Microstructure of Coal from an Industrial Standpoint. 155 
The results are calculated on the dry, ash, and sulphur-free 
-coals ; the volatile matter is the loss on heating to 950° C. in a 
closed crucible surrounded by a larger crucible containing charcoal. 
The calorific value is by bomb determination. 
The use of the microscope is comparative. Typical samples of 
coal which had been proved to be satisfactory, and others which 
were not satisfactory, were taken. Sections were cut in three 
directions and very carefully examined under the microscope. 
Photographs were taken, tinted to correspond to the actual sections, 
and the various coals compared. It was thought reasonable to 
-expect that coals with a similar appearance under the microscope 
would behave similarly in practice. This was borne out in the 
works. It will be seen that it is a matter of experience and 
comparison upon which the method of use depends, and that it is 
not necessary to take into consideration the nature of the consti- 
tuents of the coal for selection purposes, though one does so as a 
matter of interest. It is this comparative treatment which makes 
the method so empirical. Similar work was carried out with other 
classes of coal such as that used for non-recovery producers, steam 
boilers, direct-fired furnaces, coke manufacture, town’s gas manu- 
facture, etc. 
It is quite possible by microscopic examination to pick out 
■coals suitable for these purposes. It is usual to leave the final 
selection until a test has been run under working conditions, and 
in the running of such a practical test it is a great gain to know 
that unsuitable coals have been eliminated. With the ordinary 
methods of examination one can never feel certain, until a large 
scale trial has been run, that the fuel selected is the right one. 
Large scale trials are expensive, and if the coal is not a suitable 
one may have serious results. 
From the study of industrial coal in general use, one is lead to 
the conclusion that it is possible to divide the so-called “ bitu- 
minous ” coals into three main classes. 
One type is composed mainly of wood tissue. I use w T ood here 
in the strict sense, and not as it is generally used to denote timber. 
These are the soft humic coals which swell considerably on heating 
and form a very porous coke. 
The second type has a predominance of spore coats and micro- 
spores. This class of coal is practically non-coking, a property 
which is to be expected when the main bulk of the coal is com- 
posed of spore exines. The “ resinous ” constituent of the humic 
coals which causes them to coke is most probably derived from 
the wood cell contents. This constituent is soluble in pyridine 
and chloroform, but the spore coals yield very little soluble matter 
on treatment with pyridine. 
The third type consists of the hard coals or cannels. These 
are the non-coking long- flame coals, which are dull and compact. 
