352 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Not. 



ettimaliog the power of the engines is similar in form to that of Tredgold, 

 and tbe cylinder pressure is deduced from the boiler pressure by a meiliod 

 independent of the omitted element : that is, the calculation proceeds on 

 the assumption that the boiler pressure and cylinder pressure will bear a 

 constant relation to eacli oiher, whatever may be the rate of evaporation. 

 This assumption, Ue I'anibour, in his Treatise on ihe Steam Eugine, has 

 shown to be erroneous, and he contends therefore that the whole ofTrcd- 

 gold's Theory of the Steam Engine is incorrect, and that his formula; for 

 computing the power of engines can never be correct, except by an acci- 

 dental compensation of errors. — The views of De Pambour are now gene- 

 rally adopted by scientific men. We>vill venture at the risk of appearing 

 to dilTer in some measure from the very high authorities by whom the re- 

 ports before us are sanctioned, to apply De Pambour's method of calcula- 

 tion to one or two of the results of the experiments just described. 



In tlie report duted .January 31 (p. 3), we find the following comparison 

 of two experiments : — 



Total l)oiler pressure per square inch 

 llevolutiona of engine per minute 

 Fuel consumed per minute 



It is assumed in the report that until the steam was cut off the cylinder- 

 pressure was the same as that of tlie boiler. On Ue Parabjui's princi- 

 ple, however, the conclusion would be very different. In absence of more 

 accurate data we may suppose that since the form and dimensions of the 

 bailer, &c., were identical in the two experiments each pound of coals 

 evaporated effectively the same volume of water (M). Then 



Expt. (1). 

 ■ill M 



Expt (2). 

 •2016 M 



Cubic feet of water evaporated per minute 

 Now it appears from the table in De Pambour's Treatise on Locomotive 

 Engines (p. 00), that steam at 922 lb. pressure occupies 310 times the 

 volume of the water from which it is produced, and steam at 03 79 lb. 

 pressure occupies about 414 times the space of tbe water from which it is 

 produced. Therefore in ibe present case 



Expt. (I). Expt. (2). 



Cubic feet of steam evaporated per minute 4iiMx316l 2010 M x 444 -t 



= 14536 M / -8;(6I M / 



The capacity of the cylinders was the same in both eases ( = N), but in 

 the first experiment the steam was cut off at one-third of the stroke, in the 

 second at one-half of the sti'oke, consequently taking] the number of revolu- 

 tions of the engine per minute in each case, we have 



Expt. (1). Expt. (2). 



Cubic feet of steam admitted to cylinders per minute 33.''XiN\ 44'4ri x ^ N •» 



"17 83N i -•22-225N / 



Comparing these quantities with the volumes of steam generated in the 

 boiler, we see that in experiment (1) 11530 M cubic feet of steam at a 

 pressure 922 lb. were dilated to occupy 17 83 N cubic feet: and in ex- 

 periment (2) 8951 M cubic feet of steam at pressure of 03-79 lb. were 

 dilated to occupy 22 223 N cubic feet. But by Mariotte's law the pres- 

 sure of steam is inversely as the space occupied. Hence 



Bolter pressure 



Cylinder pressure 



Expt. (1). 



17-83 N 



14536lu 



Expt. (2). 

 _ 22-225 1>I 

 "825 1 M~ 



2 2-225 X 14536 

 17-83 X WjI 



' X 2-0208. 



Hence we get finally the following relation : 



Cylinder pressure (1). Boiler pressure (1). 



Cylinder pressure (2). Boiler pressure (2J, 



_ Boiler pressure (1). 



Builer prebsure (2J- 



Showing that the proportion between Ihe cylinder pressures before the 

 steam is cut off, instead of being equal U) the proportion between the boiler 

 pressures will be more than double lliat jiropurtion. This certainly seems 

 to show the importance of taking into consideration the relative generation 

 of steam in the boiler and consumption of it in the cylinder. 



Let us take another case — the trials 5 and in the second report of 

 which the experimental results are given above. Adopting a method of 

 calculation exactly the same as the foregoing, and considering that in the 

 .S'/icnn'r and McLane the cylinders were of the same size, that the steam in 

 both was cut oil' at half-strol^e, and lliut by De Pambour's table steam at 

 68-7 lb. occupies 480 times, and steam ai (i2-7 lb. occupies 150 times the 

 vtilume of the water producing it — we have 



1-27 



Total pressure In boiler 



Revolutions per minute 



Fuel consumed per minute 



Culiic feet of water evaporated per minute 



Cubic feet of steam evaporated per minute 



Cubic feet admitted to cylinder per minute 

 Cylinder pressure 

 Boilt-r pressure 

 Hence we get the relation 



Cylinder i)re3sure (McLane) Boili 



Cylinder pressure (Spenser) Boili 



Boiler pressure (McLane) 



Boiler pressure (Spencer) 

 That is Ihe proportion of the cylinder pressures before Ihe sleam is cut 

 off is not thiit of the boiler pressures, but upwards, of one-fourth more. 



The actual relation of the boiler pressure to the c\linder piessure in each 

 engine is immediately ascertained by giving M and N their proper values 

 — that is, by substituting the size of the cylinder, and the evaporative 

 effect of each pound of coke. It would however generally be more accu- 

 rate to ascertain the total quantity of water evaporated during the trial, 

 and make a correclioa for priming according to the method detailed by Da 

 Pambour. 



We are indebted to the courtesy of an American correspondent for copies 

 of the reports alluded to. The source from which this favour comes, and 

 the very flattering manner in which it is conferred, greatly enhance its 

 value, and induce us to hope that notwithstanding differences of opinion 

 between American and English engineers, we shall have hereafter further 

 opportunities of recording the investigations of our transatlantic fellow la- 

 bourers in tbe advaucement of practical science. 



METROPOLITAN SEWAGE MANURE. 



The select committee, which was appointed last session to consider 

 sundry plans for Ihe appiicaiion of the sewage of the metropolis to agricul- 

 tural purposes, reported in favour of the Aletropolitan Sewage Manure 

 Company Hill, which has since passed into a law, with certain modifications. 

 They declined to recommend its postponement or rejection for the sake of 

 Mr \i'icksted's plan, for cairying olf the entire sewage of London, in a 

 tunnel of fioin eight to twelve feet in diameter, and at a depth of from 40 

 to 80 feet under the level of the streets, being of opinion that tlie first ex- 

 periment of dealing with sewage water had belter be tried upon a smaller 

 scale and at a less formidable exoense ; and, as regarded .Mr. Hig.;s' plan, 

 they conceived that the public miuJ was not at present prepared to risk 

 the establishment of any such reservoirs as he proposed lo construct, al- 

 though, by the precautious he contemplated, he would prolialily preclude 

 the possibility of any deleterious or offensive consequences. It appeared, 

 indeed, that the main ground of complaint against the bill by the owners or 

 occupiers of land was, that power had been taken in it to couotruct reser- 

 voirs or tanks for the reception of stagnant and oll'ensive sewage water. 

 That power was, in consequence, relinquished by the promoters. The 

 committee, however, seemed to concur in the propriety of such a step out 

 of deference to public feeling only, being of opinion tint the loss of such a 

 provision would, in some degree, impair the elhcienry of a measure which 

 proposed at all tunes to remove from the Thames Ihe daily-increasing re- 

 fuse of Loudon. As explained by Air. Smith, of Deanston, llie operations 

 of the company are lo be limited lo the Kind's .Scholars' poiiil sewer — the 

 contents of that sewer to be received in a well coiisiructed for the purpose, 

 thence to be raised by steam-engine pumps, and carried by a main pipe 

 about eleven miles in the direction of Egliani, wiUi branch pipes to the sur- 

 rounding farms ; the distribution of which, however, will depend much 

 upon private arrangement. When nsetl for irrigation, Ihe liquid is lo ba 

 discharged from one of these .service pipes into the channels usually em- 

 ployed for that purpose; when applied to tillage laud tlie service pipe is 

 to lie brought to some convenient tlistanc e in the licid, there tocoinmunieale 

 with a hose made of canvas, and capable of being elongated and conveyed 

 to particular spots, from whence the water may be thrown by a Jet over as 

 extensive a surface as Ihe pressure upon the pipes will admit — that pres- 

 sure being derived from a stand-pipe about two feet in diameter, and 150 

 in height, the eiilire distribution lo be conducted by the servants of the 

 company, with a view to its proper control, aided by an ailjuslmeut at Ihe 

 steam-engine, to indicate the quantity of ivaler taken at Ihe extremities, so 

 that Ihe speed of the pumps may be diminished or increased accordingly. 



The company expect that Ihe farmers will hud it Iheir interest to allow 

 it to be used exclusively for irrigation durii.g ihe night and during the day 

 by jet and otherwise, so as to equalize tiie supply iu the 24 hours, and 

 prevent the waste which would otherwise occur iu the absence of reser- 

 voirs. Looking, however, to the dilhculties that usually alteiid a lirst ex- 

 peniueut, and to provide for extiaordiuaiy Hoods, means are to be adopted 



