The product is water-gas which burns with a non-luminous flame and has no smell. For illuminating purposes it is enriched with vaporised paraffin oil, which gives it a high illuminating power, and a smell rather like that of coal-gas. In some towns as much as 60 per cent. of this carburetted water-gas is mixed with 40 per cent. of coal-gas. Now as the former contains about 30 per cent. of carbonic oxide, and the latter only 7 per cent., a mixture of equal parts of the two gases would contain 18·5 per cent. of carbonic oxide, and would therefore be much more dangerous than coal-gas. This has been found to be so in actual experience of escapes of gas. In speaking of these products of different illuminants, it is necessary to adopt a =standard of light=. In this country the standard has hitherto been a light known as “one-candle power” which is given by a sperm candle burning 120 grains per hour, or in V. Harcourt’s standard flame by a mixture of air and pentane (C₅H₁₂). A good fish-tail or bat’s wing burner for coal-gas gives an illuminating power equal to 16 candles, and burns from 4 to 5 cubic feet of gas per hour. Most flat flame burners known as 4 or 5, and supposed to burn that number of cubic feet of gas per hour, really consume nearly double this amount of gas. In the following table the amount of various products produced and of vitiation of air caused by various forms of illuminants is compared, when an illumination equal to 16 candles is produced in each instance:— ┌────────────────────┬───────────┬─────────┬─────────┬─────────┬─────────┐ │ │ │CARBONIC │ │ │AMOUNT OF│ │ │ AMOUNT │ ACID │MOISTURE │ OXYGEN │VITIATION│ │ │ BURNT. │PRODUCED.│PRODUCED.│ REMOVED.│PRODUCED[a]│ ├────────────────────┼───────────┼─────────┼─────────┼─────────┼─────────┐ │_Sperm candles_ │1740 grains│6·6 c.ft.│ 6·6 c.ft│9·6 c.ft.│ 11 │ │_Paraffin oil_ │992 „ │4·5 „ │ 3·5 „ │ 6·2 „ │ 7 │ │_Coal gas burned in │ │ │ │ │ │ │ Argand burner │4·8 c. ft. │2·5 „ │ 6·4 „ │ 5·8 „ │ 4 │ │ Flat-flame burner_│5·5 „ │3·5 „ │ 7·4 „ │ 6·5 „ │ 6 │ └────────────────────┴───────────┴─────────┴─────────┴─────────┴─────────┘ [a] Stated in terms of the number of adults who would cause an equal vitiation. Thus as an adult expires 0·6 cubic feet of carbonic acid per hour, it follows that the amount of carbonic acid produced in one hour by the various illuminants named in the above table, burning so as to give a light equal to 16 standard candles, varies from 4 to 11 times the amount produced by the adult. Candle and oils possess the advantage over coal-gas that no sulphurous acid is produced in combustion. If the pressure in the mains is excessive, some gas may escape through the burner unburnt or carbonic oxide may escape.