Iron . 
57 
obtained with a superior mixture of clay, in all its stages 
of quality, possesses a greater degree of strength than iron 
from calcareous iron-stones. Iron from argillaceous iron- 
stone is reckoned strongest when carbo- oxygenated ; that 
extracted from calcareous iron-stone is reckoned to pos* 
sess most strength when oxygenated, mottled/*” I would 
far exceed the limits of the present communication, were 
I to enter fully into this curious subject, and particularise 
the different results obtained by the fusion of ores with dif- 
ferent earths in various proportions : all my experiments 
have fully proved to me, that originally the quality of the 
iron, simply considered, was the same ; that, as it under- 
went change by decomposition and new combination, it 
became united to foreign substances, possessing widely 
different properties ; and which mixture, by a general fu- 
sion, imparts to the metal various properties, seldom ho- 
mogeneous, but frequently otherwise : in short, that the 
numberless mixtures with which it is combined are not 
neutral in fusion, but convey an alteration to the quality of 
the reduced iron* I hope to resume this subject when 
my experiments will be more extended by the examina- 
tion of a vast variety of iron-stones, and shall then point 
out the consequent effects of their application to the ma- 
nufacture of cast and malleable iron. 
The assaying of primary oresf comes next under consi- 
deration* These, I have already said, possess a much 
greater diversity of external character, as well as internal 
variety, than those of iron-stone. When assayed with a 
vitreous flux, either of salts, alkalies, or silex, the results 
are rendered very uncertain and erroneous : when pot-ash, 
tartar, See* are used, the crucible is often destroyed, and 
the compound entirely lost : when bottle glass and a mix- 
ture of these are used, the scoria formed is so very black 
* I cannot comprehend this. T. C. 
t Ores found in primitive formations, T. €- 
H 
