76 
Iron , 
weight in the latter was entirely owing to it abstracting 
the metal from the former. Widely different indeed 
would be the conclusion. He now would have learned 
that metals are combustible bodies ; that under certain 
circumstances iron is one of the most inflammable in the 
group ; that, during its combustion, it decomposes the 
air that maintains the combustion, and fixes one of its ele- 
ments in spite of the powerful affinity exerted upon it by 
the caloric ; and that by this process alone it increases its 
volume and weight. The porous mass of iron-stone 
would now be described as having had its iron complete- 
ly saturated with oxygen at a very high temperature ; 
that an imperfect state of fusion had been the consequence ; 
and that a combination of these circumstances, acting for 
p considerable length of time, had volatilised and carried 
off a very considerable portion of the metaL 
On the same principle would be explained the increase 
of weight in the more ponderous piece ; it would then 
readily be conceived, that the same association of circum- 
stances had not been present ; but that the iron had gain- 
ed in weight by the addition of oxygen at a temperature 
short of fusing and volatilising the oxyd. 
Having in the former part of this paper stated the ave- 
rage loss which the various natures of iron-stones sus- 
tain when exposed to torrefaction in external air, I shall 
now simply state the quantity of oxygen which the various 
classes are apt to imbibe when exposed to a high tempe- 
rature, after those volatile mixtures capable of assuming 
the gaseous state by the combination of caloric have been 
expelled. 
The facility with which iron-stones become oxydated 
is entirely dependent upon the nature of the mixture con- 
stituting fusibility or otherwise : so that were argillaceous, 
calcareous, and siliceous iron-stones, previously de- oxy- 
genated, exposed to the same degree of heat— a degree' 
