40 1 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



TDecembkr. 



power of all gaseous flniils to ascend is " inversely as the square roots of their 

 specific gravities," the velocity of its escape hy the chimney, compared with 

 common air of the same temperature, is about as 1'4 to 1; therefore the 

 compnund mixture of steam, air, and carbonic acid gas, will escape with a 

 considerably increased velocity, and more air must consequently enter the 

 furnace. It appears that about 10 per cent, of the total quantity of steam 

 generated is necessary to effect the combustion of the smoke by this means; 

 therefore, unless the waste steam only be used, the saving of the fuel must 

 be reduced by this amount. Brief mention is made of the experiments of 

 Messrs. Apsley Pellatt, Parkes, and the Chevalier de Pambour, proving that 

 a given quantity of oven coke will produce as much heat as the coal from 

 •which it was produced ; and of the various kinds of artificial fuels which had 

 been invented, especially that composed of resin and peat coke, of which the 

 author remarks that its combustion probably produces a mechanical effect, 

 as the hydrogen is converted into water in a state of vapour, which escapes 

 through" the chimney with a great velocity, and consequently a large quan- 

 tity of air is drawn into the furnace, and a more perfect combustion of the 

 fuel is the result. In the same manner he accounts for the necessity which 

 exists for having the openings between the bars wider in a furnace in which 

 coke is burned than in one used for coal. In opposition to the general 

 opinion, he considers that less air is required for the consumption of coke 

 than for coal ; the carbon only requiring 21 times its weight of oxygen for 

 its combustion, while the hydrogen contained in coal requires 8 times its 

 weight of oxygen ; and the only reason that the openings between the bars 

 are required to he wider in the former tlian in the latter case, is in conse- 

 quence of the draught being so much slower during the combustion of coke 



.■Jdly. " On the nature and application of the volatile products of coal." In 

 treating this portion of the subject — many of the observations on which have 

 l)een necessarily anticipated in the preceding sections — the author traces the 

 ajiplication of carburetted hydrogen gas to the purposes of artificial illumi- 

 nation from the year 1798, when its first successful application was made by 

 Murdock at Soho ; lie then proceeds to Dr. Henry's investigations of the 

 phenomena of its production and combustion ; the variation of the intensity 

 of light obtained from carburetted hydrogen, due to the proportion of carbon 

 contained in it; the difference in the gas olttained from different qualities of 

 coal ; the superiority of the illuminating power of the gas from Cannel coal ; 

 and the still greater power of that produced from the decomposition of oi], 

 which is 2 to 2i times greater than that of coal gas. He then mentions the 

 other products of coal by distillation, such as ammoniacal liquor, carbonic 

 acid and oxide, sulphuretted hydrogen, tar, essential oil, naphtha, petroleum, 

 asphaltum, and other substances. The paper concludes by jjointing out the 

 advantages which would result from the jiioduction of such gas as is usually 

 given out at the beginning of the distillation of coal, as it contains 2 volumes 

 of gaseous carbon united with 2 volumes of hydrogen, and its illuminating 

 power is consequently more than double that of ordinary coal gas. 



Mr. Parkes observed, that the quantities of air required for the combustion 

 of different fuels as determined in the laboratory and on the large scale of 

 practice, were frequently very different. It might be quite correct that a 

 given weight of coal would require more air for its perfect combustion than 

 the same weight of coke. There was great difficulty in ascertaining the fact 

 practically, under steam-boilers, as the gases given out by the coal must have 

 air supplied to them distinct from that which passed tlirougb the grate to 

 ensure their perfect ignition, and many circumstances prevented the con- 

 sumption of air from being exactly measured. Generally, be bad found it 

 necessary to use wider spaces between the grate bars for coke than for coal. 

 In some'late experiments very carefully made on a boiler invented by Mr. 

 A. M. Perkins, equal weights of coal and coke required the same time for 

 their destruction on the same grate, the apertvu'es of the damper and ash-pit 

 door, which were used to govern the draught being precisely the same. Coke 

 effected a greater evaporation than coal at similarly rapid and slow rates of 

 combustion ; and in every case the temperature of an oil bath at the foot of 

 the chimnev was higher with coke than with coal. It must, however, be 

 remarked, tliat no process had been used to ignite the gases which escaped 

 from the furnace uniuflamed. He had tried different kinds of coke, coal, and 

 anthracite at this boiler, and the same fuel in every instance performed a 

 greater evaporative effect at a slow than at a rapid rate of combustion. He 

 thought that much of the air which entered the grate of a boiler passed 

 through the fire unconsumed, for want of time to effect a sufliciently intiuiate 

 combination with the fuel. In some experiments lately made at Swansea on 

 the properties of anthracite. Dr. Schaftcutl had found from analysis, that no 

 less than 40 per cent, of the products of combustion taken from the chimney 

 consisted of oxygen, yet he had effected the large evaporation of 11 lb. of 

 water with 1 lb. of that fuel. 



Mr. Field stated, that Mr. Cooper had expressed an opinion that in the 

 use of coke as a fuel, a less portion of heat reached the chimney than with 

 coal, on account of the large quantity of unconsumed air that ])assed through 

 the fire, owing to the open spaces necessarily existing between the pieces of 

 such a dry fuel as coke ; whereas in a fire made of binding coal, nearly the 

 whole of the air combined with tlie fuel in its passage through the body of 

 fire. 



Mr. Pellatt observed, that although in practice coke appeared to reqmrc 

 more air to support combustion than coal did, yet long experience had taught 

 him to believe that when coal was exposed to a rapid combustion, it required 

 more air than coke. 



In answer to an observation that some experiments lately made on the 



measurement of the quantity of air which entered the blast furnaces of Sir 

 John Guest at the Dowlais Iron Works might bear on this subject — Mr. 

 Farey objected to the application of such results to determine the question, 

 as the air is injected with considerable force into a furnace; there is fie- 

 quently a great reflux of blast from the Tuyere when the furnace is workiiig 

 close; whereas when it is working open tlie flame at the top shows that the 

 l>assage of the air through the mass of burning fuel is very free, and that 

 consequently a portion of it passes off unconsumed. He had found in his 

 experiments on blast furnaces, that unless there was a redundancy of carbon, 

 and a deficiency of oxygen, there was no chance of making good iron. 



May 26t/t. — The President in the Chair. 



The following were balloted for and elected : — Thomas Illman, Joseph 

 Chessborough Dyer, and G. S. Saunderson, as Associates. 



'■ On a new Mode of Coreriny Roofs with Planking." By William Cubitt, 

 Assoc. Inst. C. E. 



The roof itself is framed in the usu.il manner with principals and purlins, 

 but without rafters. The boards intended for the covering are cut, by means 

 of a circular saw, from planks 7 inches wide by 2i inches thick, in such 

 manner that each plank makes Xv;o boards, the one tapering from its centre 

 towards the edges, the other from its edges towards the coitre. The hollow 

 boards are laid side by side, at intervals of 41- iuches, and nailed to the pur- 

 lins by their centres only, so as to admit of shrinking ; the intervening spaces 

 are then covered by the other boards, overlapping \^ inch on each edge, and 

 nailed in like manner. The covering thus formed presents a series of alter- 

 nate elevations and depressions, longitudinally from the ridge to the gutter, 

 and consequently the rain falls off very rapidly, and a roof so constructed is 

 easily kept water-tight. The author conceives this to be the most economical 

 mode of using timber for covering, and he has adopted it extensively. The 

 communication was accompanied by a model of the roof and specimens of 

 the hoards as they are left by the saw. 



'* On Lony and Short Connecting-rods for Marine Eityines." 



A letter was read from Ardaseer Cursetjee, of Bombay, in^^ting a discussion 

 on the relative advantages of long and short connecting rods for marine 

 engines. He was induced to make inquiry on this subject from some obser- 

 vations in a communication to the Institution, relative to the engines of the 

 steam tug the " Alice " (Minutes of Proceedings, page 385). In that paper 

 their superiority is in part attributed to the increased length of the coimecting 

 rods. This is the point upon which he requests information, as he conceives 

 that the power of the piston upon the crank is the same whatever may be 

 the medium through which it is transmitted, and the effect to be the same 

 throughout a complete revolution, whetlier the connecting rod be long or 

 short, except that from the increased angle of a very short connecting rod 

 some additional friction is thrown upon the joints. 



On the general construction of the engine of the " Alice," he remarks, that 

 engines of similar form are now used for pumping at the Tliames Tunnel 

 under Mr. Brunei's direction ; and that a pair of engines of this kind were 

 built by Messrs. Seaward, 13 years ago, for the " Staadt Francfort " steam- 

 boat, to ply between Francfort and Coblentz ; in this instance, the cylinders 

 were firmly fixed to the bed-plate and sleepers, with the cross bars above the 

 cylinders, thus having one connecting rod only leading to the cranks, which 

 he considers a superior arrangement to that of the engines of the " Alice." 



A drawing of the engines of the " Staadt Francfort " accompanies the 

 communication. 



A letter was read from Mr. John Cooper, of Dover, describing the effect of 

 the worm (Teredo navalis) on several kinds of timber which had been ex- 

 posed to the action of sea water. The kinds of timber on which the experi- 

 ments were made were fir, English oak, and African oak ; specimens of each 

 sort, some Kyauized and the others unprepared, having been tried under ex- 

 actly similar circumstances on the piles of the south ]iier of Dover harbour. 

 The results show that Kyanizing timber does not in any degree protect it ; 

 as, after exposure from December 1837 until May 1840, it was fouml that 

 the worm made equal ravages among all the specimens. The author also 

 tried the process of saturating timber with copperas water, but did not find 

 any good result from it. In July 1835, he placed under water some 2-incli 

 oak planks which had been prepared with copperas ; and on examining theiu 

 in May 1840, they were found to lie as much attacked by the worm as the 

 worst specimens of unprepared fir timber which had been exposed for a similar 

 length of time. The African oak resisted the attack of the worm better than 

 either fir or English oak. 



It was stated that Teak timber resisted the attacks of the worm and of the 

 white ant, which destroy all other kinds of timber. It is, however, liable to 

 injury from the attacks of liarnaoles. 



•' On the Corrosion of Cast and Jl'ronght Iron in Water." By Kobert 

 Mallet, Assoc. Inst. C. E'., &c. 



This communication is one of those forwarded to the Institution in conse- 

 quence of the Council having considered this subject a suitable one to com- 

 pete for the Telford Premiums ; and the author having been long engaged in 

 making experiments on this subject at the request of the British Association, 

 refers in the introductory part of this paper to the contents of that report, 

 which may be viewed as a '■ precis" of the state of our knowledge on the 

 subject to tlie year 1S39, together with original researches forming the basis 

 of the present results. This communication is accompanied by a most elabo- 



