GAS MANUFACTURE AND GAS COMPANIES. 481 



is not mixed with the water-gas until the latter has been purified ; in 

 others the petroleum is added directly to the coal. Anthracite coal, 

 only, is used in the manufacture of water-gas, and great care is neces- 

 sary to keep the temperature up to a white heat, since, if it falls too 

 low, a large proportion of carbonic acid will be formed, and will 

 injure the illuminating power of the gas unless it is removed by 

 purification. Anthracite coal contains sulphur, and yields ammonia 

 when distilled, so that purification is as necessary for water as for 

 coal-gas, and therefore no saving is made in this respect. The real 

 saving is in coal, since a large volume of steam can be decomposed by 

 one ton. 



It is necessary now to make a more particular inquiry into the 

 nature of the different gases and compare them with each other. Coal- 

 gas in its salable condition is composed about as follows : 



NAMES. 



Hydrogen 



Marsh-gas 



Carbonic oxide 



Olefiant and other hydrocarbons 



Nitrogen 



Oxygen 



Carbonic anhydride 



Steam 



Heidel- 

 berg. 



44.00 



38.00 



5.73 



7.27 

 4.23 



0.37 



Bonn. Chemnitz. 



39.80 



43.12 



4.66 



4.75 



4.65 



3.02 



51.29 

 36.45 

 4.45 

 4.91 

 1.41 

 0.41 

 1.08 



London, 

 Common. 



46.00 



39.50 



7.50 



3.80 



0.50 



0.70 

 2.00 



London, 

 Cannel. 



27.70 

 50.00 



6.80 

 13.00 



0.40 



0.10 

 2.00 



The hydrogen and carbonic oxide burn with anon-luminous flame, 

 and marsh-gas burns with only a slightly-luminous one, the illuminat- 

 ing power coming almost entirely from the olefiant gas and other 

 hydrocarbons. The oxygen, carbonic acid, and nitrogen, being in- 

 combustible, injure the illuminating power very greatly. The oxy- 

 gen and nitrogen are admitted accidentally by the introduction of a 

 little air in charging the retorts. Hence, other things being equal 

 the illuminating power of the gas increases with the proportion of 

 olefiant and other hydrocarbons, and these depend chiefly on the kind 

 of coal used and the temperature at which it is carbonized. The gas- 

 coals are the bituminous caking coals and cannel. The bituminous 

 shales, like the boghead mineral of Scotland, and asphalt mine'rals, like 

 the Albertite of Nova Scotia and the Grahamite of West Virginia, 

 are used in small quantities for enriching. The yield of good gas- 

 coal, like the Penn, is about 10,000 cubic feet of 15 to 16 candle- 

 power gas to the ton (2,240 lbs.). The enriching coals yield a larger 

 amount of richer gas, and the asphalt minerals from 13,000 to 15,000 

 cubic feet of 30 to 50 candle-power. The relative cost of enriching with 

 these or with naphtha is a very important question. In a number of 

 experiments made at the Boston Gaslight Works, for the purpose of 

 testing the value of Albertite as an enricher, it was found that the 



VOL. x. 31 



