153 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[May, 



experiments were still v. eating. According to all known analogies, they 

 ■were certainly water and nitrogen. Many works had stated that nitric acid 

 ■was also produced ; hut he could find no actual grounds for this ; and he 

 believed, like many other such statements, it had been copied from work to 

 ■work, and repeated until it had become received as a well-established fact, 

 without the slightest claim to such a consideration. In all his experiments, he 

 had never been able to finil the smallest trace of nitric acid. Ammoniacal 

 gas was very soluble in water, more so still in acids. The great avidity 

 with which it was thus absorbed, rendered its separation from coal gas very 

 easy. 



Sulphureous acid was the product of the combustion of sulphur in the 

 coal; and hydrochloric acid from the decomposition of some chlorides, 

 when they were present in the coal. Jr/iieons vapour was the result of 

 moisture in the coal. The niiror/en in coal gas was the residue of the at- 

 mospheric air contained in the retort — the oxygen of which was expended 

 in converting a portion of the carbon and sulphur of the coal into carbonic 

 oxide, carbonic acid, and sulphureous acid. Nitrogen was a colourless, 

 transparent, and incombustible gas, which, being soluble neither in acids nor 

 ■water, could not be separated from the coal gas. Carbonic acid had been 

 considered with carbonic oxide, and that completed the whole of the con- 

 stituents of coal gas. 



The illiimmatin(j principles of coal gas were olefiant gas and the vapours 

 of volatile hydro-carbons : there were also three other gases burning in the 

 coal-gas flame — namely, hydrogen gas, carburetted hydrogen or marsh gas, 

 and carbonic oxide. Besides these, the gas which we actually burn might 

 contain traces of sulphuret of carbon and nitrogen — all the rest having 

 been, or ought to have been, perfectly separated in the dirt'erent processes 

 of purification which the gas had to undergo. During the progress of the 

 foregoing short description, the audience had already become acquainted 

 with the manner in which these constituents singly burnt, but they would 

 best obtain a correct idea of the contribution afforded by each, and the illu- 

 minating power of coal gas, if they were all lighted at once. — [Dr. Hofmann 

 then lighted the burners attached to the vessels containing the separate 

 constituents, so as to afford a view, at the same moment, of all the various 

 flames.] 



By the process of purification which coal gas underwent before it was fit 

 for use, the cyanogen compounds, the sulphuretted hydrogen, the ammonia, 

 the sulphureous acid, and the hydro-chloric and carbonic acids, were sepa- 

 rated ; and he proceeded to illustrate this process by passing coal gas, con- 

 taining several of the above gases, through Itme water mixed with a little 

 potash ; after which the liquid, which before was tolerably clear, became 

 quite turgid, and the gas no longer contained the deleterious constituents. 



The lecturer then proceeded to devote a few moments to describing the 

 manner in which the distillation was effected on a large scale. In the 

 infancy of the manufacture, the coals were distilled in iron pots, but now 

 iron vessels of a cylindrical form were used. These were placed horizontally 

 in a furnace — one fire heating five of these retorts. The shape of the cy- 

 linders was not unimportant; and, after various changes, ear-shaped cylin- 

 ders were now generally preferred — its heating surface being greater than 

 that of any other. The front of the retort, or mouth-piece, as it was tech- 

 nically called, was fixed by screws — iron cement being placed between the 

 flanges to render it air-tight. — [These arrangements, as well as that by 

 ■which the lid was fixed, were illustrated by drawings and a model.] The 

 lid being fixed, the gas passed through a system of pipes into what was 

 called the hydraulic main — a long, wide, horizontal pipe, half filled with 

 ■water. Each retort was thus perfectly isolated, and the end of the pipe 

 being kept immersed in the water in the hydraulic main, any one of them 

 might be opened, in order to charge it afresh, without fear of the gas al- 

 ready generated rushing back through the opening. The temperature of the 

 hydraulic main being comparatively low, a large quantity of tar and ammo- 

 niacal water was collected in this tube, which flowed into cisterns erected 

 for the purpose. From the hydraulic main the gas passed into a system of 

 refrigerating pipes — the temperature of which was kept low by a constant 

 current of water, whereby another quantity of tar and ammoniac was sepa- 

 rated. The gas entered next into the purifiers, respecting which he could 

 not now enter into the various ingenious contrivances proposed by various 

 clever gas engineers and chemists. It would, perhaps, suffice, if he stated 

 merely, that now the gas was forced through hydrate of lime, merely 

 moistened with water. 



In conclusion, he begged to offer some general remarks upon the combus- 

 tion of coal gas. In enumerating the constituents of coal gas, he had 

 pointed out those compounds which must be considered as impurities, and 

 which must be separated before combustion took place ; but, at the same 

 time, there were others, contributing little or nothing to the illuminating 

 power of the gas, which, when once formed, could not be separated from 

 the gas. These were hydrogen, marsh gas, and carbonic oxide. Were 

 these, then, to be considered also as impurities ? If the gas were used for 

 illuminating purposes, to a certain extent at least, they must be considered 

 as impurities, because they were burnt, and in their combustion, a large 

 amount of beat was evolved ; the products of their combustion impaired 

 the salubrity of the atmosphere in which such a light was burning, and no 

 actual benefit or increase to the illuminating power was derived from them. 

 If, then, there were no means of separating these substances when once 

 formed, an effort should be made to prevent their formation. With regard 

 to carbonic oxide, it would be difficult to find a method which secured us 

 against its formation — the entrance of the retort, when being charged, being 



in commnuieation with the atmosphere. It was, however, in the power of 

 the gas manufacturer to diminish the amount of caiburetted hydrogtn, and 

 especially of hydrogen. If the temperature of the retort were too high, a 

 large quantify of the olefiant gas contained in the coal would be converted 

 into marsh gas, or even into hydrogen. That this was often actually the 

 case, appeared in a most striking manner, from the following analysis, made 

 long ago, by Dr. Henry, of coal gas made from M'igan coal : — 



Analysis of Gas from Wigan Cannel Coal 

 Time of Specific C H, or ole- C H'.', or C O. H. N. 



Collection. pravity. fiant gas. marsh gas. 



In the nrst hour .. L.„^,„ _ ,^, __ ;., ,,, __ g.g ^.3 



lU-KUt .. 12 .. .IS .. 12-:i .. IB 1-7 



5 -I Hours after the / il-,-ilio .. 7 .. .'iii .. U .. 21-3 4^7 



10/ commencement. . Ul^.-U.-) .. .. 21) .. 10 .. fiO 10 



It would be seen by this table, that it was of the greatest importance that 

 the heat in the manufacture of gas should not be carried to too great an 

 extent. In the first hour, 12 parts of olefiant gas, and 72 of marsh gas, 

 were evolved— while only eight of hydrogen were generated. At the end of 

 10 hours, not a vestige of olefiant gas was traceable ; while the hydrogen 

 amounted to 60 — evidently the consequence of the olefiant gas being de- 

 composed by the excess of heat. It had been found that, if pure olefiant 

 gas were passed through a particular temperature it became changed into 

 light carburetted hydrogen and carbon. The ratio- of this decomposition 

 was as follows : — 



C2 H2 =C H2 + C, C H2 = H2 -f C 

 So that it would be seen, that by a judicious arrangement of the heat of the 

 retorts, the production of hydrogen and light carburetted hydrogen, which 

 increased the bulk without increasing the illuminating power, might be kept 

 within certain limits. A very small quantity of these substances might be 

 present in coal gas without injurious eflfects, as they then served for the sus- 

 pension of the vapours of the oily hydro-carbons. A mixture, indeed, of 

 these vapours with carburetted hydrogen, in due proportions, might be con- 

 sidered as an equivalent to olefiant gas. Benzol, for instance, contained 

 92 per cent, of carbon ; while olefiant gas itself contained only 85 per cent., 

 and carburetted hydrogen only 7S per cent. ; and, therefore, by an admixture 

 of the latter with benzol, the illuminating power of olefiant gas might be 

 obtained. Here, again, he would mention the beautiful process proposed by 

 Mr. Low, for increasing the illuminating power of coal gas, as based upoti 

 the most scientific principles. If he wanted to express its nature in a sen- 

 tence, he should say it was a process for converting a mixture of hydrogen 

 and light carburetted hydrogen, by passing it through naptha, into olefiant 

 gas. 



This naturally led to the question — Why did hydrogen possess no illumi- 

 nating power at all ? and why was the illuminating power of marsh gas so 

 far short of the beautiful light produced by a jet of olefiant gas ? — and, 

 briefly, in what consisted the illuminating power of olefiant gas ? The il- 

 luminating power of gas depended upon a portion of it being separated in 

 the solid form, which, being deposited at a certain distance between the 

 orifice of the burner and the rim of the flame, entered into a state of igni- 

 tion, from which the light emanated. Now, the composition of coal gas 

 was such, that if it were allowed to issue from a convenient burner, a com- 

 plete combustion of the hydrogen was obtained, but only a partial one of 

 the carbon. Another portion was separated — that which entered into a 

 state of ignition being heated to a white heat before it reached at sufficient 

 temperature for its combustion. 



In the flame of coal gas, three different parts, or cones, might be distin- 

 guished. Immediately over the burner, it was principally hydrogen which 

 was burnt, along with a little carbon, whilst the main portion of the carbon 

 being thus set free, was ignited in the second cone, and consumed with the 

 rest of the hydrogen in the outer flame. By a simple arrangement, the illu- 

 minating power of the coal gas might be destroyed altogether — namely, by 

 mixing it, previous to combustion, with a sufficient amount of air to produce 

 a complete combustion. The illuminating power of coal gas — and, in fact, 

 of any flame — depended entirely upon the deposition of a fixed body in the 

 flame. It was by no means necessary that this body shoidd be carbon. It 

 might be anything else — such as lime, iron, &c. — [The talented lecturer 

 then rendered the flame of hydrogen luminous, by passing through it a 

 chloro-chromic acid ; and this interesting lecture was concluded by several 

 clever experiments, illustrative of the various subjects it embraced.] — 

 Mining Journal. 



STEAM ■W^ORKING EXPANSIVELY. 



On the Iiifumrc if Tiiipid Mntinn of the Pi>:ton upon the Effect of 

 Stennt in Engines jrorkiug E.rpinisive/y : with Ejcperimentu upon the 

 .luhjert. By M. 1'althinebi. — (Translated for tlie Jonruul of the 

 Franklin Institute.) 



The researches ami iiunierotis experiments whicli I have made 

 upon the application of motive power to machines, and particularly 

 my e.tperiments upon the effect of springs, have convinced me that 

 in the expansion of steam there is a loss of power : a loss which 

 should have a certain relation to the number of superimposed strata 

 of steam which occupy the cylinder, from its bottom to tlie piston. 



