411 
Cast SteeL 
But this is precisely the same experiment as that of Mr. 
Mushet’s, related in the preceding paragraph, and M. 
Clouet having entirely overlooked the extrication of gas 
from the metal, has gratuitously attributed the change 
produced to a combination of the iron with a little of the 
glass, without, as appears, taking the trouble to substan- 
tiate his hypothesis by actual analysis. 
Cast iron made with coke instead of charcoal, must 
necessarily contain a variable proportion of sulphur : nor 
is this substance very likely to be entirely dissipated by 
the subsequent refining that the metal goes through ; and 
it appears from a direct experiment by Dr. Beddoes, that 
iron after being puddled and stamped, if treated with mu- 
riatic or sulphuric acid, will give out sulphuretted hydro- 
gen. Bergman has shewn that certain varieties of iron 
contain manganese, and others phosphoric acid. Clouet 
has detected arsenic in some ; and other chemists have 
somewhat obscurely intimated the presence of lead, copper, 
and zinc, which is far from improbable, as several of the 
ores of iron are occasionally mixed with galena, copper 
pyrites and blende. But the effect of these substances in 
small quantity on iron has not yet been ascertained by any 
experiments that can be depended on ; it is therefore ob- 
vious how much remains to be done before we acquire a 
thorough knowledge, even on practical points, of this 
most important of all metals. 
The following, in the present state of our researches on 
this subject, may be laid down as the essential characters 
of the principal forms under which iron exhibits itself. 
Crude cast iron, besides casual impurities contains carbon, 
oxyd of iron, and vitrified earth. The difference between 
white, mottled, grey and black cast iron depends on the 
proportion of carbon, which is smallest in the white and 
greatest in the black. By the process of refining or re- 
smelting, most of the earth and oxyd of iron rises to the 
