Iron , 
231 
views, we shall unquestionably find that it will be much* 
more economically accomplished* 
When iron has been completely freed from carbon, and 
has acquired its highest degree of malleability by repeat- 
ed hammerings, it is by far the most tenacious of all the 
metals, and is capable of being drawn into the finest wire. 
The tenacity of iron, as well as of all the rest of the 
malleable metals, varies considerably according to its soft- 
ness* After iron has been kept in a red heat for some 
j time, and suffered gradually to cool, it becomes remark- 
ably changed in point of softness* By being hammered, 
drawn into wire, or rolled, it increases in hardness to a 
j certain extent ; but, at the same time partly loses its mal- 
! leability « By this mechanical treatment, when cold its 
1 strength or tenacity increases ; and it may be taken at 
one point, when it will require a far greater weight to 
break it, than if it were hammered either more or less* 
All the experiments yet published relative to the tena- 
city of iron, and the other metals, are on this account very 
defective* The writer of this article has seen an iron 
wire, when newly annealed, break with a weight of 50 
pounds ; but, after being drawn through two holes of a 
! wire plate, bear above twice that weight, without sustain- 
I ing injury. Iron, when properly annealed, will bear more 
bending backwards and forwards before it breaks, than in 
j any other state : but the strength, or that power which 
!; resists a weight, exerted longitudinally to break it, is joint- 
ly as the last property and its hardness* Hence the reason 
why its strength is increased with a certain degree of ham- 
mering. The specific gravity of malleable iron, accord- 
ing to Brisson, is 7,788 ; that of pig-iron being 7,207. 
Iron, in a state of purity, requires so great a heat for its 
fusion, that the best crucibles are nearly ready to melt 
with it. It has however, been fused, and cast into an in- 
got. It is said to liquify at 158° of Wedgewood. Its 
