GAS, MANUFACTURE OK. 



OAS, MANUFACTURE OF. 



I - 



never below 45'). After lairing tli* condensers, the gas sometimes 

 into the icnMtrt, which usually consist of srries of shrives 



ooTered with screened porous coke ; and the gag, passing through these 

 materials, and being in its passage exposed to the action of a stream of 

 water filtering constantly through the coke, parta with the remaining 

 portion of its tar and a considerable portion of the ammonia it holds in 

 solution. In large works, what is called a mother is often used instead 

 of a scrubber, and in it the gas is made to pass through a solution of 

 muriate of manganese, whose action upon the ammonia is the same as, 

 or even more effectual than, that of the scrubber. From thence the gas 

 passes into the purijiert, where the sulphuretted hydrogen, and many of 

 the remaining ammoniacal elements it may contain, are eliminated, BO 

 that on leaving the purifiers the gas is fit to be passed through the 

 Italian-meter into the gcu-holderi in a state adapted for household con- 

 sumption. As a general rule, the exposed surface of the condensers 

 should be in the proportion of 150 feet superficial to every 1000 feet of 

 gas operated upon ; but every description of coal will require a special 

 treatment in this respect ; because the more highly bituminous coals, 

 for instance, part with the tarry matters volatilised in the retorta with 

 more difficulty than do the ordinary coals ; and it is desirable to retain 

 a* much a* possible of those matters, provided that they be not 

 exposed to deposition at any time in the course of their passage 

 through the distributing mains. 



When the gas leavea the condensers it usually contains impurities, 

 consisting of about 1} parts of ammonia, 8 parts of sulphuretted 

 hydrogen, and 25 parta of carbonic acid in every 1000 measures of 

 the gas, according to the author of the very remarkable papers on the 

 ' Chemistry of Coal Gas,' inserted in the 2nd and 3rd vols. of the 

 ' Journal of Gas Lighting.' For the purpose of removing these im- 

 purities it would appear that the most theoretically perfect course 

 would be to pass the gas, firstly, through either the sulphate, or the 

 muriate of lime, and then to pass it through the pure hydrated lime 

 in powder. It happens, however, that some of the impurities which 

 are retained by these forms of lime, namely, the hydro-sulphate of 

 ammonia, and the hydro-sulphate of lime, are either extremely volatile, 

 or are susceptible of decomposition on exposure to the air ; anil muter 

 such circumstances their removal from the purifiers, when the lime 

 iteelf has been saturated, give* rise to so great a nuisance that in 

 crowded district*, or in the centre of towns, it is necessary to employ 

 some other material than lime as the basis of the purification. It is 

 for thw purpose that metallic salts have lately been introduced ; and 

 in come of the most scientifically managed work* (as at Liverpool for 

 instance), tht process adopted within a very recent period, has been 

 described as being as follows: "Common green copperas (sulphate of 

 iron) is put into a mill, a little water being added to make it into a pasty 

 mass. Slaked lime is then added, in the proportions of one part of limu 

 to two of copperas, with water sufficient to make the whole, when 

 ground together, of tho consistency of a stiff paste. In this state it is 

 removed, an-1 cut into pieces with a spade, and as it dries it forms a 

 powder which consist* of sulphate of lime and hydrated sesquinoxide 

 of iron. The powder, after being sifted is put into the purifier, 

 where the oxide of iron becomes reconverted into sulphuret of iron; 

 and that again by exposure to the air becomes reconverted into oxide 

 of iron with a deposition of sulphur in the man. This process is 

 repeated about 28 times, and then it is found, that owing to the 

 accumulation of sulphur, the same material cannot again be put into 



the purifier. In this sUte the material is routed in an oven, the 

 sulphur being in the tint instance distilled from the mass, and 

 collected in a separate form; and during the roasting process, the 

 iron becomes red hot, and is rendered anhydrous. When taken out 

 f the ovens the iron is thrown into open yards to cool ; and is then 

 moistened with water, in order to reconvert it into the hydroux 

 and again put into the purifiers to commence a fresh auocession of 

 repeated actions." In the majority of the London works saw-dust u 

 mixed with the oxide of iron to increase its active surface ; and in 

 some cases the gas U made to pan through the muriate of manganese 

 before passing through the iron, whilst in others it is passed through 

 dry lime purifiers after leaving the iron, because the action of tho 

 latter material is not sufficiently energetic to remove all the ammonia, 

 nor does it materially affect the carbonic acid, in it* various forms of 



. .-.-. 



The lime used for the purification of gas should bo of the purest 

 and richest description, such in fact as would be obtained by the 

 calcination of chalk, or of crystalline carbonates of lime, and which 

 expands in volume very considerably when slaked. It should be kept 

 in store in lumps, but ground before being used, and mixed with a 

 sufficient quantity of water to bring it into a stiff plastic state ; and in 

 that state it must be spread upon the screens of the purifiers in an 

 even sheet of, at Ike moil, 24 inches in thickness. The successful 

 working of the lime depends, it may be observed, on ^he evenness of 

 the layer ; but the most economical condition for its use is that it 

 r-hmil.l expose a large surface to the gas passing through. (Jem-rally 

 s|>eaking, it is calculated that one bushel of ground dry lime will v- hen 

 slaked, spread over a surface of 25 superficial feet, and suffice for the 

 purification of 10,000 cubic feet of Newcastle coal gas. In the oxide 

 of iron purification, a greater surface U required than when lime only 

 ia used ; but the proportion usually adopted is to make the area of the 

 purifiers such that they should present a surface of one superficial foot 

 to every 150 cubic feet of gas they are intended to pass; and the 

 diameter of the connecting pipes is made in inches, equal to the square 

 root of the area of the purifiers in feet superficial The use of wet 

 lime purifiers is now so universally abandoned, that it is not worth while 

 to enter into a description of the mode of forming or of working them. 



One of the most important duties of the manager of a gas factory U 

 to ascertain that his purifiers operate successfully, and for this purpose 

 he should frequently test the gas by means of paper, prepared by 

 being steeped in a solution of acetate of lead in distilled water, one of 

 the best tests for sulphuretted hydrogen. The papers should not be 

 changed in colour by contact with the gas in the lost of the series of 

 purifiers. Sometimes papers steeped in a solution of the nitrate of 

 silver are used as testa of the purity of gas from sulphuretted 

 hydrogen. Test papers of litmus are used to detect ammonia, or 

 carbonic oxide. 



It may bo as well here to add that the order In which the gas is 

 made to pass through the purifier and the scrubber, is frequently the 

 reverse of the one described above ; and in small works the use of the 

 scrubber is often entirely dispensed with. 



8. The first operation which it is desirable to adopt in the storeage 

 of gas, is to pass it through the station meter, in order to be able to 

 control the working of the retort house, and to check roughly the con- 

 sumption in the mains and the private distribution. For the former 

 purpose it is necessary that the wheel-work of the meter should carry 

 a " 1. 11- tale," by means of which the passage of the gas is recorded in 

 such a manner as to allow the rate of working, hour by hour, to be 

 identified. The value of the station meter, as a check upon the actual 

 consumption, must vary in a marked degree with the circumstances of 

 the localities, and the mode of manufacture ; for the rate of leakage, 

 and the amount of condensation, which may take place after the gas 

 >.|iiiul<l have passed the meter, differ in almost every town. It is, 

 however, by no means rare to find that the loss, known in gas-working 

 accounts, under the name of " unaccounted for gas," amounts to as 

 much as 20 per cent, of the total quantity passing through the station 

 meter; and the efforts of the superintendent must be earnestly 

 directed to reducing it to a minimum. Kven if a |x>rtion of the loss 

 be attributable to the condensation of the bolder and pipes, it argues 

 an unsatisfactory state of working; for the temperature of the gas 

 ought to have been lowered, before it was paused into the purifiers, 

 to such a point as to render any subsequent condensation impossible 

 unless in intensely cold weather. 



