77 
Iron . 
capable of oxydating their iron— the result would be* 
that the quantity of oxygen combined would be in a rela- 
tive proportion to the fusibility of the mixtures, for a de- 
terminate space of time. The argillaceous iron-stone 
would be found in a given time to have gained least ; the 
calcareous a larger portion ; while the siliceous, contain- 
ing an assemblage of mixture fusible at a degree of heat 
in which the former would remain unchanged, will be 
found to have gained the greatest weight ; but if exposed 
to an high temperature for a sufficient length of time, the 
oxygen absorbed will be in an exact proportion to the iron 
contained in the stone ; only, the siliceous iron-stones ar- 
rive soonest at a high pitch of combination. In the course 
of many experiments I have found the following propor- 
tions to be nearly just, when the quantity of iron contain- 
ed in the respective stones was nearfy analogous. 
Argillaceous iron-stone, which has yielded me 38 per 
cent, in the assay-furnace, first distilled and afterwards 
carefully de~ oxygenated, increased in weight, during an 
exposure to ignited gas for 8 hours in the bottom of a 
deep crucible, 22 per cent. 
Calcareous iron-stone, which afforded a similar quantity 
of metal, and which was subjected to the same train of pre- 
paration, to dispel its volatile mixtures, and unfix its oxy- 
gen, gained in weight nearly 23 per cent. 
Siliceous iron-stones, containing from 36 to 38 parts 
of iron in 100, treated in the same manner, afforded me in- 
stances of an accumulation of weight equal to 24 to 25 
per cent. 
In order more particularly to illustrate the double phe- 
nomenon of iron-stones first losing and then gaining 
weight, I shall insert the treatment of one particular stone 
of each class ; from which a positive judgment may be 
formed of the general operation, and results, peculiar to 
each. 
