break up the chemical com¬ 
bination of carbon and iron; the cause of the action of sulphur I have not seen 
stated* but it is known that white iron is produced from ore containing 
pyrites. 
White irons are rather cheaper than the dark varieties* as they are pro¬ 
duced by using less fuel in the blast furnace* for the reason given above* that 
a high temperature breaks up the combination of carbon and iron. 
In the Royal Laboratory* iron of the required degree of hardness is obtained 
by mixing white iron and grey* or by using mottled irons to start with; but 
the former method is the, usual one. Store scrap— i.e., old shell re-melted 
and run into pigs—has also been employed in the proportion of from 20 to 25 
per cent. The smaller shells will bear a larger amount of store scrap than 
the large ones* because the effect of the chill is greater on the smaller body,* 
thus allowing more soft iron to be used. 
A very important part of the manufacture of Palliser projectiles is select¬ 
ing the iron. Nominally* pig-iron is sent in by the manufacturer of a 
certain brand or number; but though this gives a general idea of the character 
of the iron* still there may be a good deal of variation in the degree of hardness. 
* The hole torn through the plate by the front part of the shot is most likely large enough to 
allow for any alteration in form. 
