SD3 



THE CIVIL EXGIXEER AND ARCHITECT'S JOURNAL. 



I^Decembbr, 



The experiments of I\Ir. Nicholas Wood, Mr. G. Elliot, Mr. H. Vidian, 

 and other mining eoijiiiecrii, were then quoted, to demonstrate the insutK- 

 ciency of the " steam jt^t," as a means of proiiioliu^ venlilaliou, sliowing 

 that it was a most wasteful application of power, when compared with 

 the steam force employed to work Struv^'s Mine Ventilator at the Eagles- 

 bush Colliery. This apparatus consisted of two hollow pistons, resem- 

 bling large sasometers plunging into cisterns of water, and having inlet 

 and outlet valves. The pistons received alternate motion from a small 

 steam-engine of .5-hiirse power; and being fdled and emptied at each 

 revolution of the crank, produced a regularity of current and a degree of 

 copious ventilation liilherlo unknown in the mines to which ihey had been 

 applied. The small cost of their establishment — only about one hundred 

 pounds for au extensive mine — ^joined with the little liabilily to getting 

 oat of order, was much in their lavour. 



The paper tfrminali'd with copious extracts from the able mining 

 reports of Mr. John Pliillips and Mr. Kenyou Blackvvell, confirming all 

 the positions assumed by the author. 



Nov. 20. — The discussion upon Mr. Struve's paper occupied the whole 

 of this evening, and will be resumed on Tuesday, December 3rd. 



We understand that a Telford medal in silver has been awarded to 

 G. B. Thorneycroft, Esq., of Wolverhampton, by t!ie council of the Insti- 

 tution of Civil Engineers, for his paper "On the manufacture of malle- 

 able iron, and on the strength of railway axles," read during the session 

 of lS-19-aO. The medal will be presented at the annual meeting on Tues- 

 da> evening, the ITIh of December next. 



ROYAL SCOTTISH SOCIETY OF ARTS. 



Tins Society cuiiiiiK-nced its annual sittings on the 1 1th ult., in its new 

 and commodious hall, Ceorge Street, when Thomas Grainger, Esq., C.E., 

 the Vresideni, opfiied the session by an eloquent address. 



The following I'aper was read : — 



".In Account n/the Chimnaj nf the Edinburgh Gns-Woiks, with Obser- 

 vations ok the Princiides nj'its Strength and Stahilili/. By Guoroe Bu- 

 chanan, Esq., F.R.S.E., C.E. 



In Part I. of this paper Mr. Buchanan gave a very interesting account 

 of this remarkable structure, and the principles of its strength and sta- 

 bility. It was one of the works particularly alluded to by the President 

 ia his interesting introductory addre.ss last year, and of which he tliought 

 it important that the Society should have some account; and Mr. B. 

 having been professionally connected with the work, had much pleasure, 

 at the President's request, in now stating what he knew of it. Having 

 communicated also on tlie subject with the Gas Company, Mr. Al'atson, 

 the manager, was most anxious to give informatioa and every facility iu 

 his power to forward the great objects of the society; and Mr. Taylor, 

 the engineer of the works, and by whom the chimney itself was designed, 

 has made out a detailed description and drawing, showing minutely the 

 dimensions and structure of every part of the work, and which he now 

 requests Mr. H., along with his paper, to present to the society. 



It was about the year 1S4S, owing to the extension of the works, that 

 it became necessary to obtain increased chimney accommodation, both for 

 increasing the draught of the furnaces and for carrying ofi' the smoke and 

 vapours from the works, and clear away from the neighbourhood by raising 

 the chimney to a greater height. Three chimneys were then on the works, 

 the highest of them risiiig 14S feet, and not exceeding 2J feet square 

 internally at the top. 'J'hese gave vent to the smoke and vapours of OS 

 furnaces, heating 17S retorts, but were inadequate to work these effec- 

 tually, and to give proper ventilation for cooling and purifying the retort 

 houses for the comfort of the workmen, still less to meet the extensions of 

 the works then contemplated and since executed. Instead of continuing, 

 however, the system of small and low chimneys, and adding to their 

 number, the plan came lo be considered of raising one siugle chimney, 

 suHicienlly large and lofty to receive the flues from all the furnaces, and 

 by one powerful column of hoated air to work these, and any contemplated 

 extensions, in a more eliectual manner than hitherto, and so as to super- 

 sede the others and render any addition unnecessary for a long period. 

 The idea had been acted on in some works already, and the maguilicent 

 chimney of St. Rollox chemical works furnished a favourable example. 

 No way deterred, therefore, by the anticipated difficulties, or the great 

 cost of the underiaking,* seeing especinlly that it promised beneficial 

 results to the public, the directors determined to proceed with the plans 

 made out at their request by Mr. Taylor. Having previously, however, 

 requested Mr. Buchanan's opinion and advice thereon, he then carefully 

 considered the whole subject, approved of the general design, and sug- 

 gested only slight modifications in the form of the column and other points ; 

 but to Mr. Taylor still belonged the merit of the design, which he thought 

 was great, as well as his talents and skill ia superinleudiug the work. 



Mr. B. then proceeded to state from his reports some of the facts and 

 principles regarding the work, which apply generally lo all similar under- 



* The wliole cost of the work has been little short of 5000?. One of much less magni- 

 tude would have been sufficient for immiMliiite wants— but after due consideration they 

 thought it best to do the plan effccluall.r at once. 



takings. And, first, in regard to the form of the structure, whether round 

 or square ; the square had been usually adopted in the works, but iu the 

 case of an altitude from 3U0to 400 feet the round form was decidedly to 

 be preferred, as presenting a less elTective surface to the wind, whose 

 violent action in this quarter it was important to diminish by every means. 

 The efl'ect of the wind on a cylindrical surface as compared with a square 

 had been calculated by theory in the ratio of two to three. This is the 

 Law of Resistance so beautifully demonstrated by the commentators on 

 Newton's Principia. Subsequent experiments had proved the effect ou 

 the globe and cylinder to be, if anything, ral her less than theory, so that 

 we are quite safe in taking it at 3 ; the result is, that with 300 tons, for 

 example, acting on a square tower, we have only 20i) on the cylinder of 

 the same diameter, which is most material. The bricks also, by being 

 moulded lo the circle, can be built and bound together with all the strength 

 of the arch. On (he lower part of the building, again, which is less ex- 

 posed, and to be built of stone, the square and pedestal form are preferable. 



Secondly. The building being intended to be 300 feet and upwards iu 

 height, the question arose how far the ordinary brick could withstand the 

 pressure arising from so lofty a column. This diliiculty was provided for 

 by the increasing thickness of the walls of the chimney from the top 

 towards the bnltom, whereby the incumbent pressure being distributed 

 over a larger and larger surface in descending, was diminished in propor- 

 tion. The whole height from the foundation 10 the top is 341i feet; of 

 this 77.'. feet are occupied by the foundation and square pedestal of stone, 

 and 204 feet by the brick-work, the tiiickncss of which was diminished 

 towards the top by five successive steps. The upper division extended 83 

 fe'jt down, and was 1.5 inches thick, and the internal diameter 11 ft. 4 in. 

 at top ; the 2nd division .'iS feet and 2t> inches thick ; the 3rd, 48 feet and 

 2.5 inches ; the lib, 40 feel and :;0 inches; and the ijtli, 35 feet and 35 

 inches thick, and internal diameter 20 feet. On calculating the weight 

 and pressure on each of those divisions, on the first it was found not to 

 exceed 4! Ions on each square foot; in the middle it increased to 7 tons, 

 and at the base it increased to 8 tons on each square foot. The strength 

 of ordinary brick being estimated at from 20 lo 30 tons, the work seemed 

 within the limits <.f safety ; but on finding that a cumpusitioa brick could 

 be obtained in the neighbourhood, from the brick works of Mr. Livingston, 

 of .Joppa, 01 ranch superior strength, Mr. Buchanan strongly recommended 

 these, and also suggested experiments on their strength, of which he 

 would give farther details ou anotiier evening, but found the first specimen 

 tried bore at the rale of 440 tons to the square foot, a degree of strength 

 almost incredible in such material. The results of the other experiments 

 were somewhat similar, and all sncli as to set at rest any fears of the 

 result. In regard to the suliiciency of the foundation itself, although this 

 sustained the whole mass of the building, amounting to 4000 tons, yet the 

 weight being spread over the entire area of the solid base, 40 feet square, 

 it did not exceed 2A tons to the square foot. And the material consisting 

 of very hard till or blaes, of pretty equal solidity throughout, this ap- 

 peared to form a good and sufficient foundation; and in order to be per- 

 fectly secure, the building at one of the angles was carried deeper than 

 the rest, to obtain the same hard and solid bearing throughout. The result 

 of these precautions, it is now very satisfactory to observe the structure 

 standing perfectly upright and entire, without a crack or Haw of any 

 description to be found iu il. 



The next object of importance that came to be considered was the efl'ect 

 of high winds on the building. I'roni experiments, it was calculated that 

 the force of a storm or tempest is equal to 12 lb. ou the square foot of sur- 

 face directly exposed ; a great storm 181b., a hurricane SO lb., and one 

 capable of tearing up trees and oversetting buildings, ."lOib. There is no 

 instance, however, of such a hurricane occurring in this country, and we 

 are quite safe in assuming 401b, per foot, or 90 miles an hour, as the 

 utmost power of the wind in this country. The French engineer, Fresnel, 

 in an iulerostiug memoir on the stability of the lighthouse of I'lelleisle and 

 various other lighthouse structures compared with it, has assumed the 

 force of the wind at .55 lb., agreeing with the estimate of another engineer, 

 Navier; but this is evidently much beyond the truth, and the effect was 

 to bring the gas-chimney in Paris below the zero of stability, although it 

 stands as yet quite secure. Consider only the human body, which presents 

 a surface from four lo six feet square. Such a force of wind would be 

 equal to a pressure of from 200 to 300 lli., and the power to overset at 

 least equal to 5001b., which no one could sustain for a moment, and even 

 the ordinary inclosure-walls or chimneys would be immediately prostrated 

 by it. Besides, it appears from observations of wind gauges, and particu- 

 larly of cue by Mr. Adie of this cily, that the greatest force indicated on it 

 for several years was only IV, lb. ; and another gauge, kept for several 

 years at (iranton Pier, and now at the Observatory, never indicated more 

 than 18^ lb., and this was at Grantou on the 9th and 27th ot April, 1847. 

 If we allow 401b., therefore, we are quite safe, this being nearly double 

 what ever occurs. 



Another point must he kept in view, that the tendency to overset the 

 structure is greatly increased by the altitude, and this in fact exactly in 

 proportion as the height exceeds the breadth of the base. It might happen 

 also, if the strength of ihe ditl'erent portions of the column were not duly 

 proportioned, that it might be overset, not at the base, but at some inter- 

 mediate point between it and the top. Applying these views, it was found 

 that in the upper division, 83 feet down from the top, the force of the wind 

 was 145 tons, and this increased by Ihe height and narrow base to 70 tons. 



