268 MB. JOHN LEIGH ON THE CHEMICAL CHANGES 



quired 4^ volumes of oxygen for combustion ; subsequently 

 I found that, \«^hen richer cannels were used, the conden- 

 sible gases required a still larger proportion of oxygen for 

 combustion. The fact, that a greater amount of carbonic 

 acid is produced on exploding the gas with oxygen, than 

 would proceed from a body of the series C„ H^ shows that 

 some other hydro-carbon, the carbon in which exists in a 

 greater ratio to the hydrogen than in this series, is to be 

 found in coal gas. 



When the number of atoms of carbon, in a compound, 

 exceed those of the hydrogen, they are, within certain 

 limits, liquid ; beyond those limits, solid ; thus benzole — car- 

 bon 12, hydrogen 6, in which the carbon is double the hydro- 

 gen ; toluol — carbon 1 4, hydrogen 8 ; and cumol — carbon 

 18, hydrogen 12, are liquid. Whilst naphthaline — carbon 

 20, hydrogen 8; paranaphthaline — carbon 30, hydrogen 12; 

 pyren — carbon 15, hydrogen 3; and chrysen— carbon 12, 

 hydrogen 4, are solid. It may be safely asserted, that 

 where the carbon and hydrogen exist in an equal number of 

 atoms, the compound will be gaseous, unless a very large 

 number enter into the combination. 



Let us now see what arc the practical inferences to be 

 drawn from the preceding postulatory statements. In the 

 first place it will be manifest, that the greater the quantity 

 of hydrogen, and the less oxygen and sulphur a cannel or 

 coal may contain, the better it will be for gas-making; 

 for the two latter rob the coal of a portion of its hydrogen, 

 which is thereby prevented from uniting with a portion of 

 carbon for the production of an illuminating gas. 



The coal should be selected as free from iron pyrites and 

 sulphate of lime as possible, and lumps or masses of 

 these should be thrown out, as they often occur in such a 

 form in the coal. The coal should be moderately dry be- 

 fore being used, which can only be secured by being stacked 

 under cover, otherwise the rain would keep it saturated with 



