COAL-GAS. 



375 



in lime kilns, and is a very deadly one. We must now pass rapidly through 

 the compounds of carbon with hydrogen, merely referring to coal for a 

 moment as we go on. 



Coal, of which we shall learn more in Mineralogy and Geology, is a com- 

 bination, mechanical or otherwise, and is the result of the decomposition of 

 vegetable matter in remote ages, the so-called " forests," which were more 

 like the jungles than the woods of the present day. Moss and fern played 

 prominent parts in this great transformation, as we can see in the Irish peat- 

 bogs, where the first steps to the coal measures are taken. 



The compounds of carbon with hydrogen are important. There is the 

 " light " carburetted hydrogen (CH 4 ), which is usually known as fire-damp 

 in coal mines. It .is highly inflammable and dangerous. The safety-lamp 



ijJ- 374-~ Experiment showing that carbonic acid contains oxygen and carbon. 



invented by Davy is a great protection against it, for as the gas enters it is 

 cooled by the wire, and burns within harmlessly. The explosion warns the 

 miner. " Heavy " carburetted hy- 

 drogen possesses double the quantity 

 of carbon (C 2 H 4 ). It is also explo- 

 sive when mixed with oxygen. 



The most useful compound is 

 coal-gas, and though its principal 

 function appears to be in some 

 manner superseded by electricity, 

 " gas " is still too important to be 

 put aside. It can easily be obtained by putting small fragments of coal 

 in the bowl of a tobacco-pipe, closing the bowl with clay, and putting it in 



Fig. 375. Temperature reduced by contact with wire. 



