145 
determination of the quantity of hydrogen and carbon, which 
are the combustible constituents of coal, has really very little 
to do with forming an estimate of their value, except in cases 
where the difierences are very wide. The great use of 
chemistry, is in determining the quantity of sulphur and phos- 
phorus, contained in the coals intended to be used for the 
manufacture of iron, with a view to rejecting all coals con- 
taining a large quantity of those substances. The uses to 
which coal should be put, with furnaces as at present con- 
structed, depends in a great measure, on the rapidity with which 
it is intended to consume it — that is, the greater or less 
intensity of the fire, and whether it will coke or not, and if it 
will, upon the kind of coke the coal will produce ; upon the 
ash, and the temperature at which it melts ; upon the sulphur 
and phosphorus it may contain ; and on the physical con- 
dition of the coal as to hardness, manner of cleavage, &c. 
According to Dr. Percy,* analysis cannot show whether a 
coal will coke or not ; and my own opinion is, that this pro- 
perty, while of course it depends partially on the chemical 
constitution of the coal, depends also, in a great measure, 
upon its structure, modified by geological changes and dis- 
turbances. It appears probable, that if a good, clean coal 
does not coke, the whole of the coals above and below it in 
that locality, will be similarly influenced, other conditions 
being the same. I know a locality in the neighbourhood of 
Leeds, where the coals are considered as non-coldng, and yet 
the same seam of coals will make good coke about three miles 
distant to the north-west. Coals have not only the planes of 
bedding, which are often somewhat irregular, but they have 
a vertical plane of cleavage, which is, speaking general!}', in 
this district about north-east and south-west, but it is very 
variable. I think it possible, that this cleavage plane has 
been produced by the lateral pressure which caused the ele- 
* Dr. Percy's Metallurgy, Article — Fuel, p. 308. 
