ADVANTAGES OF GAS. 53 



practised with such brilliant success in this country, as well as in many parts 

 of America and continental Europe, the coal is put into vessels called retorts, 

 and furnished with pipes connected with reservoirs, to receive the distillatory 

 products. The retorts are fixed into a furnace, and heated to redness : the 

 heat developes the gaseous and liquid products of the coal : the latter are de- 

 posited in receivers or tanks, and the former conducted through lime-water, 

 or thin strata of the hydrate of lime, and purified. The sulphuretted hydrogen 

 and carbonic acid, which are mixed with these, become absorbed by the lime 

 and moisture, and the pure carburetted hydrogen is stored up in a vessel called 

 a gasometer, and is then ready for use. From the reservoir in which the gas 

 has been collected proceed pipes, which branch out into small ramifications, 

 until they terminate at the place where the lights are wanted ; and the ex- 

 tremities of the branch pipes are furnished with stop-cocks, to regulate the 

 flow of the gas into the burners or lamps. 



The production of gas-lights is therefore analogous to that of flame pro- 

 duced from tallow, wax, or oil. All these substances possess, in common 

 with coal, the elements of certain peculiar matters, which are capable of being 

 converted into inflammable elastic fluids by the application of heat. 



The capillary tubes, formed by the wick of a candle or lamp, serve the office 

 of the retorts, placed in the heated furnace in the gas-light process, and in 

 which the inflammable gaseous fluid is developed. The wax, tallow, or oil, 

 is drawn up into these ignited tubes, and is decomposed into carburetted hy- 

 drogen gas, and from the combustion of this substance the illumination pro- 

 ceeds. In the lamp, as well as in the candle, the oil or tallow must therefore 

 be decomposed before they can produce a light ; but for this purpose the de- 

 composition of a minute quantity of the materials successively is sufficient to 

 give a good light : thus originates the flame of a candle or lamp. 



Nothing more therefore is required in the gas-light process which coal 

 affords, when submitted to a temperature of ignition in a close vessel, than to 

 collect these products in separate reservoirs, and to convey one of the products, 

 the inflammable gas, by means of pipes and branching tubes to any required 

 distance, in order to exhibit it there at the orifice of the conducting tube, so 

 that it may be used as a candle or lamp. 



The whole difference between the greater process of the gas-light operation 

 and the miniature operation of a candle or lamp, consists in having the distil- 

 latory apparatus at the gas-light manufactory, at a distance, instead of being 



