ARMOURED DEFENCES* 
333 
Armour plate iron is not made for very high tensile strength, hut it 
is essential that it should draw out well, and reduce in cross section 
some 20 or 30 per cent, before breaking. 
It has been our practice to prove a very large proportion of the 
plates made for iron fortifications by shot capable of nearly perforating 
them. Pieces of those which could not be thus proved have been 
broken under hydraulic presses, and otherwise treated. 
Armour bolt-iron is similar to armour plate-iron, but we require a 
reduction of area of fracture of at least 40 per cent, when broken by a 
falling weight test, and we generally get a larger reduction than this. 
As forged (hammered) iron-armour plates are obsolete, I need not 
describe their manufacture. 
As regards chilled cast-iron there is not much to be said, further Manufac- 
than that Herr Grriison, the principal manufacturer of it, runs his blocks, cSmed cast- 
for fortifications, direct from cupolas into sand moulds, chilling the iron armour * 
faces which are to form the fronts of the blocks against masses of cast- 
iron. Some of the chills are twice the weight of the casting itself; the 
chill generally extends two or three inches into the metal. Single 
blocks have been used as heavy as 50 tons. The cost of these blocks 
may be taken as rather more than half the cost of wrought-iron armour 
plates per ton, but then the cast-iron has to be used in masses more 
than twice the thickness of the wrought-iron which would give the 
same protection. 
With regard to compound plates there is more to be said, but I Manufac- 
must condense it into a few words. compound 
All the most successful compound plates have been made of ordinary P lates - 
armour plate iron faced with Bessemer steel. Of course an equally, or 
even better, face might be given by using crucible steel, but the cost 
and difficulty attending the use of this kind of steel would be enor¬ 
mous. In fact, I think it may be said that but for the Bessemer and 
Martin- SiemeAs processes, it would have been practically out of the 
question to make compound plates at all. 
The most simple and effective process of manufacture of these plates 
is as follows :— 
First, a rolled iron armour-plate of the usual quality is made, and on 
it is laid round its edges a wrought-iron frame, the thickness of the 
armour-plate and the depth of the frame depending upon the thickness 
required in the finished plate. 
The plate and frame are then placed in an ordinary plate-heating 
furnace, and when at a welding heat they are brought out, and molten 
steel made by the Bessemer process is poured out of large ladles on to 
the surface of the plate up to the brim of the frame. The mass is then 
allowed to cool, and is afterwards re-heated and rolled down into an 
armour plate of the desired thickness. The edge of wrought-iron is 
afterwards planed off. Instead of having a simple frame round the 
edges of the plate it has been proposed to subdivide the surface into 
squares, as those of a chess board, in order that, by breaking the 
continuity of the steel, the cracks caused by shot blows may be stopped 
short, and with the same object an officer of R.A. has proposed to 
subdivide the steel by fine cuts across its face ; but we have not yet seen 
the effect of these expedients in actual trial. 41 
