A PIECE OF COAL. JQJ 
they escape again give back the sunbeams in a bright 
flame. The hard stone coal, such as anthracite, on the 
contrary, has lost a great part of these oils, and only 
carbon remains, which seizes hold of the oxygen of the 
air and burns without flame. Coke is pure carbon, 
which we make artificially by driving out the oils and 
gases from coal, and the gas we burn is part of what 
is driven out. 
We can easily make coal-gas here in this room. I 
have brought a tobacco-pipe, the bowl of which is 
filled with a little powdered coal, and the broad end 
cemented up with Stourbridge clay. When we place 
this bowl over a spirit-lamp and make it very hot, the 
gas is driven out at the narrow end of the pipe and 
lights easily (see Fig. 55). This is the way all our gas 
FIG. 55. 
is made, only that furnaces are used to bake the coal 
in, and the gas is passed into large reservoirs till it is 
wanted for use. 
You will find it difficult at first to understand how 
coal can be so full of oil and tar and gases, until you 
have tried to think over how much of all these there is 
