22 
Iran. 
ing iron-stones ; some of which will smelt, and give prin- 
ciple to the iron contained in double the weight of the same 
ores that others wilL From this then may be deduced 
another proof, that good and bad iron are terms of compa- 
rative meaning only, confined to situation. Let it be con- 
ceived that a change of fuel opposite in its quality 7 to that 
now mentioned was to take place ; the same quantity of 
ore, which with the good coaks would have afforded metal 
richly carbonated, would now yield its produce in a partial 
degree, and that highly oxygenated— almost unfit for any 
purpose. The consequences here entailed are the same, 
though they may be attributed to different causes; the, 
former as derived from the hostile mixture of the ore, but 
die latter as arising from a deficiency in the quality of the 
coaks. 
Besides these two leading instruments of alteration in 
the smelting process, inherent in and derived from the 
materials, good and bad effects may be produced from an 
unjust proportion and quality of the lime-stone, which is 
added, in order that the proper equilibrium may be resto- 
red, and the iron properly and beneficially revived. 
Taking this then for a general principle, that the crude 
iron contained in all iron-stones is the same, and that it 
can be called into existence as a metal of all the various 
degrees of carbonation, by regulating the proportion of 
fuel, and of the solvent ; I shall proceed to mention those 
mixtures which I have always observed determine the fu- 
ture quality of the crude iron. 
1. Argillaceous iron-stone having fine clay as its chief 
component earth, lime in the next proportion, and both 
these nearly destitute of sand ; which, when properly tor- 
refied, exhibits fibres on its internal surface, of a brown, 
dark brown, or claret colour, running either in streaks or 
radiated, and adhering tenaciously to the tongue, will af- 
ford, with a moderate proportion of coaks and lime-stone. 
