1846.] 



THE CIVIL ENGINEEERAND ARCHITECT'S JOURNAL 



311 



from his anomalous conclusion that mure water was required than was 

 actually expended ! In accounting for this anomaly, he let us into a se- 

 cret;— he confesses that he did not know the pressure in the boiler, 

 which of course should have been an essential ingredient in his calcula- 

 tion.] 



A law seems to exist that the power of producing steam is as the velo- 

 city, that is, the number of blasts and the volume in the cyliniier; that is, 

 as long as the fire-place will supply you with combustion to that amount ; 

 but as you increase the blast the combustion goes on in that ratio ; and 

 eveu with the Great Western experiments, and those taken with a short 

 boiler, it is found almost invariably as the result, that 1 lb. of coke evapo- 

 rates 7 lb. of water. With the long boiler we hardly ever get an effect of 

 less than 8 lb. of water to I lb. of coke, and in some of these experiments 

 it is as much as 10 lb. And we get economy in another way. In a com- 

 parison of engine power and of the consumption of coke, you may get a 

 fallscy from not knowing to what extent there may be pilotage in one line 

 or another. If an engine on one line has double the amount of engine 

 piloting which there is on another, her consumption goes into the general 

 mileage ; whereas the consumption of coke while running may be very 

 much less. On Ihe Northern and Eastern, when that line was 6rst opened 

 to Broxbourne, their engines only consumed 20 lb. of coke while running, 

 and yet the daily returns showed 36 lb. ; that was from llie quantity burnt 

 at the stations. Now a long-boiler engine is economical in tliat respect, 

 because, no doubt, from the length of lubes, the quantity evaporated whi!e 

 standing and the coke consumed is very much less ; in fact, an engine with 

 13 feet tubes burns only half the coke standing that is consumed by an 

 engine with 8 feet 6 tubes. 



[In the first part of this paragraph the blast is supposed to increase the 

 evaporation, but to also increase the consumption of coke in ihe same raliu; 

 so that though more coke is burned in a hour, the effect of each pound of 

 coke is not increased. In other words, the blast is supposed not to increase 

 the economy in the use of the coke. Now, it has always hitherto been 

 supposed that a strong current of air (and, therefore, of oxygen) rendered 

 the combustion not only more rapid but more perfect also, and that where 

 the supply of oxygen was insufficient, a great part of the fuel was wasted 

 and passed away unconsumed, or without developing its evaporative 

 power. It is, therefore, concluded that the rapidity of the current of air 

 (within certain limits, of course,) increases the actual economy in the con- 

 sumption of, fuel. In the last sentence of the paragraph, the "quantity 

 evaporated while standing" by a long-boiler engine is supposed to be less 

 than by a short boiler engine ; and yet the principal argument in favour of 

 the long boilers has always been understood to be their increased amount 

 of heating surface, which mig ht be supposed to increase the quantity of 

 water evaporated, whether the engine were standing or in motion.] 



" Do you lliink any good would result from the use of corrugated metal 

 for fire-boxes? — I do not think there would be any. They get apparently 

 a larger surface ; but I think the effect upon that surface must be weak- 

 ened to the same extent as >oh happen to extend the gauge. With a cer- 

 tain amount of combustible matter in a pound of coke, if you get the 

 whole of that out, which we do with a long-tube engine more eB'ectually 

 than they do with a shorter one, from the fact that we get 8 lb. of water 

 evaporated instead of 7 lb., I do not see myself how you can do more than 

 extract that matter and apply it usefully ; it does not matter whether it is 

 in the fire-box or in the tube." 



[Mr. Bidder does not see any use in increasing the surface of the fire- 

 box, because " you can do no more than extract the matter and apply it 

 usefully." But, then, that is assuming that all the matter is applied use- 

 fully in the long-boiler engines ; whereas, he himself has proved that this 

 is not the case, from the fact that the temperature in the tubes is twice 

 that of the steam.] 



There is a great dilference of opinion respecting the atmospheric resist- 

 ance ; the fact has come before me from the experiments not only with the 

 locomotive engines but on the atmospheric railway, where I see the power 

 that has been expended and the result, and I cannot account f\tr the ex- 

 penditure but by atmospheric resistance, or some resistance which is a 

 function of the velocity. For instance, I false a locomotive engine. No. C, 

 on the Northern and Eastern. I put behind that engine a tiain of 100 

 tons, she will travel with that train at the pace of 30 miles an hour, and 

 she will evaporate at the rate of 80 feet per hour. I reduce those 100 

 tons to 20, that engine goes at 50 miles an hour and evaporates at the rate 

 of 150 feet per hour ; and I find, as nearly as can be, that the same quan- 

 tity of water is converted into steam per mile with the light train as with 

 the heavy train, showing that the pressure ujio'i the pision is nearbj the 

 same, and that the power has been absorbed by this great augmentation of 

 resistance. 



[The blunder marked by italics rivals the celebrated notion started in 

 the investigation of the Norfolk railway accident {ante page .^1), that au 

 engine can be forced off the rails by the suddenly shutting off tlie steam. 

 lu the present case, Mr. Bidder evidently disregards the fact that the 

 quantity of water drawn into the cylinder in a liquid state is much 

 greater at high than at low velocities. Otherwise, how could he conclude 



that, because the same quantity of water was consumed during a slow as 

 during a fast journey, the cylinder-pressure was the same in both cases.' 

 It is impossible to estimate Ihe effective vaporisation by the water con- 

 sumed; for even the mere circumstance of the boiler being fuller at one 

 time than another will account for an enormous increase of priming. The 

 inconsistency of this paragraph with that in which Mr. Bidder states that 

 he is "well assured there was no priming" is also to be noted. There he 

 was able to calculate Ihe resistance to the train with the utmost exactness ; 

 all language of uncertainty was avoided, — we were told to " see" the 

 resistance of a train in passing over a certain gradient, as if this seeing 

 were the easiest process in the world. }lere, however, the resistance is 

 treated in quite a difl'erent manner — it is some very vague uncertain thing, 

 which Mr. Bidder " cannot account for" but by supposing there is "some" 

 force or another (he knows not what) functional of the velocity. Here, 

 too, Ihe resistance can only be ascertained from the vaporisation. There 

 it could be calculated independently of the vaporisation — aye, and with 

 that precision that Ihe amount of priming could be deduced from the cal- 

 culation. It is important to observe that at ordinary boiler pressures, 

 steam occupies/rom/o«r iofite humh-cd times Ihe space of the water from 

 which it is produced. This shows how enormously the evaporation is 

 exaggerated by neglecting the effect of priming.] 



The following are extracts from Mr. Bidder's report on the results of 

 the experiments tried with the broad and narrow gauge engines : — 



" Before calling your altention to the facts shown in these experiments, 

 which cannot be influenced by any circumstances, and which, in my opin- 

 ion, are alone worthy of your notice, I will repeat that the object proposed 

 was to ascertain the truth (and that alone) of statements which had re- 

 spectively been made by Mr. Gooch and myself, as to the comparative 

 power and economy of engines now in operation on Ihe broad and narrow 

 ■raune lines, and more especially with respect to the importance of surface 

 obtained by increasing the fire-box, or lengthening the tubes, and that any 

 inference drawn from the results which shall bear on the merits of Ihe two 

 fauces will be foreign to the objects proposed, and false, as Ihe circum- 

 stances of the experiments are not found to obtain in practice. Supposing, 

 however, that they were, and that an in increase of power were deemed 

 desirable, I do not hesitate to say that that which is at present found 

 ample for all purposes might be doubled, or more than doubled, on either 

 "aufe.* 1 shall now proceed to examine Ihe evaporating power of Ihe en- 

 gines, as well as the relative economy of evaporation and eflicient application 

 of the' steam evaporated. It will be recollected that on Ihe part of Ihe broad 

 "anoe, it was alleged (in reference to the statement Ihat on the narrow 

 gauge, not only economy but power was obtained by lengthening Ihe 

 boiler) that the area of the fire-box alone was Ihe test of the power of the 

 locomotive engine, and that 2 cubic feet of water per hour per superficial 

 foot of fire-box have the capacity of evaporation of locomotive engines ; 

 and thus it was alleged, that the Great Western engines could evaporate 

 nearly 200 cubic feet per hour, while the narrow gauge engines could only 

 convert into steam 100 cubic feel, the comparative fire-box surfaces being 

 as 97 feet to 50 feet. In order at once lo lest this principle, let us examine 

 Ihe facts shown in the experiments. By reference to the particulars of Ihe 

 experiment with 50 tons with engine A, on December 31st, 1845, between 

 Darlington and York, a distance of 88^ miles, it will be found that the 

 water evaporated is 20.520 lb., being at the rale of 232 lb. per mile. In 

 the (up) journey the fir:>t mile, as well as the last 1-}, were passed over 

 slowly ; as also were the first quarter and last mile on the return trip, in 

 all 3i mile>i. In order, therefore, to get at the maximum a\erage rale of 

 evaporation on Ihe trial, I take 20,250 lb., less 812 lb. (the water consumed 

 in passing over the above Sj miles, at llie rate of 232 lb. per mile), 19,700 

 lb., the weight of water evaporated by the engine in passing over the re- 

 maining 85 miles, which was eliected in lOG minutes 12 seconds, being at 

 the rale of 11,150 lb., 178 cubic feet per hour. I will now compare ihis 

 with the experinii nt most resembling it iu regard to the evaporatmn tried 

 on the broad gauge. I lake Ihe experiment with CO tons on December 

 17lh. The total water evaporated was 24,0-10 lb. on 100 miles, or 232 lb. 

 per mile ; deducting from this 1,041 lb. for water due to H miles passed 

 over slowly, leaves 22,596 lb. of water evaporated in 112 minutes and 42 

 seconds, being at the rate of 11,820 lb., 189 cubic feet per hour, that is 

 little more than the evaporation of the narrow gauge engine. When, how- 

 ever, we compare Ihe coke, we find in Ihe case of the broad gauge engine, 

 that 7'8 lb. of water only were converted into steam by 1 lb. of coke, 

 whilst the narrow gauge engine evaporated 96 lb., being a difference lu 

 regard to economy of fuel of 23 per cent, in favour of Ihe narrow gauge 



engine." ^ 



* " In evidence given by Mr. Goucli, the average gross weiglit of passenger trains on 

 some or" tile principal railways is given as follows : — 



Great West- 

 ern Railway 



Average gross 

 iu tons . . 



iveight 



Granfl Junc- 

 tion Railway. 



London and 



Birmingham 



Railway. 



Birmingbaro 



and Gloster 



Railway. 



42 



38 



South West- 

 ern Railway. 



SB 



The lightest of the trains included in the above average .ire express trains,- theie are 

 now, therefore, engines in use on both gauges cn-pable of taking trains ot double lUe 

 weight of those required in practice ol the expiess speeds." 



