126 
MINUTES OF PEOCEEDINGS OF 
This is probably unavoidable, as the iron from a blast-furnace may vary much, 
even though the ore smelted may be the same. All depends on the working 
of the furnace, blast, &c., which is liable to variation. Hence all iron is 
broken up and carefully sorted, the look of the fracture enabling an 
experienced man to tell the hardness of the iron. Store scrap is similarly 
selected after being run into ingots. 
Different mixtures of Bidsdale and Cwmbran irons (either white or high 
numbers of pigs) have been used in combination with about 20 per cent, of 
store scrap. 
It has become very desirable lately, on the score of economy, to use up the 
large existing store of S.B. guns and projectiles. The price of the iron 
has by this means been reduced to about half, while a recent trial at Shoe- 
buryness against armour plates shows that the projectiles compare favourably 
with those made up with the more expensive mixture. 
Many experiments were carried out in the Boyal Laboratory, and con¬ 
siderable difficulties were experienced, as it was found difficult to get a 
mixture containing much old gun and shell iron to chill properly. 
The addition of ilmenite*—an ore of iron in combination with titanic acid— 
was found to bring the mixture of iron to a state favourable for the process 
of chilling, and since October, 1874, shells have been cast of iron consisting 
chiefly of old gun and shell iron;t something under 10 per cent, of Bidsdale 
white iron, and about 5 per cent, of ilmenite are added. 
The process of chill casting has been well known for a long time, but to 
Major Palliser is due the credit of the application of this method to projec¬ 
tiles, thereby effecting a very large saving by substituting Palliser projectiles 
for steel—which are very costly, and unless great care was taken in the 
manufacture, apt to be uncertain. 
The process consists in casting the metal in iron moulds, the whole process 
turning on the conducting power of the metal, which causes the casting to 
cool rapidly, and thus favours the carbon remaining in chemical combination 
with the iron. Bapid cooling is always unfavourable to the formation of 
large crystals, and there seems to be something analagous in its not allowing 
the carbon to crystallise out into the graphitic form which it assumes when 
the metal is slowly cooled. The result on the metal is to make it intensely 
hard, dense, and brittle, of great strength to resist crushing, and showing a 
brilliant white fracture. Two points are necessary to attend to—to heat 
the chill before beginning to cast, and not to pour in the metal too hot. The 
first prevents the metal being defective where it comes in contact with the chill. 
If it is quite cold there are apt to be flaws, &c.—in fact, the suddenly cooled 
iron will form “ shots ; 33 also, the chilling is found not to penetrate so deep. 
If the second precaution is not taken, the hot metal injures the chill, and as 
* Ilmenite lias been analysed by the Chemist, Wav Office, with the following result:— 
Iron oxide, equivalent to 45'3 metallic iron . 61*4 
Titanic acid . 33’2 
Silica. 4-2 
Tin oxide ....... 1*2 
Manganese . Trace. 
-j- The guns are nearly cut through in a lathe to convenient lengths, and then broken up under a 
steam hammer. 
