August 2, 1894] 



NATURE 



329 



It dealt especially with one feature in the boiler which has been 

 invented by the author. This steam generator, it will be remem- 

 bered, consists chiefly of three horizontal cylinders arranged, in 

 cross section, in the form of a triangle. Two of the cylinders 

 are placed in the wings of the furnace, whilst the third, which 

 is above, at the apex of the triangle, the fire-grate forming the 

 base. The top cylinder is connected to the two wing cylinders 

 by two series of curved pipes, which are so arranged as to 

 deliver into the top cylinder at its upper part ; they thus deliver 

 above the water-level of the boiler, which is about half-way up 

 the top cylinder. Connecting the top cylinder with the two 

 wing cylinders, respectively, are two external pipes ; the whole, 

 of course, is enclosed by a smoke-jacket, and the steam genera- 

 tion occurs in the connecting pipes. The method of working 

 of the Thornycroft boiler is as follows : — The heat from the fur- 

 nace playing on the pipes or tubes, which connect the top cylinder 

 to the two wing cylinders, causes generation of steam, the flow 

 of which is upwards. As is nearly always the case when 

 steam is generated in small pipes, a great deal of water is also 

 carried upwards with the steam. This water is delivered into 

 the top cylinder, and from thence is free to flow downwards to 

 the two wing cylinders, from whence it can rise again through 

 the generating tubes, and so on in continuous cycle so long as 

 there is water to be evaporated. The success of a water-tube 

 boiler in practical working may be said to be dependent on its 

 circulation, so that when rapid evaporation takes place, and 

 water is quickly driven away from the heating surface, other 

 waler should be there to flow in to take its place. Mr. Thorny- 

 croft has always claimed that this circulation is mo5t effectually 

 attained by having the steam-generating tubes deliver in the 

 upper part of the top cylinder. The principle has been ques- 

 tioned, and in order to set the matter at rest experimentally, 

 the author had made a boilerpurelyon hissystem, and alsoonein 

 which the design was so modified as to bring the generating 

 tubes into the top cylinder below the water surface. If we have 

 I made our explanation clear, it -^ill be seen, as stated by the 

 I author, that in either boiler, pressure in the lower vessel is that 

 I due to the full depth of water in the boiler, in addition to the 

 steam pressure, and reduction of density in the generating tubes 

 will be available for causing circulation ; whilst reduction in 

 pressure in the wing cylinder below that due to the head of 

 I waler in the boiler, will reduce the circulation. In fact, the \ 

 circulation of water in the boiler is governed by variations of 

 pressure. In order, therefore, to measure these variations, Mr. 

 Thornycroft had recourse to a water gauge connecting the top 

 and bottom cylinders, the height of the column of water 

 showing the greater or lesser pressure in the wing cylinder. 

 , The results of the trials were shown by a diagram in which 

 I curves were assigned to each series of experiments. When the 

 j steam-generating tubes were arranged as in the normal Thorny- 

 j croft boiler, as the rate of evaporation increased, the height of 

 the water in the gauge-glass showed a steady and comparatively 

 small pressure in the wing cylinder. Thus, when the evapora- 

 tion was increased from 3 lb. to 20 lb. per square foot of heat- 

 ing surface per hour, from and at 212° Fahr., the fall was about 



2 inches of water. With the boiler having tubes delivering 

 below the water-level when the evaporation was raised from 



3 lb. per hour per square foot of heating surface to about 

 15 lb., the fall in pressure in the wing cylinder was from 

 3 inches to 7 inches, roughly. Thus it will be seen that the circu- 

 lation of water in a boiler of this class, where the tubes deliver 

 above water-level, must be more energetic than when the tubes 

 deliver below water-level. In both of these experiments, what are 



I called the down-comer tubes, that is to say, the two tubes at the 

 ends of the cylinders provided for completing the circuit ofcircu- 



j lation, were in use. The utility of these tubes has, however, 

 been questioned, and in order to throw light on this point, Mr. 

 Thornycroft next m.ade a series of experiments with a boiler in 

 which the tubes delivered below the water-level, and the down- 

 comer tubes were out of use. The results were interesting 



i and instructive. The reduction in pressure in the wing cylinder 

 was extremely rapid as the evaporation increased ; after a time, 

 however, the curve reached its lowest point, and then suddenly 

 bent upwards, showing an increase in the pressure. This last 

 phenomenon Mr. Thornycroft attributed to the fact thit thesteam, 

 instead of rising uniformly in the tube, as it would when the 

 evaporation was moderate, was driven out at the lower end ; 

 and this, of course, would tend still more to check the circula- 

 tion. The diagram is well worthy of study on the part of those 



NO. 1292, VOL. 50] 



interested in any class of boiler design, and it may be found in 

 the Transactions of the Institution. 



In the discussion which followed the reading of this paper, 

 the most interesting feature was a description, by Mr. Pilcher, of 

 the device used by Mr. Maxim in making the boiler of his flying 

 machine. This boiler, it may be stated, is a marvel of lightness. 

 It is a Thornycroft boiler with very small generating tubes 

 about \ inch in diameter ; it is said to have given off steam 

 equivalent to 300 I.H. P. at a pressure of 300 lb. to the square 

 inch ; the weight of the boiler itself being but 3 lb. per I.H. P. 

 With the small diameter tubes it was found impossible to keep 

 up circulation suflScient to prevent the destruction of the boiler, 

 and, in order to aid the natural circulation, Mr. Maxim intro- 

 duced what may be described as injector circulation. He 

 carried the feed-pipe of the boiler into the down-comer tube, 

 covering the orifice of his feed-pipe by a conical valve, which 

 was attached to a long spindle, and, working through a stuffing- 

 box, was carried outside the pipe. The valve was kept closed 

 by means of an external spiral spring, so adjusted as to give a 

 pressure of 50 lb. to the square inch on the valve. The feed- 

 pump naturally would overcome this additional pressure, so that 

 the pressure in the feed-water on the boiler side of the pump 

 would be 50 lb. above the boiler pressure, and thus 350 lb., the 

 boiler pressure being 300 lb. It will be seen, therefore, that, 

 on the hydraulic pressure opening the valve, the feed-water 

 would be injected with some velocity into the boiler, and thus 

 would set up a circulating current. In this way it was found 

 that the boiler in the flying machine could be made to work 

 very perfectly. 



Prof. Biles, in his paper, described a method by which he 

 proposed to transform mail steamers into war vessels in the 

 event of hostilities. Details were worked out by the author, and 

 given in the paper ; but into these we need not enter. The 

 most noticeable feature was a long recess in the side of the 

 ship, into which the author proposed to pack an armoured belt 

 when the vessel was required to take up its warlike role. 



The scope of Mr. Denny's paper is described by its title. Mr. 

 Morrish, of the Admiralty, in the discussion which followed, 

 gave a formula used by Mr. Froude at Ilaslar, which appeared 

 to us even more simple than the method described by Mr. 

 Denny. We must refer our readers to the Transactions for these 

 formulae. 



Mr. Gross gave details of certain trials made with the 

 system of burning fuel in steam boilers, referred to in the title of 

 his paper. A very good result in regard to economy of fuel 

 was obtained with one vessel referred to ; the consumption 

 being I '3 lb. per I.H. P. per hour of .South Wales coal for the 

 main engines. We fail to see, however, in what respect 

 " suction " draught differs from " forced " draught in regard to 

 economy. .\s Sir Edward Harland humorously stated in the 

 discussion : "If one wishes to remove a person from a certain 

 position, it does not much matter whether one gives him a pull by 

 the nose, or applies pressure from behind." There may, of course, 

 be some occult virtue in "suction" as compared to pressure, 

 but we certainly have never heard it satisfactorily accounted for. 



The last paper was read by Mr. Terry. It is remarkable how 

 those tank steamers which carry oil in bulk may be freed from 

 the insidious vapours which always arise whenever a little of 

 these hydrocarbon oils are present. Mr. Terry tells us— and 

 he is confirmed in this by Mr. Martell, Lloyd's chief surveyor, 

 who has naturally had thorough opportunities of seeing these 

 matters in practical work — that, in the same spaces that have 

 been occupied by petroleum, rice, and other perishable food, 

 cargoes have been carried without detriment. So successful 

 have the results been, that it is now proposed to carry even tea 

 in these tank steamers. 



We cannot deal with the many pleasant excursions that were 

 really the leading feature of the meeting. The proprietors of 

 the various mail steamers, the London and .South-Western 

 Railway Company, and those gentlemen who had estates in 

 the neighbourhood, seemed to vie with each other in enter- 

 taining the members of the Institution. On Friday morning 

 a visit was paid to Portsmouth Dockyard, where many 

 interesting features were shown by Admiral Fane, the super- 

 intendent, and the oflicers of the permanent staft". In the after- 

 noon an excursion was made round the Isle of Wight, on board 

 the Fredcrica, a vessel of 1509 tons, and about 6000-h.p. , 

 which had been lent by the London and South-Western Rail- 

 way Company for the purpose. 



