1840.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



127 



Fist. 2. 



4 9 4 5 4 2 4-0 3 8 3 6 34 

 Average 3 08 lbs. ]}ei: circular inch. 



3i 2 8 



tngi-ther with an abridged extract from a report of an liulic.itor ex- 

 periment made by him on one of Bonitun and Watt'.s old 10 horse 

 engines, now working in a cotton factory in Afancliester', and also 

 including some remarks thereon vTllich seem pertinent to the subject 

 of iriy last letter. 



i'his engine has a cylinder 31i inches diameter, 7 feet siroke, and 

 a speed of 260 feet a iidnute. The diagrams were taken by Atac- 

 naught's Indicator, the scale of which is ^ of an inch to each pound 

 per square inch of pressure, or, which is the same thing, -^78.54 of a 

 ]ioniKl per circular inch, the latter is the scale used, as it greatly 

 abridges the calculation. Fig. 1 was taken when tlie whole of tile 

 machinery was at work in the usual way, and being uieasiired, it gives 

 an average for the gro.ss pressure of 11"_'S It)s. per circular inch. 

 Fig. 2 was taken when the whole of the machinery was thrown ofT, the 

 load of the engine then consisting only of the friction of the shafts, 

 gearing, and straps running on the loose pulleys, together with the 

 power required to work the engine itself. This figure, being mea- 

 sured, gives an average pressure of 3-98 Itjs. per circular inch, for the 

 friction of the engine, shafting, &c., which, deducted from the gross 

 pressure, leaves 7-3 His. per circular inch for the net effective jjressure. 



The velocity of the piston, 260, drawn into the area of the cylinder, 

 3l-.=>-, (=00-2'25 circular inches,) =257,985, and this number, divided 

 by 33,0U0, gives 7-S horse power, for each ]iound pressure per circular 

 inch. This, again, multiplied by the nett effective pressure as above 

 found (7-3 fts.J gives nearly 57 for the "nett effective indicated horse 

 power" then exerted by the engine. 



Tlie following remarks are extracted from Mr. B.'s report: — "The 

 power consumed by the shafting unloaded seems enormous, but as 

 there is an immense cpiantity of it, and a number of the steps, I am 

 told, are not in very good order, and tlie straps, too, being probablv 

 very tight, I am inclined to think that the result given by the imlicator 

 diagram is not far from the truth. This result, which is usually called 

 acailabk power, means all the power that is exerted by the engine, 

 exclusive of what is absorbed by the engine, shafts and straps; but it 

 would be a mistake, however, to suppose that all this available power 

 is delivered (so to speak) at the machine pulleys, for as the work is 

 put on, the friction is increased through all the ramifications of the 

 shafting, and the amount of this increase, which we have no means (jf 

 ascertaining, must be deducted from wliat is called the available 

 power, if we wisli to know the amount of power consumed by tlie 

 inachimry alone. It is a good practice, however, to debit the ma- 

 chinery, not only with the power consumed by itself, but also with the 

 ])ower required to overcome the increase of friction along the shaft- 

 ing, and this I have done, calling them together available power. It 

 is not a good term, and another wants substituting in its jjlace. It is 

 manifest, therefore, that a great quantity of shafting shonid be avoided, 

 both on account of the power lost in turning the shafting itself, but 

 also on account of the increased increase of friction when loatled," 



The following is a list of the machiucry, as furnished by the mana- 

 ger of the works : — ■ 



4 Pair of Nhiles, 648 spindles each. 

 1 Pair ditto 1080 ditto 

 8 Thjostles 180 ditto 



164 CaUco Looms, 120 picks a minute. 

 60 Double Carding Engines, 50 inches cacb. 

 3 Drawing Frames, 14 rollers each. 

 6 Dyer's Frames. 

 1 Willow and Lap Machine. 

 Winding and M'aqnng. 



1 Mechanics Shop with Lathes and Grindstone. 

 63 Tape Looms, 25 pieces each, 



1 1 Braiding Machines, 



2 Tape Callenders. 



1 Winding .Machine. 



2 Latlies and Grindstone. 



Besides the above, there is a 9 inch pump 28 feet deep, which is includcil 

 ill the engine and .shafting friction. 



The remarks of Mr. Bowman bear evidence to the necessity of a 

 nicer distinction in the technical terms used re3|)ectiiig the power of 

 steam engines than has generally been admitted bv engineers, and 

 nhich necessity it was ])artly the object of my last letter to point out. 

 The above list of machinery will also, I hope, be useful to mechanical 

 engineers or others, who take an interest in the statistics of the steam 

 engine. But I must observe that this engine must by no means be 

 taken as an average specimen of the factory engines in Manchester; 

 for as regards ecomuny of steam, and consequently economy of fuel, it 

 is considerably below that average, hidced, I believe a worse case 

 will not be easily found in any regular factory in Lancashire; and this 

 is, in fact, one reason why I have selected it," for the serious conside- 

 ration of those advocates of the expansive system who are continually- 

 boasting that the engines in Cornwall are doing five or six hundred 

 per cent, more work for the same quantity of fuel than is done in any 

 other part of the kingdom ;* and also in order that there shall be no 

 longer any mistake in this matter. Let any Cornish or other engineer 

 point out clearly, how, even so little as 50 per cent, more work is to be 

 done by the steam that the above engine uses, or a saving of one third 

 of the fuel, and I kuuw the owner of the engine will be very much 

 obliged to him. 1 can firiii many factory owners that would be very 

 glad to save even 10 per cent, in fuel at the ]n-esent time, in addition, 

 of course, to the orilinary interest of money for the capital required to 

 be expended in adopting the improvement. 



In the town of Manchester, owing to the difficulty of getting a suHi- 

 cieucy of cold water, the steam-engines are generally doing a much 

 less duty th in iu the cottou-factory district surrounding if, where it is 

 not unconiinon to find tliem using about 6 pounds per horse per liour 

 on the effective, or 9 lbs. on the nett effective indicated power. The 

 diagram Fig. 3, wliich was sometime ago given me by my friend Mr. 



Fitr. 3. 



3 cA 



3 



* In a Cornish newspaper now before me (called " Lean's Ivigine Reporter 

 and Advertiser,") lor Novouiler, 1839, is inserted an extract from the Athe- 

 n.Tenm, in which it is slated " that/cc times as much work lias been done by 

 a Cornish steam-engine as hy an crcellent l^nulton and Watt's engine on Ihe 

 common system ; or thai Ihe same amount of work is done willi one fifth 

 part of the expense (if fuel ! A statement almost incredible, yet perfectly 

 true." It is, indeed, '• alni'ist incredible " to me, that the respected authors 

 of the Monthly lleports shgulJ allow such assertions to pass withuitt note or 

 comment. 



S 2 



