234 
Iron ; 
W edge wood's pyrometer.* Iron, andplatina, are the only 
metals hitherto known that are capable of being welded ;■ 
that is when two pieces of iron are brought to a white heat, 
and placed one upon the other and strongly hammered, 
they become covered with a kind of metallic varnish, and 
may be perfectly united : iron when hot strongly attracts 
the oxygen or pure air of the atmosphere, and puts on a 
blackish blue appearance as in finery cinder,, and smithy 
slack : these scales can be again changed into malleable 
iron by being treated with charcoal, which unites with 
the oxygen and leaves the iron : thin plates of iron may 
also be blued by heat without exposure to air : when ex- 
posed without heat to the air and to moisture, it is chang- 
ed gradually into rust, which is either iron united to oxy- 
gen, or, as I rather believe, to the carbonic acid of the 
atmosphere, which exists in the atmosphere in greater pro- 
portion than is usually suspected. By heating it with 
charcoal, this rust also can be reduced to malleable iron* 
At a full red heat, iron is capable of decomposing water, 
uniting with the oxygen, which forms one component I 
part of water, while hydrogen or inflammable gas which 
forms the other component part, is set free. The iron in 
this process is reduced to the bluish black oxyd of iron 
exactly similar to finery cinder and smithy slack. Mr. 
Watt, of Birmingham, told me some years ago, that iron 
at a white heat, would greedily attract and decompose 
water, if the air in the place were at all moist. These 
are the principal properties of the metal iron when pro-? 
duced by means of the processes I have detailed. 
* The highest point to which I was ever able to raise an air 
furnace with a fuel of coke, was 172° of Wedgewood, at which heat, 
grains of crude platina agglutinated but did not melt ; I have 
them still by me in a lump of about an 1 1-2 oz. weight, T, C, 
