COAL 957 
a 
Note.—Most of the carbonates are acted on very 
slowly unless the acid be heated. 
Notrt.—This brief account of the properties which are to be 
looked for in minerals is intended as an indication of the way in 
which the examination of a mineral may he set about. It would 
be unwise in each investigation to apply all the tests suggested. 
With a little practice the properties likely to be found in the 
specimen under review will suggest themselves, and these, as well 
as others of which the investigator is doubtful, can be tested. It 
is not necessary, moreover, to test for the properties in the order 
given, so long as the properties themselves are discovered, it does 
not much matter in what order the discoveries are made. It will 
be found convenient to take certain groups of tests together—for 
instance, brittleness, hardness, cleavage will obviously form one 
group. 
IJ.—COAL. 
INTRODUCTION.—The word Coal is a popular, rather than a 
scientific, term, and is applied to a number of different substances 
which agree in being more or less pure varieties of uncrystallised 
Carbon, and which have been formed by the compression of old land 
vegetation into the material which is now used as fuel. Coal is 
not a mineral substance in the same sense as Slate or Marble, as it 
is of vegetable origin ; still its mode of occurrence and general 
properties cause it by common usage to be regarded as a mineral. 
A little thought will convince anyone that it is more convenient 
to include it amongst the minerals than amongst the plants. 
Physical Properties.—Show a piece of common Coal, 
and let the pupils discover for themselves its physical and 
chemical properties. 
They will begin by describing in general terms the shape 
of the specimen, ¢.g. its size, irregular surface, angular pro- 
jections, etc., ete. This is a most necessary preliminary in 
all examinations of minerals, and should on no account be 
omitted. They will then note whether or not it can be 
handled without soiling the fingers. Some kinds of Coal 
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