52 ADVANTAGES OF GAS. 



ADVANTAGES OF GAS. 



ALL substances, whether animal, vegetable, or mineral, consisting of carbon, 

 hydrogen and oxygen, when exposed to a red heat, as we have already seen, 

 produce various inflammable elastic fluids, capable of furnishing artificial 

 light. We perceive the evolution of this elastic fluid during the combustion 

 of coal in a common fire. The coal, when heated to a certain degree, swells 

 and kindles, and frequently emits remarkably bright streams of flame, and 

 after a certain period these appearances cease, and the coal glows with a red 

 light. 



The flame produced from coal, oil, wax, tallow, or other bodies which are 

 composed of carbon and hydrogen, proceeds from the production of carbu- 

 retted hydrogen gas, evolved from the combustible body when in an ignited 

 state. 



If coal, instead of being burnt in the way now stated, is submitted to a 

 temperature of ignition in close vessels, all its immediate constituent parts 

 may be collected. The bituminous part is distilled over, in the form of coal- 

 tar, etc., and a large quantity of an aqueous fluid is disengaged at the same 

 time, mixed with a portion of essential oil and various ammoniacal salts. 

 A large quantity of carburetted hydrogen, carbonic oxide, carbonic acid, and 

 sulphuretted hydrogen, also make their appearance, together with small quan- 

 tities of cyanogen, nitrogen, and free hydrogen, and the fixed base of the coal 

 alone remains behind in the distillatory apparatus, in the form of a carbona- 

 ceous substance called coke. An analysis of the coal is thus effected by the 

 process of destructive distillation : the products which the coal furnishes may 

 be separately collected in different vessels. 



The carburetted hydrogen, or coal-gas, when freed from the obnoxious 

 foreign gases, may be propelled in streams out of small apertures, which, 

 when lighted, form jets of flame, which are called gaslights. 



In order to apply this mode of procuring light on a large scale, as now 



