PLANT'S GROWTH AND DECAY 111 



coal out of contact with air. The portion which under 

 these conditions escapes, and may therefore be termed the 

 volatile matter, consists of various compounds of carbon 

 and hydrogen and other more complex bodies containing 

 not only these elements, but also the oxygen and nitrogen 

 present in the coal. 



The proportion of volatile matter present, consisting as 

 it does largely of hydrocarbons, makes a wonderful differ- 

 ence in the way in which a coal burns, the presence of 

 hydrogen and lower members of the hydrocarbon series 

 giving the coal ease of ignition and the property of burning 

 with flame, while the more complex hydrocarbons and 

 organic bodies render the flame so produced heavy and 

 smoky in its character. If a coal which contains a very 

 small percentage of volatile matter, such as anthracite, be 

 taken, it is found difficult to ignite and almost impossible 

 to burn without specially arranged conditions of draft, 

 while the more bituminous coals, such as cannel, can be 

 ignited by the flame of a match, and will burn with the 

 greatest ease. 



With the increase in bituminous matter in the coal, the 

 fixed carbon or coke left on distillation naturally decreases 

 in quantity, and coals are generally classified on the basis 

 of the amount of fixed carbon they contain, into lignites, 

 cannels, bituminous coal, steam coal or semi-bituminous 

 coal, and anthracite, the percentage of carbon varying from 

 sixty-five per cent, in some lignites up to over ninety per 

 cent, in the anthracites. The relation existing between the 

 composition of the coal and its powers of smoke production 

 is one that will have to be discussed again in considering 

 the fitness of fuels for the class of work they have to 

 perform. 



Any form of bituminous coal when subjected to a raised 

 temperature begins to yield products of a liquid and gas- 

 eous character ; and if the temperature be kept at the lowest 

 point at which any action can take place, the liquid distil- 

 lates formed are of an oily character and not greatly dis- 



