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A mixture of iron pyrites (sulphuret of iron Fe S) is fre- 
quently found in coal, and is very objectionable, from the 
action of its sulphur on the iron bars of furnaces, &c. 
Coal yields from 1 to 30 per cent, of ashes, but usually 
less than that obtained from peat or brown coal. Its specific 
gravity is about 1.3 on the average. Anthracite, a common 
formation in the older series in Wales, is eminently homo- 
geneous, and without impressions of plants, and consists 
almost entirely of carbon; the amount of its ash varies 
from 1 to 6 per cent. 
Time will not admit of my describing now the varieties 
of fuel resulting from subsequent artificial preparation of 
these natural fuels, as coke, charcoal, &c. I cannot, how- 
ever, pass over the subject of patent fuels. The brittle 
nature of our coal deposits, and the difficulty of combustion 
attending coal so mechanically divided as to exclude the 
free circulation of air, has caused the accumulation of vast 
heaps of small coal at the mouths of our coal pits. Several 
patents have recently been taken out proposing to convert 
this, by various processes, into a useful and economical fuel. 
The most extensively employed of these patent fuels is that 
of Mr. Wylam. A brief sketch of this fuel, with the results 
of experiments on its composition, will suffice to give a 
general idea of the whole. 
He first distils coal tar, in a large iron retort, furnished 
with suitable condensers, into naphtha, dead oil, and pitch. 
The naphtha being the most volatile, passes over first, and 
is re-distilled at a temperature of 212° by steam, and after 
admixture with chloride of calcium (Ca CI) or quick lime 
(Ca O), and a third distillation, becomes perfectly colourless 
and fit for sale. The dead oil obtained as the second pro- 
duct of distillation, is used extensively for the purpose of 
illuminating manufactories and other large works; as a 
solvent for pitch, thus forming a valuable varnish ; and 
