LIGHTING. 



and carbonic acid have still to be removed. 

 To remove the ammonia, the washer or the 

 scrubber is used. In the washer, the gas is 

 forced to pass through water to a depth of 

 several inches, or through a solution containing 

 an ingredient with which the ammonia will com- 

 bine. The scrubber, which may be used instead 

 of the washer, is an upright vessel, in which the 

 gas is made to pass through brushwood, or layers 

 of small stones, or coke, through which water may 

 be made to percolate. 



There are two kinds of purifiers the wet and 

 the dry. Either may be used separately, or they 

 may be used in succession. Lime is the purifying 

 material which is most effective ; a preparation of 

 the oxide of iron, however, is rapidly coming into 

 general use. Lime is used in the wet purifier in 

 the form of cream of lime, through which the gas 

 is made to pass. The dry purifier is a square or 

 oblong vessel containing a series of perforated 

 trays, on each of which a layer of dry slaked lime 

 is spread. The lime absorbs the sulphuretted 

 hydrogen, a portion of the ammonia, and the car- 

 bonic acid. When saturated, it is removed, and 

 the vessel is refilled with fresh material. The re- 

 fuse lime is extensively used as a manure. When 

 the oxide of iron is employed as the purifying 

 material, the preparation is spread in the same 

 manner as the lime, but to a much greater thick- 

 ness. When, by the absorption of sulphuretted 

 hydrogen, the oxide of iron has become sulphuret 

 of iron, it is taken out, and by exposure to the 

 atmosphere, it is reconverted into oxide, and can 

 be used again and again. After passing the puri- 

 fier, the gas, now fit for use, is measured by the 

 station-meter, and conveyed to the gas-holder. 



The gas-holder is an inverted cylindrical vessel 

 of sheet-iron, placed in a tank of cast-iron, stone, 

 or brick, filled with water. A pipe ascends from 

 the bottom of the tank through the water, to admit 

 the gas to the space between the surface of the 

 water and the crown of the gas-holder. Another 

 pipe descends through the water and the bottom 

 of the tank, for the issue of the gas to the main- 

 pipe. The water is for the purpose of retaining 

 the gas within the vessel. The pressure or force 

 imparted to the stream of ' gas issuing from the 

 retorts and exhauster, raises the gas-holder, and the 

 weight of the gas-holder, or such part of it as is 

 not taken off by balance-weights, impels the gas 

 through the pipes. Gas-holders are constructed 

 of all sizes up to 200 feet in diameter, and are 

 made to contain quantities up to two and a half 

 millions of cubic feet. In large establishments, 

 telescopic gas-holders are used, and economy 

 of space and cost is thereby effected two con- 

 centric gas-holders being contained in one tank. 

 Before reaching the main-pipes, the pressure 

 of the gas is regulated by the governor, which 

 acts like that of the steam-engine. 



Distribution of Gas. 



The distribution of the gas from the gas-holder 

 is effected in cast-iron pipes called mains ; the 

 pipes branching from the. mains to supply gas to 

 dwelling-houses or manufactories are called 

 service-pipes. The pipes have, or should have, 

 an inclination to the main, and the main itself 

 should incline towards the gas-work. For watery 

 vapour is present in small quantity in the gas ; 

 being condensed into water in the pipes, it natu- 



rally collects in the lowest part, and at last inter- 

 rupts the continuous flow of gas, so as to cause a 

 flickering of the flame in the burners. Where the 

 proper inclination cannot be attained, an entrap- 

 ping box or vessel is placed at the part where 

 liquid is apt to collect, so that it can be removed 

 from time to time as it accumulates. 



The quantity of gas charged for by gas-com- 

 panies was at one time regulated by the number 

 and kind of burners employed, and the time they 

 were allowed to burn, and this is still the case 

 as regards the lighting of streets ; but this was 

 found to be a most uncertain and unsatisfactory 

 method of guessing the consumption by any indi- 

 vidual. It is now obviated by the use of meters, 

 of which there are two kinds, the wet and the dry. 

 The wet-meter consists of a hollow case of iron, 

 containing an inner cylinder or drum, so con- 

 structed, that the gas passing through it, by the 

 pressure it receives at the gas-work, causes it to 

 revolve on an axis ; each revolution allows a 

 known quantity of gas to pass through the water, 

 with which the outer vessel is partially filled, to 

 the exit-pipe ; and as the revolutions are regis- 

 tered by wheel-work and an index, the quantity of 

 gas consumed is indicated with considerable 

 accuracy. The gas-company charges the con- 

 sumer according to the quantity indicated. This 

 meter is, however, liable to have the water frozen 

 in severe weather, and requires to be frequently 

 replenished with water. To remedy this, various 

 ' dry-meters ' have been contrived, but none have 

 yet come into general use. 



Burning of Gas. 



There is one important fact in the burning of 

 gas, which is equally true of animal and vegetable 

 oils. When a given quantity is burnt in a large 

 flame, a greater amount of light is obtained than 

 when the same quantity is burnt in a smaller 

 flame. Hence one large lamp or gas-jet is better 

 than three or four burning the same quantity in the 

 same time. The cause of this becomes apparent 

 by considering what takes place when a jet of gas 

 is turned down to the lowest point. Here the 

 white light altogether disappears, and only a blue 

 flame remains ; the small body of gas as it issues 

 becomes mixed and diluted with air, and the whole 

 is perfectly consumed, as in the Bunsen burner, 

 without any of the carbon becoming solid and 

 incandescent. On gradually admitting more gas, 

 a white speck first appears in the middle of the 

 blue, and this speck the area of imperfect com- 

 bustion goes on increasing not only in absolute 

 size, but its proportion to the area of perfect com- 

 bustion becomes greater as the whole flame is 

 enlarged. The limit to this economy is the 

 quantity that can be burnt without smoke. This 

 difference between large and small flames does 

 not hold in burning paraffin oil 



The gas-burners most used are the single coni- 

 cal jet, the bat-wing, and the union or fish-tail jet. 

 In the bat-wing, the gas issues from a slit across 

 the head of the burner. The union-burner is 

 pierced with two holes, so that the two streams of 

 gas impinge on each other, and produce a flat 

 flame. Metal burners are exceedingly liable to 

 rust, and become useless ; but there is a patent 

 burner, made of a silicious composition, which 

 lasts for years without deterioration. 



Bude Burner Bude Light. The Bude burner 



4W 



