PRINCIPLES OF CHEMISTRY 



The nature of the phenomenon, and the products arising from it, are 

 the same as those produced by heating alone, as that part which is in a 

 state of combustion serves to heat the remainder of the fuel. The decom- 

 position which takes place on heating a compound composed of carbon, 

 hydrogen, and oxygen is as follows : A part of the hydrogen is sepa- 

 rated in a gaseous state, another part in combination with oxygen, 

 and a third part separates in combination with carbon, and sometimes in 

 combination with carbon and oxygen in the form of gaseous or volatile 

 products, or, as they are also called, the products of dry distillation. 

 If the vapours of these products are passed through a highly-heated 

 tube, then they are changed again in a .similar manner, and finally 

 resolve themselves into hydrogen and charcoal. All these various pro- 

 ducts of decomposition contain a smaller amount of carbon than the 

 primary organic matter ; part of the carbon separates in combination 

 with hydrogen and oxygen, but part of it remains in a free state, form- 

 ing charcoal. 3 It remains in that space where the decomposition takes 



-moke (Chapter IX.) which burns, emitting much heat. In works and factories where 

 lari:c quantities of fuel are consumed, many appliances are adopted to ensure perfect com- 

 bustion, and to combat against such a ruinous practice as the imperfect combustion of 

 fuel. The most effective and radical means consists in employing the combustible gases 

 i regenerative and water gases), because by their aid perfect combustion can be easily 

 realised without a loss of heat-producing power and tl'i> highest temperature can 

 be reached. When solid fuel is used (such as coal, wood, and turf), imperfect combustion 

 is most liable to occur when the furnace doors are opened for the introduction of fresh 

 fuel. The step furnace may often prove a remedy for this defect. In the ordinary 

 furnace fresh fuel is placed on the burning fuel, and the products of dry distillation of 

 the fresh fuel have to burn at the expense of the oxygen remaining uncombined with 

 the burnt fuel. Imperfect combustion is observed in this case also from the fact that 

 the dry distillation and evaporation of the water of the fresh fuel lying on the top of that 

 burnt, lowers the temperature of the flame, because part of the heat becomes latent. 

 On this account a large, amount of smoke (imperfect combustion) is observed when a fresh 

 quantity of fuel is introduced into the. furnace'. This may be obviated by constructing 

 the fill-mice (or managing the stoking] in such a way that the products of distillation pass 

 through the red-hot charcoal lemaining from the burnt fuel. It is only necessary in 

 order to ensure this to allow a. sufficient quantity of air for perfect combustion. All this 

 may lie easily attained by the use of step fire-liars. The fuel is shovelled into a funnel 

 and falls on to the fire-bars, which are disposed in the form of a staircase. h burning 

 charcoal is below, and therefore, the flame formed by the fresh fuel is heated by the con- 

 tact of the red-hot, burning charcoal. An air supply through the lire grate, and its equal 

 distribution on the fire-bars (otherwise the air will blow through the empty space and 

 lower the temperature i, a proper proportion between the supply of air and the chimney 

 draught, and a perfect admixture of air with the flame (without an undue excess of air), 

 ire the means by which we can strive against the imperfect combustion of such kinds of 

 fuel as wood, peat, and ordinary (smoky) coal. Coke, steam coal, anthracite, burn with- 

 out smoke, because they do not contain hydrogenous substances which furnish the pro- 

 ducts, of drv distillation, but imperfect combustion may occur with them also; then the 

 smoke contains carbonic oxide. 



"' The various kinds of coal used in practice and found in nature are the products of 

 the transmutation of the remains of organic matter. There is no organic substance 

 which contains in itself sufficient oxvgen not onlv to combine with hydrogen in order to 



