METALS 281 
out—Iron is ductile. Show pieces of Lead, Copper, Iron 
wire—also thin sheets of these metals, and lead pupils to 
recognise the same properties in each. Metals are mal- 
leable and ductile. Refer to some well-known minerals 
—Coal, Salt, Sulphur. Are these malleable and ductile ? 
What then is the great distinction between a mineral and 
a metal? Kduce from softening caused by moderate heat 
of gas flame or fire, that at greater heat they melt—Iron 
is fusible. 
Wrought Iron is extremely tough and strong and is used 
in cases where these properties are essential. All kinds of 
farm tools—ploughs, harrows, etc.—are chiefly made of it ; 
all kinds of smith-work are composed of it, as well as nails, 
screws, etc. 
Cast Iron. Compare the hardness of Wrought. and Cast 
Iron. Notice that the file readily bites into the former, 
but barely scratches the latter. Cast Iron is harder than 
Wrought Iron. 
Take a piece of old saucepan and strike it sharply with a 
hammer ; observe that it breaks into pieces with a rough 
uneven fracture. Test a piece of Wrought Iron in the 
same way. Notice that it does not break—Cast Iron is 
brittle. 
Try to bend one of the larger fragments of the broken 
saucepan and ascertain that it remains rigid. Apply the 
same test to a piece of iron hooping or iron wire. Observe 
that it can be bent without breaking. Co..tinue to bend it 
backwards and forwards until it breaks and notice that 
whereas the fragment of cast iron snapped clean through, 
the wire or hoop-iron leaves fibrous ends, shewing a kind 
of stringy composition. Cast Iron is not flexible. 
“duce the uses of Cast Iron, which is much cheaper than 
Wrought Iron, It is used where rigidity is required and 
where toughness is not essential, e.g., for making grates, 
