THEORY OF THE COMBUSTION OF COAL IN ELUCIDATION OF THE NATURE OF GAS- LIGHT. 49. Natural history of pit-coal.--Immediate constituent parts of coal.-- Their relative quantities--are different in different kinds of coal.-- Phenomena, which happen during the combustion of coal.--Analysis of coal by distillation.--Great waste of matter capable of producing light and heat, in the usual mode of burning coal.--Proofs of this statement.--Theory of the production of gas-light, compared with the production of light obtained by candles and lamps.--Place which the discovery of lighting with gas occupies in the philosophical order of knowledge. HISTORICAL SKETCH OF THE RISE AND PROGRESS OF THE APPLICATION OF COAL- GAS AS A SUBSTITUTE FOR PROCURING ARTIFICIAL LIGHT. 55. The discovery of the inflammable nature and application of coal-gas for the production of artificial light, cannot be claimed by any body now living.--Early notices of the inflammable property of the gas obtained by distilling coal.--Attempts to substitute it for tallow and oil.--Experiments made with coal-gas by Dr. CLAYTON, Dr. HALES, and the Bishop of Llandaff.--First successful attempt of lighting manu- factories with gas.--_Creditor_ and _debtor_ account concerning the expence of this mode of illumination, when compared with the light obtained by tallow candles.--Claims of Mr. MURDOCH with regard to the economical application of coal-gas.--Claims of Mr. WINSOR.--Experi- ments of Mr. NORTHERN, Mr. CLEGG, Mr. COOK, Mr. ACKERMANN.--Economical statements of the gas-light illumination when compared with the cost of the same quantity of light obtained by means of candles and lamps. THEORY OF THE PRODUCTION OF GAS-LIGHT; AND DESCRIPTION OF A PORTABLE APPARATUS FOR ILLUSTRATING, IN THE SMALL WAY, THE GENERAL NATURE OF THE NEW SYSTEM OF PROCURING LIGHT. 77. Philosophy of the production of coal-gas.--Characters of the various products which the gas-light process affords, their quantities, and modes of obtaining them.--Quantity of gas obtainable from a given weight of coal.--Illuminating power of a given bulk of coal-gas compared with the illuminating power of a given weight of tallow candles.--Practical directions with regard to the production of the gas from coal.--Its chemical constitution and analysis.--Pit-coal is not the only substance which affords carburetted hidrogen gas.--This gas exists ready formed in nature.--Mode of collecting it when found native.--Is given out by all kinds of vegetable matter, submitted to distillation in close vessels.--Other sources of obtaining this gazeous fluid.--Practical directions with regard to the method of obtaining from coal, this gazeous substance, as best suited for illumination.--Chemical constitution of coal-gas.--How ascertained.