COAL 265 
time apply a lighted taper to the gas, and notice that it 
takes fire and burns as shown at A. The Coal, not having 
access to a sufficient supply of air, when heated does not 
burn, but is resolved into a number of products some of 
which—the gaseous—form the well-known Coal-Gas. It 
is this which burns at the end of the pipe-stem. 
Manufacture of Coal-Gas.—Coal-Gas is prepared by 
what is known as the destructive distillation of Coal. This 
consists in heating the Coal in closed retorts out of contact 
with the air. The retorts, which are made of clay, are 
heated in a furnace, when the Coal is resolved into a variety 
of gaseous, liquid, and solid products which distil over and 
are collected. The volatile products obtained from Coal in 
this manner contain not only the mixture of gases known 
as Coal-Gas, but also a number of substances which must 
be removed before the gas can be used with safety and 
convenience for illuminating purposes. A detailed account 
of the process of manufacture will be found in any text- 
book of Chemistry. 
During the process of manufacture a number of useful 
products are obtained ; amongst these may be mentioned 
Coal-Tar, Ammoniacal Liquor from which most of the 
ammonia of commerce is derived, a number of brilliant dyes, 
and a very sweet substance used in the manufacture of 
certain kinds of confectionery. 
The Gas itself is used chiefly for illuminating and heating 
purposes. 
Lessons on Coal might with advantage lead up to others 
on Coal-mines and Coal-mining. These would be specially 
interesting within reach of Coal-mining areas, where visits 
could be paid to the mines and some of the operations seen 
in progress. It will obviously occur to teachers that it 
would not be a simple matter to arrange for a number of 
children to enter and explore a Coal-mine. Observations 
