converting cast into malleable Iron. 265 
very considerable obstacle to the change of charcoal into air ; 
and as I have already observed, the iron probably holds the 
charcoal more strongly as its quantity diminishes. In this 
state of things a small additional impediment will prevent the 
heat from throwing the charcoal into the state of air ; and 
some degree of pressure must be adequate to this effect : and 
why may not this point, from which as you recede on op- 
posite sides, the attraction of the particles of charcoal for one 
another, or for iron, either shall or shall not be overcome by 
heat, have been found in these experiments ? The next consi- 
deration will both illustrate and confirm these ideas. 
3. A chymist, whose notions of iron are derived principally 
from books, and from the phenomena which are presented 
by processes not having metallurgy for their immediate ob- 
ject, will be apt to consider some things related above as in- 
consistent : the violence of the heat, for instance, and the 
smallness of its effects ; since even cast iron was not fused in 
all the experiments. The fact is, when cast iron exposes a 
large surface, and heat is gradually applied, it proves almost as 
infusible as malleable iron : indeed, by the gradual action of 
heat it is converted, superficially at least, into malleable iron, 
or approximates towards it : and considering only iron and 
charcoal, I believe, the fusibility of iron will be directly as the 
quantity of charcoal it contains. Now in the experiments I have 
described, pieces of one, two, and three drachms, and sometimes 
less, were used, for larger could not be inserted into the neck 
of the retort. And, in order to avoid this inconvenience in 
future, I would recommend cylinders to be cast, of a diameter 
suited to the mouths of the vessels. This infusible coat would 
be an impediment to the conversion of the parts below, by 
