310 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



rooT. 



and at the same time to have the same engine power ; and there may be a 

 variety of other circumstances. For instance, on the Nurfulk railway : at 

 present the connection is not completed of the two railways at Norwich on 

 account of a bridge of an original construction, a swin^ bridje ; su that 

 the Csh is brought from Yarmouth to Norwich, then discharged, and car- 

 ried across the river, then loaded again, and then brought to London, and 

 those trucks go back light. Therefore, if you were to take the actual cost 

 of the locomotive power for the goods there, you would have to charge 

 two miles of locomotive power for one mile of effective traffic, and conse- 

 quently, although the locomotive engines might be running at actually a 

 less mileage than another line, yet in that sort of comparison, they might be 

 made to appear to be working at a greater cost. Therefore, unless you 

 have all the circumstances brought before you, any comparison of that 

 nature appears to be not conclusive. 



It does not appear that very much higher rates of speed would be re- 

 quired. There would be much more convenience from giving frequent 

 departures, than from running particular trains at a very high velocity. 

 And there is another question ; after you have attained a speed of 40 or 45 

 miles an hour, the saving of time by the increase of speed does not go on 

 ;)i'o rata ; it is very much diminished. You save a great deal of time by 

 an increase from 20 miles an hour to 40 miles an hour ; but an increase 

 from 40 to 50 miles an hour is not of that importance. With the present 

 permanent way, where the rails are 70 to 75 lb. weight, you might travel 

 certainly at 70 or 80 miles an hour. 



The repairs are very much augmented by bad curves, and a wide car- 

 riage, or a wide engine, must be subject to greater torsion from curves than 

 a narrow one. Cannot believe that it is possible that the repairs of the 

 wide gauge carriage and engines can be so little as of the narrow. Has 

 no experience of the repairs on the wide gauge, but on a bad curve line the 

 repairs are very much augmented. On the Newcastle and Carlisle, the 

 repairs of the engines, as compared with the North Shields, are about £250 

 per engine per annum. 



Has a return of the performance of a goods engine in ordinary working 

 on the Alidland line between Derby and Kugby ; and whether you take it 

 as the actual weight moved or the evaporating power, it stands a favour- 

 able comparison with any engine referred to in the evidence of Mr. Cooch. 

 In one trip the engine took from Kugby a gross load of 348 tons IG cwt., 

 to which you would have to add herowu weight and that of her lender, 

 about 35 or 30 tons. She took that load up 16 feet a-mile from Kugby, 

 and she acquired a velocity for that 16 feet a-mile, of 15 miles per hour. 

 If you compare that with a level line, it is equivalent to a gross load of 

 very nearly 700 tons on a level. The quantity of water evaporated on that 

 length was 35^ gallons per mile; that is equal to about 100 feet per hour. 

 Now, from ihe experiments it appears, and it is consistent with one's no- 

 tions, that the power of evaporation is directly, or nearly so, as the power 

 of blast, that is, the number of strokes per minute, and the volume of that 

 blast. I'rom a return of an experiment on the Northern and Eastern, an 

 engine which, at 30 miles au hour, evaporated not more than 70 or 80 feet 

 per hour, evaporated 150 feet at 50 miles per hour. 



[Mr. IJidder here assumes that the resistance to a train of 348 tons, on 

 a gradient of 16 feet a-raile, is the same aS that to a train of 700 tons on a 

 level. The conclusion is independent of the velocity, and seems derived 

 from taking the resistance of friction at 7 or 8 lb. per ton. This calcula- 

 tion omits the pressure on the blast pipe, which is a function of the velo- 

 city, and the resistance of the air, which is nearly as the square of the 

 velocity, and depends, moreover, not on the weight of the train, but on the 

 surface exposed to the action of the air, 15ut setting all this aside, the 

 amount of 7 or 8 lb. for friction is not even approximately correct, for it is 

 certain that resistance from the unevenness of the rails, he, is much greater 

 at high than at low velocities. The idea that " the power of evaporation 

 is directly or nearly as the power of the blast," is contradicted hereafter 

 by Mr. Bidder's own figures. Besides, if this theory were true, no water 

 at all would be evaporated when the engine was standing still, for then the 

 blast is not in action.] 



On the last experiment the train was reduced to 72 tons 12 cwt. gross, a 

 little more than half the first load. The net speed realised was 43 miles 

 ]>er hour, and the quantity o£ water evaporated was at about tile rate of 

 190 feet per hour. Tliis engine was a lung tube engine ; the tubes are 13 

 feet long, 15 inch cylinders, 22 inch stroke, 5 feet G inch wheels ; the area 

 of the lire-box is 49 7S0 feet, and the heating surface of the tubes 738 ft. 

 Then the letter from which I take this goes on, — "To prove the tempera- 

 ture of Ihe heat in the smoke box I suspended four pieces of metal, viz., 

 one piece three parts tin and two pai'ts lead, one piece one part tin and 

 four parts lead, one piece lead, and one piece zinc, their melting poiuts , 

 respectively being 33 1^ 470'', 59'J°, and GSO^". Tliese metals being sus- 

 pended immediately above the top row of the tubes, about one inch from 

 the tube plate. I fouud at the end of the journey ihat the three first-men- 

 tioned metals had melted, but the zinc did not melt in any of the three 

 trips, proving the temperature of the heated air to be about 691)°." Now 

 that shows that the temperature oV the stcaiu iu the boiler being about 

 312', and the air, when escaping from the tubes, being about COD°, it is 

 quite clear that every part of those tube; must have been available in 

 heatiug the water, and in the evaporation of steam ; and by a comparison, 

 taking the different loads and comparing them with tlie experimiuls of the 



goods engines, which are of a similar construction, with the same area o 

 fire-box, and the same tube surface, you will find, as nearly as can be, that 

 the evaporating power is a function of velocity, and also the funclioa 

 of the area of the cylinder. This clearly shows that the long boiler not 

 only increases the evaporating power, but increases the economy in the 

 conversion of water into steam. 



["This clearly shows" nothing of the kind. To get at anything like a 

 trustworthy conclusion, Ihe same experiment should have been made with 

 a short-boiler engine, and the results compared. We are not told who 

 made the experiments, or how they were made, and consequently do not 

 know how far they deserve to be trusted. Our confidence, by the by, is 

 not increased by reading that the fact the zinc did not melt proves " the 

 temperature of the heated air to be about 600°" ; this makes well for Mr. 

 Bidder's side of the question, but all that can be legitimately concluded 

 is, simply, tnat the temperature was under GSO°— it may have been 670°. 

 The fact that the temperature of the air was about double that of the 

 steam, shows that not nearly all the heat of the former was usefully ap- 

 plied. To economise the whole of it, the hot air must continue to act on 

 the steam till it can impart no more heat to it — that is, till the temperature 

 of both is the same. How c.-»n we tell, a priori, that if the experiment 

 had been tried on a short engine, this result would not have been more 

 nearly attained than with the long-boiler engine, especially if we are to 

 conclude that "the evaporating power is a function of velocity and also 

 the function of the area of the cylinder," and does not depend on the 

 amount of heating surface. It is to be observed the words, " is a function 

 of," are incorrectly used as synonomous with " is proportional to."] 



"In those experiments are you well assured that there was no priming ? 

 — Yes, especially in the goods engine ; because, if you take that particu- 

 lar experiment to which I have alluded, where she took 385 tons gross up 

 16 feet a-raile ; if you take the area of the cylinders and see what quantity 

 of steam must h^ve passed through them in passing over that gradient, 

 and see what was the volume of the steam at the requisite pressure to con- 

 vey that train, you will find that the quantity of water is more than that 

 which appears to have been consumed, which I attribute to the fact that 

 they must have been using steam at rather a higher pressure than ordinary 

 iu the boiler. 



" How did you ascertain the amount of evaporation ; after the experi- 

 ment was over, how did you ascertain the quantity of water? — They take 

 the gauge of the tender, and the gauge in the boiler, aud theu they have 

 the superficial area of the boiler at the different heights, and the area of 

 the tender. It is ascertained with very great exactness, and great fa- 

 cility." 



[Here Mr. Bidder assumes his proposition in order to prove it. He 

 takes it for granted lhat there would be no priming, in order to show that 

 there was none. First, wilh respect to the means of ascertaining the 

 amount of evaporation : his method simply shows the quaniity of water 

 got rid of — not the amount converted into steam and usefully employed. 

 The water mijht have passed away by leakage or priming,* or the steam 

 might have escaped by the safety valve. But he is assured these contin- 

 gencies could not have occurred, for he calculated the amount of work 

 done, and the quantity of steam required to do it. He is certainly the 

 first person who has been able to ascertain the resistance to a train with 

 anything like the accuracy necessary fur a calculation of this sort, and has 

 increased the simplicity, If not the accuracy, of his operations by taking 

 it for granied that 700 tons on a certain gradient are equivalent to 348 on 

 a level. To find the quantity of water required to do the work, the recipe 

 is to "take the area of the cylinders and see what quaniity of steam 

 passed through them," but who but Mr. Bidder could tell a /in'ori how 

 much that steam was dilated iu coming from the holler, and what was its 

 precise etlect when acting expansively — in other words, the exact nature 

 of its mechanical action ? Both problems are, considered separately, so 

 intricate as to baffle all human ingenuity. The first, the resistance oflered 

 to the train depends on the wind, concussion at the joints of the rails, fric- 

 tion of Ihe axles of the carriages, and other complicate mechanical actions, 

 varying with every variation of velocity. The second, the mechanical 

 efliijct of the steam it is equally impossible to predict. The relation of the 

 power of the steam lo Ihe quantity of water used depends on the tempera- 

 ture and tension in the boiler and the temperature and tension iu the 

 cylinder ; the latter varying not only at every stroke, but (when the steam 

 is used expansively) at almost every part of the stroke. It is therefore 

 quite impossible to take the two problems separately ; they must be con- 

 sidered together, as De I'ambour has considered them. We have quite 

 suflicient proof, however, that Mr. Bidder's calculations were all wrong, 



* Pe Pambour shows ttiat of the whole quantity of water consumed, one-fourth is, on 

 the average, wasted by being drawn into the cyliiuiers in a liquid stale. So Diuch lor 

 there bdng no priming 1 



