1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



21 



PROCEEDINGS OF SCIENTIFIC SOCIETIES. 



INSTITUTION' OF CIVIL ENGINEERS. 



" On the ylctimi of Steam as a Moving Pou'er in the Cortxish Single Pmiip- 

 ing Engine." By Josiah Parkcs, M. Inst. C. E. 



C Continued fi-om page \ 16, Vol. HI.) 



Mr. WicKSTEF.D beiiis called upon by the President, ileclineil at jiresent 

 giving an opinion upon tlie tlieory before the meeting. He stated, that he 

 was still trjing experiments npon the engine at Old Ford — that the results 

 up to the present time were in accordance %vith his anticipations — that, with 

 small screenings of Newcastle coals, the duty of the engine amounted gene- 

 rally to 75 millions, and sometimes to as much as 81 or 82 millions. He 

 thought that 7 ft. per square inch for friction and imperfect vacuum was too 

 large an allowance for an engine of the size of that at Old Ford, as, when the 

 speed was 10 or 1 1 strokes per minute, the jiower was equal to 200 horses, 

 and, if an allowance of or 7 lb. was made, it would be equal to 100 horses' 

 extra power, which he felt certain could not he correct. At the same time, 

 he believed that in ver)' small engines the amount of friction, cic. might be 

 correctly estimated at 6 or 7 M>. per square inch. He had also tried some 

 experiments upon a Boulton and Watt low-pressure engine : by the intro- 

 duction of Harvey and West's patent pump valves, the duty of the engine 

 had been increased from about 281- to .32-1 millions. He was now trying ex- 

 periments on clothing the cylinder, &c., and with steam in and out of the 

 jacket : the result of all these experiments shoidd be laid before the Institu- 

 tion as soon as they were completed. 



Mr. Seaward considered the paper to be very valuable, as opening a new 

 \iew of the action of steam, and inducing discussion and experiment ; but he 

 was not prepared to aUow at once the percussive action, nor could he admit 

 it to be the cause of the increased duty, as, if so, an augmentation of pressure 

 in the boiler would give a corresponding increase of duty. Engines were 

 worked at all pressures up to 60 ft., and even higher; but it was not per- 

 ceived that the highest pressure gave the best results. He attributed the 

 increase of duty to an improvement in the manner of using coal under the 

 boilers ; to the use of good non-conducting substances for clothing the cylin- 

 ders, steam-pipes, &c., to prevent the radiation of heat ; and to the genera! 

 improvement in the construction of the valves and other parts of the engines, 

 the proper dimensions for which were at present better defined. The expan- 

 sive principle did not seem to have operated so well in the rotary as in the 

 pumping engines. He liad not hitherto credited the statements of engines 

 ■working with a consumption of coal of 5 lb. per horse power per houi, nor of 

 the great advantage of the use of steam at high pressures. Several Scotch 

 boats had been worked v\1th steam, at a pressure of 33 lb. on the inch, with- 

 out any corresponding advantage. The increase of duty, then, he attributed 

 to other reasons than the etfects of percussion, as, independent of other con- 

 siderations, the steam must always have possessed the same percussive force, 

 which it must have exercised without producing the effects now attributed 

 to it. 



Mr. Wicksteed observed, that there were many reasons wliy the duty of 

 the double expansive engines in Cornwall was not in proportion to that of the 

 single pumping engines. The introduction of the former only dated from 

 about the year 1834 ; but few had been made ; there had not been the same 

 amount of experience to guide the engineer in their construction ; they were 

 of small size, and consequently the amount of the friction was greater in pro- 

 portion than in the large single pumping engines. Notwithstanding all these 

 disadvantages, the duty had increased from 15 or 20 milUous to 57 millions. 

 It had been stated that the double expansive engines constructed by Hall 

 and by Penn did not consume more than 5 tb. of coal per horse power per 

 horn- ; while the ordinary low-pressure double engines requii-ed from 8 tb. to 

 10 tb. of coals. He would suggest to such members as possessed the power 

 of verifying this fact to communicate their observations to the Institutiou. 



Mr. Rendel would direct the attention of members to the main feature of 

 Mr. Parkes's paper, wliich was the discoveiy of the action of a percussive 

 force by the steam. The full investigation of this subject deeply interested 

 the scientitic world : and it was important that its merit should be clearly 

 displayed. If any power could be gained from the percussive action, the 

 more suddenly the steam could be admitted upon the piston, the more ad- 

 vantageous would be the result. It would be interesting to learn whether, 

 in the changes in Cornish engines, from which such improved duty had re- 

 sulted, any increased ai-ea had been given to the steam pipes and valves, and 

 to what extent as compared with the old practice. If any change of this 

 kind should be found to have taken place, it would be an argument in favour 

 of the percussive principle. 



Mr. Field expressed his sense of the ohUgations wliich the Institution owed 

 to Mr. Parkes for having taken up this subject. It had been supposed by 

 many persons that, independently of the economy arising from clothing the 

 cylinder, jacket, and boilers, and the expansive action of the steam, some 

 other cause might have assisted iu producing the increase of effect in the 

 Cornish engine. Doubtless, much had been done to economise heat and 

 steam by the slow combustion of the fuel under the boders, by diminisliing 

 radiation, and by expansive action. Nevertheless, the question to be solved 

 was, Can these improvements account for the whole progressive advance in 

 the duty from 40 or 50 to 90 millions ? He trusted that Mr. Wioksteed 



would apjjly the indicator to his engine, and ascertain the pressure on the 

 piston at every portion of the stroke. 



Mr. Parkcs remarked, that many observing men had conceived doubts of 

 the sufficiency of the commonly-received theory of expansion to explain the 

 excessive economy of the Cornish above the unexpausive engine. Some had 

 recorded this opinion. Mr. llenwood found the steam's force in the Huel 

 Towan engine unable to sustain the water-load alone. Messrs. Lean showed 

 a similar deficiency of steam power in an engine at the United Mines ; and 

 Mr. G. H. Palmer was perfectly correct in his statement, that the absolute 

 force of steam as commonly appreciated was inadequate to the performances 

 assigned to it : hut he was wrong in asserting that these effects had not r)eeu 

 obtained, for they were indubitable. 



.\s doubts hacl been expressed with regard to the accuracy and sufficient 

 duration of the experiments selected as the basis of his analysis, he would 

 state, that Mr. Henwood obtained the quantity of water consumed as steatn, 

 during a continuous observation of twenty-four hours, having previously mea- 

 sured the water discharged by a given number of strokes of the feed pump, 

 and then cotmting the entire number of strokes made to supply the boilers 

 during the experiment. The pump was used periodically, and its whole con- 

 tents injected into the boilers at each stroke, so that no material error could 

 arise as to the quantity of water constmied as steam. With respect to the 

 resistance overcome, Mr. Henwood several times measured the whole height 

 of the lifts in the most careful manner, not comprehending the fact of the 

 steam's force being unequal to sustain the load of water alone. Not content 

 with this, he measured the water discharged by the pumps, aiid found a near 

 correspondence with the calculated quantity. 



Mr. Parkcs would prefer a short experiment on the consumption of water 

 as steam to a long one, as more likely to be accurate. He had rejected the 

 eight months' experiment on the United Mines engine, as being unsuitable 

 for the purpose of his investigation : for, during so long a period, the boilers 

 must have been several times emptied and cleaned, stoppages must have oc- 

 curred, condensation, leakage, aud other circumstances must also have taken 

 place, which unfitted that experiment for analysis. Long experiments were 

 the best for the practical determination of the duty done by coal ; but the 

 action of steam in performing that duty was altogether a separate considera- 

 tion. The consumption of water as steam for a single stroke of the engine, 

 if it could be obtained, would be all-^ifficient for investigating its action in 

 the cylinder, as the weight raised by a Cornish engine must be the same at 

 every stroke. If any error existed in the statement of the wated evaporated, 

 it was more likely to be in excess than in deficiency ; for it would he admitted 

 that the conversion of lOi tb. of water into steam, by 1 lb. of coal was not a 

 common occurrence. Yet, granting this result to have been obtained, it ap- 

 peared that there was not steam enough to overcome the resistance. Such 

 was the result of the analysis of the Huel Towan and Fowey Consols engines, 

 for which the evaporation was ascertained ; and if less water had been con- 

 verted into steam, the deficiency of power, compared with the effect, would 

 necessarily have been still greater. Mr. Henwood's statement of the per- 

 formance of the Huel Towan engine was confirmed by a previous trial of the 

 same engine in 1828, conducted by a committee of twenty-one competent 

 persons, when it appeared, after twenty-six hours' experiments, that 

 87,200,662 ft. had been raised one foot by a bushel of coals. Mr. Henwood's 

 experiment gave 8l,398,!)00 ft., so that in the analysis the lowest result was 

 used. 



It had been urged, that if any such force as percussion belonged to steam 

 now, it always formed one of its properties. This was true ; but it either 

 may not have been well appUed, or its effect not detected. The expenditure 

 of power as derived from the quantity of water consumed as steam could not 

 be determined so long as any condensation of steam took place in the cylin- 

 der ; for whatever steam was there condensed had lost its power. The per- 

 fect clothing of the Cornish cylinders rendered the analysis of the action de- 

 rived from a given quantity of water as steam nearly free from error. 



Mr. Wicksteed had stated, that when he kept the steam out of the jacket 

 of one of Boulton and Waft's engines, it required fidl steam throughout the 

 stroke to overcome the load ; whereas, with steam in the jacket, some expan- 

 sion could be used. This would show a greater expenditiure of power in one 

 case to produce an equal efi'ect. Such, however, could not be : an equal 

 power operated in both cases ; but iu the one, a portion of it was annihilated, 

 or had produced no useful effect. 



Mr. Parkes considered it as demonstrated, that a force, independent of the 

 steam's simple elastic force within the cylinder, did operate in the Cornish 

 engines. The term percussion might be objected to when appUed to an elas- 

 tic fluid. Neyertheless, he conceived that the instantaneous action trans- 

 mitted to the piston, on the sudden and free communication efiectcd between 

 the cylinder and boiler, must produce an effect analogous to the percussion 

 of solids. He considered the proofs of such action adduced in his paper as 

 irresistible. 



He would ask how it could be accounted for that the steam was in a state 

 of expansion during 19 out of 20 parts of the stroke in the Huel Towan en- 

 gine, as shown by the indicator diagram, though it was freely admitted during 

 one-fifth of the stroke, unless a velocity had been given to the piston by an 

 initial force exceeding that of the steam's simple elastic force ? How was it 

 that, at the end of the stroke, the steam's elasticity was able to sustain so 

 small a portion of the load in equihbrio, unless a momentum had been trans- 

 ferred to the mass by the impact on the piston, and aided the expanding 

 steam to complete the stroke, which alone it was incompetent to perform ? 



