130 
MINUTES OF PROCEEDINGS OF 
COMMON SHELL. 
Iron used for Shells. 
The quality of the iron mainly depends on the quantity and condition of 
the carbon associated with it. The various impurities—such as sulphur, 
silicon, phosphorus, &c.—which are generally found in pig-iron, are more or 
less injurious. Sulphur is thought to diminish its strength, but is sure to 
be present, as the fuel—coke—is not free from it; phosphorus may not be 
so injurious, and is said to increase its hardness and fusibility; while silicon 
is said to diminish its strength. The three classes of iron—cast-iron, wrought- 
iron, and steel—run into one another so that it is hardly possible to lay 
down a fixed line. 
Cast-iron contains generally from about 5 to 2 per cent, of carbon. 
(“Spiegle eisen” contains as much as 4 per cent, chemically combined carbon.) 
It would seldom be found to have over 3'7 per cent. Steel would contain 
from about 1*4 to *25 per cent., and wrought-iron from *25 to a trace. 
Tensile strength per square inch :—Cast-iron, from 5 tons to 14 tons; 
wrought-iron, along the fibre, 22 tons; steel, cast, 40 tons; Bessemer steel, 
from 40 to 64 tons. 
Crushing strength:—Cast-iron, from 22 tons to 58 tons. 
All the above figures must be taken only as approximations. 
Pig-iron is used in the manufacture of shells. It is sometimes classed by 
numbers from 1 to 8, 1 being the softest. - * (The price of No. 1 is rather 
higher than the others.) The same ore will produce different varieties of pig, 
according to the working of the furnace. The white is produced by diminishing 
the proportion of fuel employed in smelting the ore. (It is said that the 
high temperature causes the chemically combined carbon to separate from 
the iron, and on cooling it assumes the form of graphite.) The nature of 
the ore has also some influence on the condition! of the carbon. Thus, if 
manganese is present, white iron is more likely to be formed ;J as the carbide 
of manganese resists the action of the high temperature, and when dissolved 
in the iron probably produces the same effects as the carbide of iron. The 
quality of the iron does not simply depend on the amount of carbon present, 
but on the manner in which it is combined. Thus, if it exists in the form 
of graphite, the iron will be grey in appearance, and will have more of the 
qualities of pure iron— i.e. } would be soft and tenacious—while, if the carbon 
is chemically combined, the iron becomes very white, hard, and brittle; 
it is also more dense. Lying between these extremes is mottled iron; so 
& “ Construction of Artillery,” Mallet, p. 231. No. 1 pig, soft, very dark grey in colour, very fusible, 
containing a very large portion of uncombined carbon in the shape of graphite, diffused in scaly or 
micaceous crystals through the mass, upon which it confers its peculiar form of large, pretty uniform, 
but irregular and ill-developed crystallisation, with its dark grey metallic lustre relieved here and 
there by light reflected from the flat faces of spangle-like crystals, some of which can often be 
separated and thrown away from the surface. This pig is the most fusible and liquid when melted, 
the least rigid and tenacious, and the softest when cold. 
•j* Sulphur is said to favour the production of white iron. 
j Pyrites in blast-furnace has long been known to produce white iron. Mallet’s “ Construction of 
Artillery,” p. 226. 
