232 
Iron . 
malleability is greatly increased by heat : and by raising 
it to a very high temperature, it becomes exceedingly soft, 
and may be brought so near to absolute contact with ano- 
ther piece similarly heated, that they unite firmly together. 
This process is called welding . Its great affinity for oxy- 
gen, when heated to a welding point, would very soon re- 
duce it to an oxyd, if it were not for the vitreous matter 
fusing upon its surface ; and it may be still more com- 
pletely defended, by dipping it in powdered glass or sand.” 
When pig-iron has undergone either the process of the 
bloomery, puddling, or refinery, to dissipate the foreign 
mixtures which the crude iron contained — to reduce or 
bring to a metalline state, the particles imperfectly metal- 
lized in the furnace— and to burn away the superfluous 
quantity of carbon or charcoal which crude iron always; 
contains in some part or particle of it- — the metal becomes i 
less fusible, and is carried under a tilting hammer, to bed 
beaten while red hot : this process, frequently repeated 
during the period of refining the crude iron into malleable d 
iron, has two principal effects : — -1st. It squeezes out and: 
separates, in the form of slag and scoria, all those particles i 
which have not been perfectly metallized, and which there- 
fore do not unite with the particles that have been perfect- 
ly metallized.— 2d. It gives to the iron a longitudinal 
grain, and very greatly increases its tenacity. When it 
appears to have thus gained the properties of malleable 
iron, it is beaten into bars, and is ready for market as Bar- 
Iron. The loss of weight in this process obviously de- 
pends on the qualities of the pig iron employed. 
In this country, tilt hammers are universally used for 
drawing the iron out of the loops into bars. In England 
they are almost exploded. The work is done by means of 
cast iron rollers : for which purpose (I believe') the fusible 
smooth faced pig iron, No. 1 5 is the best ; though the grey 
cast iron is commonly used. In casting the rollers, the 
