1849.J 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



119 



and length of tubes, and also the speed of the engine. It may be 

 remarked, however, that on tlie average a degree of exhaustion is 

 required in the fire-box under ordinary circumstances equal to a 

 column of water •!■ inches in height, and the degree of exhaustion 

 in the smoke-box must of course be greater tlian this l)y the re- 

 sistance offered by tlie tubes to the passage of the heated gases 

 from the fire-box to the smoke-box. 



From experiments made about 94 years ago upon an engine 

 with a total heating surface of 987 feet, carrying 1+7 tubes of l|- 

 inch external diameter and 13 ft. 10 in. long, the author found that 

 the latter force was at all velocities three times as great as the 

 former; or in other words, that 66 per cent, of tlie total foixe of 

 the blast was required to overcome the resistance offered by the 

 tubes to the passage of the heated gases, leaving 33 per cent, only 

 to operate upon the fuel; and it is this evil which results from the 

 comparatively limited flue area of the boilers as at present con- 

 structed, to which attention is now more particularly called, and 

 which it is projjosed to remedy in the manner now to be explained^ 



From what has been said it will readily be inferred that there is 

 some difficulty in materially increasing the power of locomotive 

 engines, as the necessary amount of heating surface cannot be ob- 

 tained without increasing the diameter or the length of the boiler, 

 or making it oval, to all of which plans there are some objections: 

 but by the method now proposed it will be easy to enlarge botli the 

 fire-box and tube surface from 35 to 40 per cent., without increas- 

 ing either the diameter of the boiler or its length, as will he now 

 shown. 



It is proposed to construct the copper fire-box with an arched 

 roof, the top of which shall be nearly as high as the top of the 

 cylindrical part of the boiler This box may of course be made 

 any length without sensibly reducing the strength of the roof, and 

 will require none of the stay-bars which are so essential to the 

 security of the flat-roofed box, and which for a moderate sized 

 engine weigh not less tlian 400 lb. 



With such a box the whole of the cylindrical part of the boiler 

 can be filled with tubes, and of course the whole of the longitu- 

 dinal stays be removed; and in the present instance there are 225 

 tubes of 2 inches external diameter, the shell of the boiler being 

 3 ft. 8 in. diameter and 10 feet long; the total heating sui-face of 

 the fire-box is 80 feet, and of the tubes 1,177 feet, making a total 

 heating surface of 1,257 feet. Such an arrangement involves the 

 necessity of keeping the boiler full of water, and it is therefore 

 requisite that a separate steam-chamber should be provided. This 

 consists of a cylinder which is 13 feet long and 20 inches diameter, 

 fixed over and parallel to the cylindrical part of the boiler, or, as it 

 may now be termed, the generator. This tube, which has a cubic 

 capacity of 28^ feet, is connected at each end with the generator. 

 It is proposed that tlie water shall occupy about one-fourth of tlie 

 capacity of this tube, leaving a clear space of say 21 cubic feet for 

 steam; this is rather more steam-room tlian most modern boilers 

 possess, and for reasons which are afterwards mentioned, tlie 

 author thinks it will be sufficient, although it may readily be in- 

 creased by slightly enlarging the diameter of the steam-chamber, 

 which as at present shown, is not so high as the ordinary steam 

 dome by about 12 inches. 



It has been proved experimentally by Mr. Robert Stephenson 

 that the generative power of the copper fire-box is three times as 

 great per unit of surface as that of the tubes; and independent of 

 this authority, locomotive engineers are generally agreed that 

 the great bulk of the steam generated in a locomotive boiler is 

 formed upon the surface of the copper fire-box, and the first 18 or 

 20 inches length of the tubes. As the whole of the steam has to 

 rise through the body of the water with which it is for the time 

 mechanically mixed, and as the specific gravity of these mixed 

 fluids will be much less than the comparatively ?(??mixed water at 

 the smoke-box end of the boiler, it follows that there will be a brisk 

 circulation through the generator and steam-chamber. The mixed 

 steam and water will be driven into the upper vessel, and will 

 there be effectually separated; the former passing off to the cylin- 

 ders by the longitudinal pipe, which has a number of small holes 

 upon its upper surface, and the latter running again into the 

 generator through the vertical connection at the front end, and 

 thus keeping up the circulation. 



That the specific gravity of the mixed steam and water at the 

 fire-box end is often reduced to at least one-half that of water 

 alone, is proved by the fact that the water-gauge will frequently 

 show a downward current through the glass tube, even thougli 

 the circulating fluids be one-half water and one-half steam, show- 

 ing as it does that the column of the mixed fluids in the boiler 

 is specifically lighter than the column in the glass gauge; and 

 from this fact it is also evident that this great expansion is con- 



fined to the water in the vicinity of the fire-box, since if it ex- 

 tended to the whole mass, the boiler would not contain the requisite 

 quantity. 



From the circumstance that no bubble of steam can rise into 

 the steam-chamber between the points marked A and B, it is 

 concluded that this boiler will not be so liable to prime as the 

 common one, and therefore that the steam-chamber as shown is 

 sufficiently hirge. As to the water surface, which in this boiler it 

 may be objected is smaller than in others, it is conceived tliat the 

 great facilities this boiler will give to the engineer for raising 

 steam, will leave him comparatively at liberty to put in water 

 wlien and where he chooses, and consequently that but little diffi- 

 culty need be apprehended on this point. It is evident however 

 that the objection may be fully met by constructing the outer fire- 

 box with a pyramidal roof in the way so common. 



In conclusion, the author would express his conviction that this 

 boiler, comliining as it does a great increase of heating surface, and 

 correspnnding increase (if flue area, with a relative diminution of bulk 

 and weight, and great simplicity of construction, is calculated to 

 remove some of the difficulties experienced by locomotive en- 

 gineers, and to promote the best interests of the railway world in 

 general. 



Remarks made at the Meeting after the reading of the foregoing Paper. 



1 he Chairman said, that in the unavoidable absence of Mr. Ramshottom, 

 he won d observe that his object in the toregoing paper was to obtain a con- 

 sideiahly larger arfa of flue- room than in the present locomotive boilers, and 

 to make a boiler of a large lieating-surface with less weight. 



Mr. Slate was of opinion that for the weight the engine carried, it would 

 lia\e a considerably greater effective heating-sutface than any previous form 

 of boiler ; hut he thought the boiler would have as great a tendeucy to prime 

 as any other. 



Mr. CowpEB was also of opinion there would he a great tendency to prime 

 in the proposed boiler; the surface from wliich the steam had to rise was the 

 entire surface of the fire-box and tubes, and all the steam had to pass 

 through the two openings into the steam-chamber, and it appeared to him 

 the water would be carried up there in a complete state of froth. 



Mr. McCoNNELL, while agreeing to a certain extent as to the liability of 

 the boiler to piime, thought it might he obviated by having a more continu- 

 ous communication between the generator and the steam-chaniher; perhaps 

 the steam-chamber could be fixed close upon the top of the generator, and 

 a continuous longitudinal opening be made, communicating between them 

 throughout their entire length. He thought the proposition of Mr. Rams- 

 hottom was a very good one, as it was a received opinion that the proportion 

 of the flue-room to the fire-grate surface could not be too large, supposing 

 that full advantage was taken of the flue surface before the heated air 

 reached the chimney. Whether long tubes or short tubes as applied to lo- 

 comotives were most advantageous, was a question not yet decided, and he 

 thought they had scarcely data enough to determine as to the advantage of 

 long tubes on the ground of economy. It was a very important matter to 

 licti'mrine what length of tubes was most advantageous fur use in proportion 

 to the area of the fire-grate. 



Mr. C. CowPER was not aware whether there was any authority respecting 

 the proportionate heating power of the tubes and the fire-box, besides the 

 experiment of Mr. Stephenson alluded to in the paper. 



Mr. McCoNNELL remarked, that it appeared from experiments made by 

 Mr. Stephenson and Mr. Beyer, that a very considerable heat was lost in the 

 sinnke-hox even at the end of the longest tubes that mere used; and he 

 thought that the air in the centre of the tubes might have a considerably 

 higher temperature than the air at the sides of the tubes, and that much of 

 the heat might he carried through by a stream of air like a solid bar in the 

 centre of each tube, without ever coming in contact with the sides of the 

 tube, and consequently without being communicated to the water of the 

 boiler. He had been informed that it was found to he a useful practice in 

 marine and stationary boilers, to create a disturbance in the currents of air 

 passing tlirough the flues, for the purpose of mixing up the particles as 

 much as possible; and a similar advantage might probably be obtained by 

 mixing the air in the tubes of locomotive uoileis. 



Mr. GiBDONS said, he had observed a similar advantage fron". mixing the 

 particles of air in beating the air for his blast furnaces near Dudley ; the 

 pipes through which the air was passed for the purpose of heating it were 

 bent like a syphon, so as to cause all the particles of air to come in contact 

 with the sides of the pipes, and the air was found to be heated much more 

 efiiciently by these bent pipes than by straight pipes. 



Mr. Allan said, he had tried an engine with a J-inch iron rod fixed in the 

 centre of each tube; the rods were as long as the tubes and supported at 

 intervals by short projecting pins to hold them in the centre of the tubes. 

 The engine had been worked with them for some time between Birmingham 

 and Liverpool, but no difference was found in the working and consumption 

 of coke, as compared with the same engine doing the same work without 

 the rods in the tubes ; the result was found to be exactly the same in 

 both cases. 



Mr. C. CowPER remarked that the rods in the tubes would bare the effect 



