August 24, 1 882 J 



NATURE 



595 



'resent, we find from a Government return that the capital in 

 ested in gasworks in England, other than those cf local author- 

 ties, amounts to 30,000,000/. ; in these 4,281,048 tons of coal 

 are converted annually, producing 43,000 million cubic feet of 

 gas, and about 2,800,000 tons of coke ; whereas the total 

 amount of coal annually converted in the United Kingdom 

 may be estimated at 9,000,000 tons, and the by-pr..ducts there- 

 from at 500,000 tons of tar, i,coo,ooo tons of ammonia liqu&r, 

 and 4,000,000 tons of coke, according to the returns kindly 

 furnished me by the managers of many of the gasworks and cor- 

 porations. To these may be added say 120,000 tons of sulphur, 

 which up to the present time is a waste product. 



Previous to the year 1856— that is to say, before Mr. W. H. 

 Perkin had invented his practical process, based chiefly upon the 

 theoretical investigations of Hoffman, regarding the coal-tar 

 bases and the chemical constitution of indigo — the value of coal- 

 tar in London w as scarcely a halfpenny a gallon, and in country 

 places gas-makers were glad to give it away. Up to that time 

 the coal-tar indu-try had consisted chiefly in separating the tar 

 by distillation into naphtha, creosote, oils, and pitch. A few 

 distillers, however, made small quantities of benzene, which had 

 been first shown— by Mansfieln, in 184(3 — to exist in coal-tar 

 naphtha mixed with toluene, cumene, &c. The discovery, in 

 1S56, of the mauve or aniline purple gave a great impetus to the 

 coal-iar trade, inasmuch as it in cessitated the separation of large 

 quantities of benzene, or a mixture of benzene and toluene, from 

 the naphtha. The trade w as further increased by the discovery 

 of the magenta or rosaniline dye, which required the same pro- 

 ducts for its preparation. In the meantime, carbolic acid was 

 gradually introduced into commerce, chiefly as a disinfectant, 

 but also for the production of colouring matter. 



The next most important development arose from the dis- 

 covery by Grrcbe and Liebermann tbat alizarine, the colouring 

 principle of the madder root, was allied to anthracene, a hydro- 

 carbon existing in coal-tar. The production of this colouring 

 matter from anthracene followed, and is now one of the most 

 important operations connected with tar distilling. The success 

 of the alizarine made in this manner has been so great that it has 

 almost entirely ;uper f ededthe use of madder, which is now culti- 

 vated to only a comparatively small extent. The most important 

 colouring matters recently introduced are the azo-scarlets. They 

 have called into use the coal-tar hydrocarbons, xylene and 

 cumene. Naphthalene is also used in their preparation. These 

 splendid dyes have replaced cochineal in many of its applica- 

 tions, and have thus seriously interfered w ith its use. The 

 discovery of artificial indigo by Professor Baeyer is of great 

 interest. For the preparation of this colouring matter loluene 

 is required. At pre ent artificial indigo does not compete 

 seriously with the natural product ; but should it eventually be 

 prepared in quantity from toluene, a further stimulus will be 

 given to the coal-tar trsde. 



The colour industry utilises even now practically all ihe ben- 

 zene, alarge proportion of the solvent nap! ha, all the anthracene, 

 and a portion of the napthaline resulting fr'-.m the di> (illation of 

 coal-tar ; and the value of the colouring mat'er thus produced is 

 estimated by Mr. Perkin at 3,350,00c/. 



The demand for ammonia may be taken as unlimited, on 

 account of its high agricultural value as a mat ure ; and, con- 

 sidering the failing supply of guano and the growing necessity 

 for stimulating the fertility of our soil, an increased production 

 of ammonia may be rrgarded as a matter of national in portance, 

 for the supply of which we have to look almost exclusively to 

 our gasworks. The present production of 1,000,000 tons of 

 liquor yields 95,000 tons of sulphate of ammonia ; which, taken 

 at 20/. 10s, a ton, represents an annual value of 1,947,000/. 



The total annual value of the gasworks by-products may 1 e 

 estima'ed as foil iws : — 



Colouring matter ...... .£3,350,000 



Sulphate of ammonia ..... 1,947,000 



Pitch (325,000 tons) 365,000 



Creosote (25,000,000 gallons) . . . 2oS,oco 



Crude carbolic acid (1, ooo.cco gallons). . 100,000 



Gas coke, 4,000,000 tons (after allowing 

 2,000,000 tons con umption in working tie 

 retorts) at 12s. ...... 2,400,000 



Total ^8,370,000 



Taking the coal used, 9,cco,cootons, at \2s., eqnal 5,400,000/., 

 it follows that the by-products exceed in value the coal used by 

 very nearly 3,000,000;. 



In using raw coal for heating purposes these valuable products 

 are not only absolutely lost to us, but in their stead we are 

 favoured with those semi-gaseous by-products in the atmosphere 

 too well known to the denizens of London and other large towns 

 as smoke. Professor Roberts has calculated that the soot in the 

 pall hanging over London on a winter's day amounts to l iifty 

 tons, and that the carbonic oxide, a poi-onous compound, result- 

 ing from the imperfect combustion of coal, may b: taken as at 

 least five times that amount. Mr. Aitken has shown, moreover, 

 in an interesting paper communicated to the Royal Society of 

 Edinburgh, last year, that the fine dust resulting from the imper- 

 fect combustion of coal is mainly instrumental in the formation 

 of fog ; each particle of solid matter attracting to itself aqueous 

 vapour, these globules of fog are rendered particularly tenacious 

 and disagreeable by the presence of tar vapour, another result of 

 imperfect combustion of raw fuel, which might be turned to 

 much better account at the dye-works. The hurtful influence of 

 smoke upon public health, the great personal discomfort to 

 which it gives rise, and the vast expense it indirectly causes 

 through the destruction of our monuments, pictures, furniture, 

 and apparel, are now being recognised, as is evinced by the 

 success of recent Smoke Abatement Exhibitions. The most 

 effectual remedy would resnlt from a general recognition of the 

 fact that wherever smoke is produced, fuel is being consumed 

 wastefully, and that all our calorific effects, from the largest 

 down to the domestic fire, can be realised as completely 

 and more economically, without allowing anv of the fuel 

 employed to reach the atmosphere unburnt. This most desirable 

 result may be effected by the use of gas for all heating purposes 

 with or without the addition of coke or anthracite. 



The cheapest fotm of gas is that obtained through the entire 

 distillation of fuel in such gas producers as are now largely used 

 in working the furnaces of glass, iron, and steel works; but "as 

 of this description would not be available for the supply of 

 towns owing to its bulk, about two-thirds of its volume being 

 nitrogen. The use of water-gas, resulting from the decomposi- 

 tion of steam in passing through a hot chamber filled with coke, 

 has been suggested, but this gas also is objectionable, because it 

 contains, besides hydrogen, the poisonous and inodorous gas 

 carbonic oxide, the intioduction of which into dwelling-houses 

 could not be effected without considerable danger. A more 

 satisfactory mode of supplying beating separately from illumi- 

 nating gas would consist in connecting the retort at different 

 periods of the distillation with two separate systems of mains for 

 the delivery of the respective gases. Experiments made some 

 j ears ago by Mr. Ellisen of the Paris gasworks have shown that 

 the gases rich in carbon, such as defiant and acetylene, are 

 developed chiefly during an interval of time, beginning half an 

 hour after the commencement and terminating at half the whole 

 period of distillation, whilst during the remainder of the time, 

 marsh gas and hydrogen are chiefly developed, which, while 

 possessing little illuminating power are most advantageous for 

 heating purposes, By resorting to improved means of heating 

 the retorts with ga«eous fuel, such as have been in use at the 

 Paris gasworks for a considerable number of years, the length of 

 time for effecting each distillation may be shortened from six 

 hours, the usu 1 period in former years, to four, or even three 

 hours, as now praotised at Glasgow and elsewhere. By this 

 means a given number of retorts can be made to produce, in 

 addition to the former quantity of illuminating gas of superior 

 quality, a similar quantity of heating gas, resulting in a 

 oimimshed cost of production and an increased supply of the 

 valuable by-products previously referred to. The quantity of 

 both ammonia and healing gas may be further increased by the 

 simple expedient of passing a streamlet of steam through the 

 heateol retorts towards the end of each operation, whereby the 

 ammonia and hydri carbons still occluded in the heated coke will 

 be evolved, and the volume of heatirg gas produced le augmented 

 by ihe products of decomposition ot the steam itself. It has 

 been shown that gas 11 ay be u-ed advantageously for dome: tic 

 ] urposes with judicious management even under present con- 

 dition--, and it is easy to conceive that its comumpiion for heating 

 would soon ii crea-e, perhaps tenfold, if supplied separately at 

 say is. a thousand cubic feet. At this price gas w ould be not 

 only the cleane>t and mo t convenient, but also the cheapest form 

 of fuel, and the enormous increase of consumption, the superior 

 quality of the illuminating gas obtained by selection, and the 

 proportionate increase of by-pr ducts, would amply compensate 

 the gas company or corporation for the comparatively low price 

 of the heating gas. 



