102 



GAS-LIGHTING 



chambers ; each chamber is divided into two by 

 a diaphragm, which may be displaced to one side 

 or the other. The gas is admitted to the one side 

 of this diaphragm until it is displaced to the full 

 extent of its range ; when this occurs the gas 

 is admitted to its other side, and the gas pre- 

 viously admitted is allowed to go on to the burner, 

 and so on alternately. The chambers act alter- 

 nately, thus passing the dead-points. The dia- 

 phragms are connected with wheel work which record 

 their successive oscillations, and represent on the 

 dials the corresponding number of cubic feet passed 

 through the apparatus. By an act of parliament 

 ( 1859) all gas-meters must register not more than 



2 per cent, in favour of the seller and not more than 



3 per cent, in favour of the purchaser of gas ; and 

 meters must bear the seal of an inspector appointed 

 under the act. Meters have recently been intro- 

 duced which enable the poorer consumer to purchase 

 gas by pennyworths on the familiar ' penny in a slot' 

 principle ('coin' meters), or to pay into the meter 

 a definite sum which will allow the mechanism to 

 transmit the prearranged quantity of gas ('stop' 

 meters). In Brussels the gas. burned by day and 

 that used at night were for some years registered 

 on different dials of the same meter. 



The lighting-power of a gas is measured in 

 terms of the number of candles to which a 5-feet 

 standard flat-flame is equivalent. The lighting 

 value of a gas is measured by the number of 

 candle-hours it will yield per 1000 cubic feet 

 when burned in standard burners ; thus 1000 

 cubic feet of 20-candle gas will keep up a light of 

 20 candles for 200 hours (using 5 cubic feet per 

 hour), and its lighting value is 4000 candle-hours, 

 or, as it is generally abbreviated, 4000 'candles.' 

 Since a standard candle shines for one hour at the 

 expense of 120 grains of sperm consumed, the 

 lighting value of a gas is frequently stated as so 

 many grains of sperm ; thus the 'sperm value' of 

 20-candle gas is 20 X 200 X 120 = 48,000 grains 

 per 1000 cubic feet. During recent years cannel 

 coal has become too expensive to make gas 

 from, and the use of cannel gas has been 

 given up in the limited region of the west end 

 of London to which it was formerly supplied. 

 Gas - makers have, therefore, had to reduce 

 their standard, as in Edinburgh, where the 

 28-candle gas has been replaced by 24-candle 

 gas, or else to turn their attention to the enrich- 

 ment of a poorer gas made from ordinary coal. 

 This enrichment is effected by the addition of 

 hydrocarbon vapours in various forms to the poorer 

 coal-gas. If gas of higher quality be made by a 

 more costly process, so that it costs say d l pence per 

 1000 cubic feet to make gas of a lighting-power C 1 , 

 instead of d pence to make gas of a lighting-power 

 (7, the cost per additional candle of lighting-power 

 is { (d l - d) -f- ( C 1 - C ) } pence per 1000 cubic feet of 

 gas made. If the enriching gas be added in the 

 proportion of/" cubic feet to 1000 of coal-gas, of a 

 lighting value of C candle-hours per 5 cubic feet, 

 then if the resulting (1000+/) cubic feet of en- 

 riched gas have a lighting value of C 1 candle-hours 

 per 5 cubic feet, and if the original gas and the 

 added enriching gas respectively cost d and d 1 pence 

 per 1000 cubic feet, the additional cost per lOOOcubic 

 feetof gas made is {/(d l -d) * [( 1000 -f /) (C 1 - C)]} 

 pence per additional candle of lighting-power. If 

 we add a richer gas to a poorer, the lighting-power 

 of the mixture is generally not equal to the arith- 

 metical mean as deduced by calculation ; there is 

 generally deterioration due to dilution ; but it 

 often happens that if we add a little poor gas to an 

 exceedingly rich one the lighting-power is higher 

 than we would have expected. But if we apply to 

 the actual results of enrichment the same methods 

 which we would use if there had been no deteriora- 



tion, we obtain a useful nominal value for the light- 

 ing-power of the richer gas, which is called its 

 ' enrichment value.' Thus if we mix 13% cubic feet 

 of oil-gas, of an unknown enrichment value C n , 

 with 1000 cubic feet of 14-candle coal-gas, and 

 obtain 1013% cubic feet of 15-candle gas, we find, 

 from the equation 1013% X 15 = ( 1000 X .14) + 13% C u , 

 that C' 11 = 90 candles, the nominal lighting-power 

 of the enriching gas, or its enrichment value. 

 As means of enrichment by mere admixture, we 

 have benzol-vapour, which is much used on the 

 Continent, and which for small enrichment adds 

 about 4700 candle-hours per gallon of benzol 

 evaporated into the gas ; carburine or light petro- 

 leum oil (practically hexane, CeHu), used to some 

 extent in London under the Maxim patents, and 

 adding about 1600 candle-hours per gallon evap- 

 orated ; and oil-gas. Oil has also been employed 

 as spray injected into the coal-retorts themselves ; 

 and coal-gas is largely carburetted by being 

 exposed, along with the vapours obtained by the 

 distillation of oil, to a high temperature, so that 

 these vapours maybe rendered more 'permanent,' 

 or less liable to condense in transit through the 

 pipes. 



It is of great importance that in the first place 

 gasfittings should be adequate to supply the 

 maximum demand for gas ; and in the second, that 

 the gas should emerge from each burner under a 

 low pressure. If the gasfittings pipes, &c. be 

 inadequate, as they mostly are, full flames cannot 

 be produced, and the light is unsatisfactory ; if, on 

 the other hand, the full pressure of the mains is 

 communicated too directly to the gas-burners them- 

 selves, there is a tendency to flare. This can be 

 mitigated by partially turning off at the meter ; 

 but even then the variable demand may result in 

 variable pressures at the burners. There should be 

 a governor for each gas-burner, or for each small 

 group of gas-burners ; these are now readily pro- 

 curable, and when they are used a full flame is 

 obtained which is constantly and steadily kept up 

 by a comparatively slow supply of gas ; the incan- 

 descent particles or heavy heated hydrocarbon 

 vapours upon which luminosity depends are 

 allowed to remain as long as possible in the 

 flame, and the gas is thoroughly burned ; and air 

 is not swirled into the interior of the flame by the 

 swift current of gas, thus spoiling the luminosity. 

 An ordinary burner gives greatly superior results 

 when governed ; since the electric light has caused 

 more attention to be paid to the efficient burning 

 of gas, the burners themselves have been greatly 

 improved ; but burners should always be selected 

 with reference to the quality of gas to be used in 

 them. 



The ordinary ratstail burner has long given place 

 to the batswi'iig and fishtail burners, the former 

 of which are made with a clean slit across the 

 head of the burner ; the latter have two passages 

 converging towards one another, the result being 

 that the two streams of gas meet one another 

 and spread out into a flat sheet of flame. The 

 former use much gas at ordinary pressures, and a 

 very small pressure (%-inch of water just below the 

 burner) is sufficient to bring out the full lighting- 

 power. In hollow-top burners the pressure is 

 relieved by the gas swirling in a cavity below the 

 outlet-slit. Burners of these classes should always 

 be selected with steatite tops ; metal burners soon 

 rust and spoil the flame. In Argand burners the 

 gas issues through a ring of holes ; the flame is 

 tubular, and is surrounded by a chimney; air 

 ascends both inside and outside the tubular flame. 

 In Dumas burners the circle of holes is replaced by 

 a circular slit, and a regulator controls the admis- 

 sion of air. These various burners have also been 

 collected in groups to form the so-called sunlights, 



