1850] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



135 



in part, it accords with the opinions we have expressed; and, in 

 part, it gives a tone and colouring to our observations, not justified 

 by the statements we have made. Divested of extraneous matter, 

 Messrs. Joyce and Co. candidly acknowledge to the following: — 



That it was with their entire sanction and approval, our contem- 

 poraries asserted that in engines constructed by them, the 

 consumption of fuel is less than S lb. per horse-power per hour; 

 vhi/e, under tlie old si/xteni, it is ahotit 12 lb. 



That the Smyrna Steam Flour Mills had not, been put to work 

 in this kingdom (which, of course, is what we expected) — there- 

 fore, that the given rate of consumption, per horse-power per 

 hour — erinal to 3 lb., as above — was not the result of experimental 

 tests made with those engines, but of other steam-engines made 

 by the firm. 



That they do not profess to have made any new or important 

 discovery in the principle of double-cylinder expansion (nor did 

 we suppose that they had contemplated making any such profes- 

 sion, notwithstanding their assumption to the contrary): — they 

 state, therefore, all that they claim is, the simplification of the 

 arrangements by which the number of parts, the weight of the 

 material, and the amount of workmanship, are proportionably 

 reduced; and, by which, there is a decrease in the cost of con- 

 struction, and a diminution of friction, vis inerticB, and momentum. 



Messrs. Joyce and Co. acknowledge, that we are "quite right" 

 in the statement we have made, that the double-cylinder system 

 is, for pumping purposes, inferior in elfect to the single-cylinder 

 engine; and they append the following remarks: — "There is not a 

 question that single-cylinder expansion, if the load can duly be 

 proportioned to the efl^ect of the steam, from its first impact on 

 the piston to its minimum of effective attenuation, tri/t produce a 

 greater absolute impulse, or, as it is termed, a better duty, for the 

 volume of steam consumed, titan if the medium were a double- 

 cylinder." 



After these candid admissions, there are but few difl^erences of 

 opinion between Messrs. Joyce and Co. and ourselves. Those dif- 

 ferences, however — few though they be — are of such importance, 

 practically, that we must be permitted to make some comments. 



Corroborative of the correctness of their statements, as to the 

 superior yield of power by double-cylinder expansion, by a given 

 consumption of fuel, over single-cylinder expansion, Messrs. Joyce 

 and Co. bring to their aid some statements, published by us, in the 

 Journal for April, 184-2. 



We feel much indebted to the Messrs. Joyce, for having drawn 

 our attention to that article, published by us so far back as eight 

 years ago. Messrs. Joyce and Co., however, in making reference 

 to that article, have made an ex parte statement. They have, in 

 that instance, and in others, when alluding to our remarks, shown 

 more ingenuity than ingenuousness, by making it appear that our 

 observations are as they could wish them to be, rather than as what 

 they are. In illustration, we will make a few extracts from the 

 paper published by us in 1842, which will develope a wonderful 

 coincidence of opinion as entertained by ourselves, and impart 

 quite a dift'erent cliaracter to the remarks we made, than what the 

 extracts made by Messrs. Joyce and Co. would have a tendency to 

 impress. Those e.xtracts are as follows: — 



" A certain quantity of the power which an engine exerts is exerted in 

 overcoming its own friction, lifting the water wliich has accomplistied the 

 condensation of the steam out of a vacuum, &c. Tlie term, horse power, is 

 used to denote the available quantity of power which an engine is capable of 

 furnishing for any useful purpose, and is, therefore, the excess of the power 

 produced, over the power consumed by the engine itself. Any estimate of 

 the power of an engine, based on the assumption that the whole power 

 exerted by the piston is the true measure of the engine's beneficial exertion, 

 is, therefore, fallacious. An allowance of one-eighth of the power as being 

 consumed by the engine itself, is a usual and moilerate allowance. 



" The amount of economy to be obtained from steam working expansively 

 is precisely the same, whether the expansion takes place in one or two cylin- 

 ders. The use of two cylinders serves to equalise the action, and to dimi- 

 nish the strain thrown upon the moving parts ; but it is questionable, whe- 

 ther the greatest fluctuation of pressure, when only one cylinder is used, 

 Wight not be rendered equally instrumental in the production of a regular 

 motion, simply by using a larger fly icheel, or driving the fly-wheel at a 

 greater velocity; and whether it is not guile as simple to increase the strength 

 of the moving parts a little, as to add an additional cylinder and piston, to 

 prevent them from being subjected to so great a strain." 



Again : — 



" In common rotative engines, which operate without expansion, the ordi- 

 nary consumption of coal is 10 lb. per horse-power per hour. But the horse 

 power" (of an engine, practically) "is usually found to be about 52,000 lb. 

 raised one foot high, in a minute, which is equivalent to 26-208 millions 

 raised one foot high by a bushel of 84 lb. of coal. Some good engines, 



however, operate with an effective pressure upon the piston of 13Jlb. per 

 square inch = 00,000 raised one foot high for a horse power ; and a few 

 ascend as high as 66,000 per horse power, nithout employing high-pressure 

 steam. The engines consume about 8 1b. of coal, per nominal horse power, 

 or 4 lb. of coal per horse power of Watt. The consumption of coal, in this 

 engine" (the Messrs. Rennie's, or the Pimlico engine) "is 1323 lb. per hour 

 j^.-yf = 2-5 lb. per horse power, per hour." 



In the preceding extracts, it will be perceived that we have 

 made a marked, and an unerring distinction, between the nominal 

 and the actual duty of steam-engines, and the quantities of coal 

 consumed in either case; and that we have stated the average 

 consumption of coal, in the best engines, to he 8 lb. per horse- 

 power per hour when estimated on the nominal, and 4 lb. when 

 estimated on the actual power. And we have further qualified 

 our statements, with respect to the duty of Messrs. Rennie's 

 engine, by stating that wlien, for the actual duty of the single- 

 cylinder engine, the consumption is 4 lb. per horse-power per hour, 

 it is at times when the steam is not expanded, and not at high 

 pressure, both of which, when combined, would reduce the amount 

 of fuel as usually consumed. 



These statements are very different to those made with the 

 expressed sanction of Messrs. Joyce and Co., which make it appear 

 that their engines consume less than 3 lb. per horse-power per 

 hour, ^^ while engines under the old system consume about 12 lb.;" and 

 which, as it was likely to mislead the public, called forth our 

 remarks and animadversions. If 12 lb. per horse-power per hour 

 he given on the iiominal power of the single-cylinder engine, so 

 also ought the 3 lb. on the double-cylinder. It ought, also, to be 

 borne in mind, that the consumption of fuel, as given by Messrs. 

 Joyce and Co., is for double-cylinder expansion, with high-pressure 

 steam, and for single-cylinder non-expansion, with steam of low- 

 pressure — a statement much in their favour. AV'e therefore cannot 

 accord with the final observation in the Messrs. Joyce's letter, 

 "that the double-cylinder system must prove by far the most 

 economical as regards fuel." Nor can we give our sanction to the 

 statement made by them, that we have very pro])erly shown that 

 it is so. Our opinions, as published in 1842, and those recently 

 avowed, forbid any such interpretation of our thoughts, and are 

 diametrically opposed to any such construction of them. 



The 'Treatise on Mechanics,' by Dr. Olinthus Gregory, is in the 

 libraries of most engineers ; therefore, the merit due unto Horn- 

 blower, and the controversy between him and Messrs. Boulton and 

 ■Watt, are well known. Still, as Woolf brought the double-cylin- 

 der engine into practical operation, it is customary with practical 

 men to denominate such construction, the " JJ^oolf-cngine." In the 

 article to which Messrs. Joyce and Co. have referred, as published 

 by us in 1842, we have given unto Hornblower his full meed of 

 praise for that invention. We think, therefore, it is scarcely fair 

 of Messrs. Joyce and Co. to assume that we were ignorant of the 

 matter, with tliat article before them. In the jjapers of several of 

 our contemporaries on the Smyrna Steam Flour Mills, which 

 appeared with the express sanction of the Messrs. Joyce, and 

 which we reviewed in our last number, it is called the " Woolf-en- 

 gine," not the Hornblower ; therefore, out of deference to them, 

 and to public opinion, we gave unto the double-cyliuder-engine its 

 usual denomination. 



Messrs. Joyce and Co. must pardon us for giving an unqualified 

 contradiction to their construction of our statement, "that single- 

 cylinder expansion is very commonly adopted in cotton-spinning." 

 AVe said nothing of the kind. What we did say was this: — "Mk 

 expansive system is now very commonly adopted to rotatory fly-wheel 

 engines by our best engineers; and we ourselves were principally 

 instrumental to its Jirst adaptation to the delicate processes of the 

 cotton manufacture." Our language, therefore, will not admit of 

 any such twisting. We are aware that Mr. MacNaught, as stated 

 in our last number, and that highly eminent firm, Messrs. Ben- 

 jamin Hick and Son, of Bolton-le-Moors, Lancashire, are re-intro- 

 ducing, with certain modifications, the double-cylinder expansive 

 engine, and applying it to cotton-spinning processes. But we 

 must be permitted to entertain the opinions we avowed in 1842, 

 and reiterated in our last number, as to the relative merits of the 

 Watt and Woolf steam-engines, until we be furnished with data of 

 the most unquestionable kind, as to the superiority of the latter. 



In concluding, we must state our opinion tliat, although we 

 differ from them in opinion, and they have, in some instances, 

 given a tone and colouring to our statements not warranted by 

 facts, we tliink much merit is due to Messrs. Joyce and Co., as 

 constructive engineers and makers of steam-engines, and for the 

 candour of their present communication. — Ed. f ^.E. & A. Jouk.nal. 



