Iron, 31 
ilic acid, are usually worked to profit, as in the common 
mountain iron-stone, and the bog- ores. 
The salts of iron (unless the carbonat of iron be so call- 
ed) are never smelted for the purpose of obtaining metal 
Whether an ore be magnetic or not, is no criterion whe- 
ther it be worth working or not. This quality has influ- 
ence only on the quantity of carbonaceous matter necessa- 
ry to metallize the iron. 
As to the quantity of iron contained in an ore. Whe- 
ther it be worth working or no, depends less upon this 
criterion, than upon the circumstances, whether it can be 
easily gotten, and easily and cheaply fixed. The shining 
sulphureous pyrites often contains more than fifty per cent 
of metal, and is not worth working : the poor ore of Staf- 
fordshire, in England, that does not yield more than from 
16 to 20 per cent, is a profitable concern, because it is ea- 
sily reduced to a metalline state, and when so reduced is 
of good quality. 
As to the kinds and proportions of earths with which 
the stone is mixed. Let it be remembered, that, 
The earth that gives the character to common clay, and 
to clay stones is called argillaceous earth. The earth that; 
gives the character to limestone, is called calcareous earth. 
The earth that gives the character, to quartz, flint, whether 
transparent or opaque, to flinty sandstone and stones of 
that hard nature, which scratch glass, and give fire with 
steel, is called siliceous earth. The earth that gives the 
character to soapstone, and stones of that class, that appeal' 
I greasy to tne touch, is called magnesian earth. 
Iron-stones contain the latter in so small proportion for 
the most part, that its effects need not be noticed : but the 
i rest are of great importance to be known ; for whether 
any limestone ought to be added as a flux, or in what pro- 
[ P or ti° n > depends on the kind and quantity of the earthy 
| that envelopes the particles of iron . 
