343 
of the magnetical Pyrites, &c. 
carburet of iron called steel, to the above sulphuret and phosphuret, 
a very remarkable analogy is established between the effects pro- 
duced on iron, by carbon, sulphur, and phosphorus. 
Carbon, when combined in a very large proportion with iron, 
forms the carburet of that metaf, called plumbago; a brittle 
substance, insoluble in muriatic acid, and destitute of magne- 
tical properties. But, smaller proportions of carbon, with the 
same metal, constitute the various carburets included between 
black cast iron and soft cast steel ;* bodies which are more or 
less brittle, soluble in muriatic acid, and more or less susceptible 
of magnetical impregnation; some of them form the most 
powerful magnets hitherto discovered. 
Sulphur, in like manner, combines with iron in a large pro- 
portion, forming the common pyrites, which are brittle, almost 
or quite insoluble in muriatic acid, and devoid of magnetical 
properties. Sulphur in smaller proportions, forms sulphurets 
# “ When the carbon exceeds, the compound is carburet of iron or plumbago : when 
“ the iron exceeds, the compound is steel, or cast iron, in various states, according to 
* c the proportion. All these compounds may be considered as subcarburets of iron.” 
Thomson’s System of Chemistry, Vol. I. p. 165. 
Mr Mush et, in the following Table, exhibits the proportion of charcoal which 
disappeared, during the conversion of iron to the different varieties of subcarburet 
known in commerce. 
Result. 
Soft cast steel. 
Common cast steel. 
The same, but harder. 
The same, too hard for drawing. 
White cast iron. 
Mottled cast iron. 
Black cast iron. 
<e When the carbon amounts to about 5 * 5 of the whole mass, the hardness is at the maxi- 
“mum.” Thomson, Vol. I. p. 166; and Phil. Magazine, Vol. XIII. pp. 142 and 148. 
mdccciv. Y y 
‘Charcoal absorbed. 
i4o 
T§3 
So 
a? 
10 
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