10 
Iron . 
jnonly a faded blood colour, more or less dark according 
to the quantity of lime present. 
I have repeatedly made use of all the various iron- 
stones, in the state of a fine powder, in order to ascertain 
what was the weight lost by each class in its transition 
from its native hue to the first stage of an assumed colour. 
And I am enabled to state the following as an average of 
the results obtained on this head : Calcareous iron-stones 
give out six parts in one hundred of the raw mineral : 
argillaceous iron-stones, five ; and siliceous iron-stones, 
four and a half. 
If the pulverised iron-stone is thrown into a vessel red 
hot, this loss will be effected in two minutes. The change 
of colour is immediately effected on those parts in contact 
with the heated iron. The whole is brought into contact 
with it ; and when thrown out, the magnet will be found 
to have acquired a perceptible influence over it. When 
the powder is first thrown in, a slight decrepitating noise 
is heard for a few seconds. This operation may also 
serve to shew the presence of sulphur, or of its acid. 
When in the former state it instantly takes fire, and burns > 
with a dark lambent flame. When the acid is present, it 
is easily known by the suffocating fumes disengaged by 
the action of heat. 
The application of heat beyond the first stage of colour, 
causes the iron-stone to pass through a variety of shades. 
These, as in metallic substances, are the effects of the pre- 
sence of air at certain degrees of heat*. As the progres- 
sive dissipation of the volatile mixtures takes effect, the 
colour deepens ; and, according to the nature of the iron- 
* From smooth-surfaced iron-stones and ores, when exposed to 
heat par daily sheltered by charcoal dust from the action of air, II 
have obtained all the shades of colour peculiar to polished iron and 
steel; but with less of the metallic lustre, owing to the surface be- 
ing more porous. 
