118 MODERN SCIENCE READER 



carbonized, and then were also set up those reactions that 

 produced what we term the bituminous quality. There is 

 no bitumen in coal, but what we mean by bituminous is 

 known to all. Some coal was so much heated that its 

 hydrocarbonaceous matter was driven off to be absorbed in 

 other rocks, such as certain clay shales, or it escaped to the 

 surface and was lost. Thus possibly the Welsh coal was 

 formed with its short flaming qualities that earn for it the 

 term "smokeless," because, though not smokeless in all cir- 

 cumstances, it can be burned without smoke if any simple 

 precautions are taken. Exposed to still greater heat or 

 pressure or both almost all the hydrogenous matter is 

 driven off and the coal is converted into anthracite, a flinty 

 hard variety of carbon. 



If samples of coal be examined their composition cannot 

 be regarded as so different as is their behavior. There is 

 a substance found in parts of the West Indies which re- 

 sembles anthracite in appearance, but it is plastic brittle. 

 It is said not to contain more than one per cent, of hydro- 

 gen to ninety-nine of carbon. Yet this one per cent, 

 entirely changes the nature of the carbon, producing a 

 smoky fuel and the capacity of becoming soft with but a 

 moderate heat. Ordinary bituminous coal contains very 

 much more hydrogen but does not soften at the same low 

 temperature, and when it is exposed to heat it softens in 

 spots and gives off tar vapors. Nothing is known really of 

 the chemical composition of coal. It can be found out easily 

 and with close accuracy just how much hydrogen, how 

 much carbon, oxygen or sulphur a piece of coal does con- 

 tain, but how the atoms of these elements are joined to- 

 gether seems quite beyond finding out at the present time. 

 Thus, if a piece of coal be exposed to distillation in a retort 

 and the different things collected that are produced, there 

 will be found tar, creosote, carbolic acid, cresylic acid, 

 hydrogen, various light and heavy hydrocarbon gases, and 

 so much water and ammonia. But it cannot be said these 

 substances are present in the coal. They have simply been 



