Mr Mushct on the Dcox'idaVwn of Iron-Ores^ ^c. 231 
was a mixture of the oxide of iron A^ith. various earths, chieiiy 
clay, lime, and silex. 
Some time since there appeared in Dr Thomson’s Annals of 
Philosophy, the analysis of an ironstone, wherein it was stated, 
that the iron did not exist in the state of an oxide, but in that 
of either a carbonate or a hydrate. As I Avrite from recollec- 
tion, and cannot refer to the work, I am uncertain Avhich, nor 
is it at all material, as the facts I wish to investigate arc these, 
first. Whether the iron contained in the ironstone so universally 
diffused over this country, does or does not exist in the state of 
an oxide? and, subsequently, if it do so, to establish the extent 
of the oxidizement. 
I think Dr Thomson and most others avIio have examined 
the deep red-coloured ores of Cumberland and Lancashire, 
have agreed that these are oxides of iron, and, as far as my 
own experiments go, there can be no doubt on the subject. If 
these ores are compared with the common ironstone before 
burning, no two substances of the same class can appear more 
dissimilar, and after making a considerable allowance for the 
Avidely different proportions of iron in each, the examiner feels 
inclined to assign to it a very different state of existence. This 
striking contrast, however, is materially lessened Avlien the iron- 
stone has been exposed to the fire ; it then passes from a greyish 
or blackish-blue, (its native colour,) and assumes various shades 
of brown, red or purple, the intensity of which depends on the 
quantity of iron present, the administration of the dose of heat, 
and the length of the exposure. 
The art of roasting ironstone (technically called its Calcina- 
tion,) has by some been considered ^s an operation in Avhich, 
for the first time, the ironstone unites Avith a portion of oxygen, 
and in so far as this requires to be again removed in the smelt- 
ing furnace, previous to separation, it has been deprecated or 
thought unnecessary. Practice, however, has more clearly in 
this, than in any other metallurgical operation, determined the 
utility and necessity of roasting the ores, previous to their being 
smelted. 
After considering the subject again, and referring to many 
other experiments, I remain still of ray former opinion, that 
the common ironstone of this country has united Avitli its iron 
