265 
coal, the other materials being the same ; and in the same 
. order each of these fuels contains, each in succession, a greater 
quantity of sulphur and other extraneous ingredients, in 
addition to the carbon. Nevertheless some chemists have 
suggested that iron which has been manufactured with wood 
charcoal, may probably contain potassium, and may owe its 
superiority to this circumstance. Chemists appear, however, 
hitherto to have been puzzled in explaining the phenomena 
of both iron and steel ; for although the best steel is made 
from iron which has been procured from ores containing 
manganese, yet careful and skilful analysis, as far as I 
know, has not been able to discover manganese in steel. 
I may also state what I believe is now no secret, that in the 
processes of improvement by which some English irons have 
been rendered fit for conversion into steel, manganese is a 
principal ingredient. 
The produce of the blast furnace is the cast iron, com- 
monly called pig iron, or pigs. This pig iron is readily 
fusible, and is employed in castings for a vast variety of 
articles, from the bridge over the Thames, to the shirt pin 
and brooch. Its qualities are as various, but concern my 
present purpose only as connected with the qualities of the 
malleable iron made from it. Pig iron, in addition to carbon, 
is supposed to contain oxygen, silicium, and probably many 
other minute and variable alloys. Potash exists in almost 
all our coal measure ironstones. Cyanide of potassium is 
frequently produced in considerable quantities in the blast 
furnace. The most apparent differences in pig iron are 
discovered in its colour; as a general rule, the blackest 
contains most carbon, the grey and mottled less, and the 
white pigs the least. But there are important exceptions. 
Some of the most highly carbonized pig iron is light in 
colour. Its darkness seems to vanish if carbon be present 
in great excess, as in the case of " greasy irons," the 
