1S3G.] 



FARMERS' REGISTER, 



481 



which u copious table was shown, containincr also 

 a starement of the relative proportions ol' gas, 

 condonsihie products, and coke, ailbrded by three 

 varities ol" coal. Models and drawinirs of gas ap- 

 paratus were then described, especially as illustra- 

 ting the diU'ercnt modes ol" setting the retorts; 

 and the progress of the gas from them was traced 

 througli the hydraulic main, where the far, water, 

 and ammoniacal liquor, are chiefly deposited to 

 the condensers, purifiers, and gasometeis. Some 

 observations were then niade in reltMcnce to the 

 uses and properties ol" the various products, in the 

 Ibllowing order : — 



1. Ammoniacal Liqiinr. This was shown to be 

 a complicated solution of several ammoniacal and 

 cyanic compounds in water. It is extensively 

 used for fhe production of muriate of ammonia, 

 wli^jeh is obtained by saturating it with muriatic 

 acid, evaporating, cr\'sta!izing, carefully drying 

 the crj-stalized salt, and subliming it into large 

 leaden receivers. A beautiful specimen of this 

 salt, prepared by Mr. Leeson, of Greenwich, and 

 weighing 2 cwt., was exhibited. Sulphate ol"am- 

 monia is also prepared from the liquor; this, in its 

 dry, crystalline state, is mixed with carbonate of 

 lime, and alfords carbonate of ammonia, of which 

 a large mass, prepared by J\3r. Leeson, was also 

 shown. The presence of sulphocyanic and hy- 

 drocyanic acid in the ammoniacal liquor was 

 shown by saturating it with muriatic acid, and ad- 

 ding i)ersidphate of iron ; the detection of these 

 conjpounds and their application to the manuitic- 

 ture of Prussian blue, Mr. Urande said was ow- 

 ing to the s'kIII and ingenuity of i!vlr. Lowe. This 

 product, therefore, of the gas manufacture, once 

 considered as useless, yields a variety of useful 

 and important compounds, and has opened a new 

 field of chemical art. 



2. Tar. This [)roduct is useful as a coarse paint, 

 and lor the purpose of paying and caulking ves- 

 sels : it is also more importantly ap|)Iicable as fuel 

 in the gas-works, where, ndxed with water, it is 

 sufl'ered to dribble into the Ore: three gahons of 

 this mixture per hour being sufficient to heat five 

 retorts. When distilled, it yields naphtha, a high- 

 ly volatile and inflammable liquid, which is occa- 

 sionally burned in lamps, or used as a solvent in 

 the manufacture of certain varnishes. 



3. Lime Liquor. This is the mixture of lime 

 and water, through which the gas has been pass- 

 ed, chiefly with a view of" freeing it from carbonic 

 acid and sulphuretted hydrogen : it is fr-om time to 

 time drawn f"rom the purifiers and sufl'ered to 

 subside. Tke deposite, or thick portion, is made 

 again into lime, or is used lor luting the retort-lids; 

 the clear portion is pumped into shallow vessels 

 placed i:i the ash- pats of"the retort-furnaces, where 

 it evaporates, and tends to preserve the bars, pro- 

 bably by keeping them cool. Another use, how- 

 ever, is now made of it, as follows : Acid persul- 

 phate of iron (copperas liquor) is added to it, 

 which throws down a green precipitate, that may 

 itself be used as u paint, but which, digested in a 

 solut-ion of potash, yields a ferrocyanale of potash, 

 sufficiently pure to ihrow down Prussian blue f"rom 

 common copperas liquor. 



4. Gas. This specific gravity of the purified 

 gas, and, consequently, its composition, vary 

 considerably at diiterent periods of the distillation ; 

 its average specific gravity, as taken f"rom the gas- 

 ometers, is 0.410 ; each cubic foot weighing 240 



Vol. IV— 61 



grains. Alter some remarks upon the manufac- 

 ture of gas generally, and upon (he various Ibrms 

 of carbon, and other products occasionally found 

 in the retorts. Mr. IJrande made some observa- 

 tions upon the sources of" the luminosity of differ- 

 ent gases, and on photometers ; ami then proceed- 

 ed to details connected with the process as carried 

 on upon the large scale by the difi'ercnt companies; 

 stating that his experience was chiefly derived 

 from the Chartered (xas Company, the officers of 

 which had most assiduously assisted him in all in- 

 quiries connected with the subject generally, and 

 with the particular object of the present incjuiry ; 

 Mr. Lowe, and Mr. Frederick Wiiisor, had kind- 

 ly given him access to their information ; and Mr. 

 Crossley had supplied models of gas-meters and 

 their appendages, with much of the other appa- 

 ratus upon the table. Mr. Brande estimated the 

 number of retorts worked by the above-men- 

 tioned company at 750; and assuming them to 

 be about one-fourth of" the number employed in 

 London, the whole amount will be 3,000 re- 

 torts, of about 15 cwt. each ; so that the cast iron 

 thus employed, to say nothing of the enormous 

 amount in pipes and other apparatus, amounts to 

 2,240 tons. The total stowage lor gas in the gas- 

 ometers of the Chartered Company, Mr. Brande 

 estimated at 820,000 cubic feet; or. for London, 

 3,280,000 cubic lijet. He said, that the number of 

 burners supplied by this company amounted to 

 about 42,000 ; or, lor the whole of London, to 

 168,000; and, estimating the consumption of each 

 burner at five cubic feet per hour, (he averag'i 

 hourly consumption of gas would amount to 

 840,000 cubic feet ; and taking five hours per day 

 as the average time of burning, we have 4,200,- 

 000 cubic feet of gas as the daily average con- 

 sumption. Mr. Brande concluded by explaining 

 the different checks resorted to by the companies 

 in reference to the quantity of gas produced and 

 consumed; and by a description of" (he gas-me- 

 ters, pressure-gauges, tell-tales, and governors, 

 all illustrated by a series of excellent models and 

 apparatus. The following tables were exhibited, 

 as furnishing data and details connected with se- 

 veral of the points referred to in this lecture, to- 

 gether Avith some others which we have not room 

 ibr, showing the relative weights and volumes of 

 gas, and of the consumption of atmospheric air in 

 its combustion : — 



For the total annual supply of gas to the me- 

 tropolis, there are required 200,000 chaldrons of 

 coal, yielding 2,400.000,000 cubic feet of gas ; the 

 gas weighing 75,000,000 lbs. The light thus 

 produced is equal to 100,000,000 lbs. of mould 

 candles, of six to the pound ; the bulk of the coal 

 is equal to 10,800,000 cubic feet, or 400,000 cubic 

 yards ; or to a cube of 222 leet in the side, or of 

 74 yards. 



From llie London Farmer's Magazine. 

 OF MONEY AS A MEDIUBI OF EXCHANGE. 



By Charles Babbage, Esq. Lucasian Professor of Ma- 

 thematics ill the University of Cambridge. 



In the earlier stages of societies, the interchange 

 of the l"evv commodities required was conducted 

 by barter; but as soon as their wants became 

 more varied and extensive, the necessity of having 



