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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



153 



two ilitterent curves in two different dirt'ctions, there is evidently a 

 great omission aomewliore, wlncli, liovvcver, we might I'orgivc if hU 

 uieaviing could be discovered, but it cannot. A little further on he 

 tells yon to join a m, h in, c m, &e., but where the point la is to be 

 placed, Mr. jS'icholson has quite forgotten to say. 



Page 10, referring, as is stated at the head of the page, to plate 

 21, is another example in which, from the type being completely at 

 variance with the plate, we are left quite in the dark as to what the 

 author wishes to communicate. 



The practical part of this work, if, indeed, any ])art may be so 

 called, is scarcely less defective than that of which we have already 

 spoken; the direction for dividing the face of the arch into stones of 

 imequal thickness is unworkmanlike and unsightly, and where brick- 

 work is used, the joints must necessarily be larger on one side than 

 on tlie other. 



On the whole it must be admitted that the book is far from being 

 worthy of the great reputation ilr. Nicholson lias hitherto justly ac- 

 quired ; it has the appearance of being got up by his junrneymen, and 

 signed with his name without a sufficiently careiul revision. But we 

 have said enough, though, in closing the book, we cannot but express 

 a wish that, before he had sought the mote in his brother's eye, he 

 had removed the beam from his own. 



Maiicksler. W. H. B. 



March 2(i, 1810, 



MARINE ENGINES. 



Employment of the expansive principle lo iln full extent in Marine 

 Engines, /vith a saving vf hulf the fuel. 



Sir — In my remarks in your Journal of last month I dwelt at some length 

 on the advantages to be derived from the employment of the Cornish 

 double beat valve in marine engines, esjiecially the facility which such 

 afford of working the steam expansively. But it may be asked why 

 all this talk of working expansively where there is little or nothing to 

 expand ? I wouKl answer this question by another : why adopt a good 

 plan by halves '. take the Cornish boilers also, or a suitable modifica- 

 tion of them, and raising the steam to 35 lbs. ellective, carry out the 

 ))rinci|)le of expansion to its full extent; this would at once reiluce 

 the consumption of coal one half, and s<j double the range of our steam 

 navigation. On such a startling proposition as this being mooted, the 

 question naturally suggests itself, how has Ibis so long escaped the 

 first men of the day i That I shall not attempt to answer; it is sutli- 

 cient that it has escaped them, and a very slight examination of the 

 malter will make this evident. 



Thus taking the horse power at 33,000 lbs. lifted one foot per minute 

 with a consumption of 8 lb. of coal per hour, and tliis is below the 

 average consumption, we get a duty of 23,000,01)0 (though 20,000,000 

 would be nearer the mark, especially in steam boats). 



If any be disposed to assert that this is overstated as regards the 

 Great Western and British Cjueen, as these vessels are said not to 

 consume above six or seven pounds per horse power per hour, I an- 

 swer, the Queen's engines are fiOO horse power at 15 strokes per 

 minute, or the piston travelling through 220 feet per minute, now the 

 pressure of steam, &c. reniaining the same, the power exerted by the 

 engine is exactly as the space through which the piston travels ; but 

 12 strokes per minute is nearly the average number the engines make, 

 as appears by her log; this reduces her power in the ratio of 13 

 to 12, and increasing the consumption of fuel per horse power in 

 an equal ratio, makes the six or seven pounds nominally consumed 

 equal to S or 'J. 



Whereas many of the Cornish double acting crank engines used for 

 stamping ores, the most trying work an engine can possibly be sub- 

 jected to, and where there is greatest loss by friction, are doing a 

 duty of 50, 56, and even 60,000,000, as appeals from the authenticated 

 reports of the engineers. 



Although tfiis will not be doubted by any one who has had the op- 

 portunity of seeing the engines at work, it may suit some to doubt and 

 even to deny the truth of these reports ; so they did those of the 

 pumping engines doing a 70 or SO,OUO,000 duty ; but as 'JO, and eveu 

 100,000,000 is now being done under their eyes, what credence can 

 such men expect for any statement they may in future make. 



Having had occasion to visit Cornwall some three years ago on 

 business, immediately after having completed the engines of a large 

 vessel now on the London and Dublin station, the easy valves, the cool 

 engine room, and almost smouldering fires of the Cornish engines, as 

 contrasted with the stiff and heavy slides, the suffocating heat of the 

 engine room, and roaring furnaces I had just left, attracted my parti- 

 cular attention; and though possessing at that time no data beyond 

 the published reports of the engineers, I saw enough to convince ma 



of their immense superiority, and at once set about considering how 

 the same plan could be carried out in marine engines, a point which I 

 hope to be now able to make clear, and the objections to which I shall 

 endeavour to deal with in detail. 



The first is the increased danger of explosion or collapse supposed 

 to be occasioned by the great density of steam. 



The second is the additional strength required in the engines to 

 withstand steam of such density wdien first admitted into the cylinders. 



The third is the increased weight of the boilers, and the extent of 

 flue surface required for their successful application. 



Tlie first objection, the increased danger, I shall begin by denying 

 " in toto," nay, it appears to me that there is absolutely increased 

 safetj', for the following reasons : 



Setting aside the increased weight, &c., one boiler can be made 

 quite as capable of supporting a pressure of 35 lbs. as another is of 

 supporting 3 lbs.; the safety valves would have much less tendency to 

 stick fast under the higher pressure, and their becoming a little stiff, 

 or two or three pounds overloaded, would not be of the slightest con- 

 sequence on a boiler calculated for a pressure of 35 lbs., though it would 

 have a very dangerous tendency on one calculated for 3 lbs. 



But the great argument for increased safety is this : it is an estab- 

 lished fact that with boilers of the usual construction, nine-tenths of 

 the steam boat accidents occurs through collapse of the overheated 

 flues, much more than from any excessive pressure of steam in the 

 boiler; nor is this to be wondered at if we consider how the fires are 

 urged. Now with the Cornish boilers and a proper system of expan- 

 sion, the same work can be done vvith half the coal, and if we consume 

 only half the coal on the same or a greater extent of fire bar and flue 

 surface in a given time, tlien it follows clearly that we have a fire of 

 only one-half the intensity, and the risk of collapse from overheated 

 flues diminished in like jiroportion. But if these arguments are in- 

 sulUcieut, then the following fact is greatly in their favour, viz., tliat 

 as few if not fewer accidents occur in Cornwall wliere such boilers are 

 in universal use, than in any part of the kingdom where steam power 

 to a like extent is used; and if it be further true, as I have heard 

 stated both in Cornwall and elsewhere, tflat many of the Cornish en- 

 gineers will eng.ige to keep up the boilers for ever, for tlie annual sum 

 of 5 or 6 per cent on their original cost,* such an argument appears to 

 me, as it will to most practical men, to be at once perfect and con- 

 clusive. 



I now come to the increased strength required in the engines, and 

 this on examination will appear trifling. To commence then with the 

 paddle-wheels as they remain of the same size, and are driven at the 

 same speed, no alteration is required in them, and of course the same 

 remark will apply to the paddle-shafts through which the power is 

 transmitted. I'liese being subjected to no increased strain as the 

 average effective pressure upon the piston which takes place when 

 the piston is half stroke, &c., and the crank at its point of greatest 

 torsion, is the same as in a common engine. The intermediate shaft 

 alone with its cranks, in which the crank pins nve/ast, requires addi- 

 tional strength, and as this shaft is only about one-sixth the length of 

 the two padd'e shafts, and the strength of a shaft increases as the cube 

 of its diameter, the increased weight will be trifling: next there is the 

 top frame that carries this shaft, and the bottom frame supporting the 

 gudgeons and columns, the strength of both must be increased, and it 

 is as the square of their depth ; next comes the piston rod, this will 

 do as before, the piston rod of a large engine being equal to 20 times 

 the strain it is ever subjected to : the same remark will apply to the 

 malleable iron columns supporting the top frame, as each of them is 

 usually made of the same strength as the piston rod. 



The piston must lie strengthened, but the cylinder will do as before, 

 as it is strengthened at the extremes where the greatest pressure of 

 the steam is by its flanges, and in ordinary cases we are under the ne- 

 cessity of making it much stronger then necessary to ensure a sound 

 casting, and also to support the framing attached to it ; besides a 

 cylinder of three-fourths the capacity is sullicient for the same power, 

 so here we are positive gainers in two most important points, strength 

 and space. The gudgeons of the cylinder of double the strength will 

 not be stronger nor heavier tlian the main centres of the beam engine 

 of the ordinary construction must necessarily be. 



The points" then which require increased strength are, the inter- 

 mediate shaft and gudgeons, the top and bottom supporting frames, 

 and the piston. The increased weight from this cause would not ex- 

 ceed G or S per cent, beyonil that of the same description of engine at 

 the ordinary pressure, and after taking this into account, the total de- 

 crease, by adopting the vibrating cylinder, would be at least 25 per 

 cent. 



I now come to the question of increased weight in the boilers, and 



" Perhaps some of your readers can affirm or contradict this. 



