207 
Iron, 
remains two intermediate stages of quality to be describ- 
ed : these are, carbonated and carbo-oxygenated iron ; 
that is, No. 2 and 3 of the manufacturers. Carbonated 
iron exhibits, like No. 1, a beautiful appearance in the 
runner and pig. The breakings of the fluid, in general, 
are less fine ; the agitation less delicate ; though the divi- 
sion of the fluid is equal, if not beyond that of the other. 
When the internal ebullition of the metal is greatest, the 
undulating shades are smallest and most numerous : some- 
times they assume the shape of small segments ; some- 
times fibrated groups ; and at other times minute circles, 
of a mellower colour than the ground of the fluid. The 
surface of this metal, exposed to external air, when cool- 
ing is generally slightly convex, and full of punctures ; 
these, in iron of a weak and fusible nature, are commonly 
small in the diameter, and of no great depth. In strong 
metal, the punctures are much wider and deeper. This 
criterion, however, is not infallible, when pig-iron of dif- 
ferent works is taken collectively. At each individual 
work, however, that iron will be strongest whose honey- 
combs are largest and deepest. 
Carbo-oxygenated, or No. 3, pig iron, runs smoothly, 
without any great degree of ebullition or disengagement 
of metallic sparks. The partings upon its surface are long- 
er, and at greater distances from each other than in the 
former varieties; the shape they assume is either eliptical, 
circular, or curved. In cooling, this metal acquires a con- 
siderable portion of oxyd ; the surface is neither marked- 
ly convex nor concave ; the punctures are less, and fre 
quently vanish altogether. Their absence, however, is no 
token of a smooth face succeeding ; in qualities of crude 
iron oxygenated beyond this, I have already mentioned 
that a concave surface is the consequence of the extreme 
absence of carbon ; and that, in proportion as this princb 
