1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



15 



Y: 





I" -Iqi 



1 2 (j g r 



e n+ 1 



« + l 

 e —1 



we obtain definitively for the value of the frictiony, 



h' + h" Y 



/= 



r + TY 



We have been involuntarily led, by the ingenuity of this method of 

 eliminating the resistance of the air, into giving a complete sketch of 

 the calculation, but we do not think it more than sufficient to give an 

 adequate notion of its nature aiid perfection. 



The fourth section contains an account of 12 experiments made on 

 tlie above prhiciple on the Whiston inclined plane on the Liverpool 

 and Manchester Railway, with trains consisting of different numbers 

 of wagons and variously loaded, the results of which are collected in a 

 table at page ICl. 



From these experiments, the mean friction of the wagons, taken in- 

 dependently of the resistance of the air, amounts to -^ of their gross 

 weight, or to 5'7(J lb. per ton ; but to simplify the calculations, M. de 

 Pambour takes it at Gib. per ton, which makes -^ of the weight of 

 the wagons. He remarks, however, that, except in cases of extreme 

 velocity, the resistance of the air may be computed with regard to the 

 wagon of greatest section alone, according to Borda, taking the fric- 

 tion then at 7 lb. per ton. 



Chap. VI. treats of the Gravity on Inclined Planes, and Chap. VII. 

 of the Pressure produced on the Piston by the action of the Blast-pipe. 

 This is a very important point, and requires much more experience 

 and careful investigation, in which the results of experiment are com- 

 pared with the laws of Natural Philosophy, before it can be considered 

 as satisfactorily settled. In comparing the last column of the Table of 

 Experiments, page 193, with the last but one, we find some great dis- 

 crepancies, although the coincidence is in some cases perfect or nearly 

 so. For example, we find the pressure on the piston due to the action 

 of the blast-pipe, 



Out of 38 observations given in the table, the last ten of the above 

 selection present the nearest accordance with the numbers calculated 

 by M. de Pambour's formula, while the first 12 exhibit discordances 

 too great to permit us to consider that formula as confirmed bv the ex- 

 periments alluded to. We must, however, content ourselves with 

 these determinations for the present, for want of more accurate data, 

 but we hope the invesgation will not be allowed to rest here, since the 

 theory of the Steam Engine is not complete without it. 



This chapter concludes \s\t\ia^ pracUcal table of the pressures against 

 the piston, due to the action of the blast-pipe, which furnishes the means 

 of taking this effect into account in some degree, which is better than 

 neglecting it altogether. 



In chapter VIII. the friction of the engines, both unloaded and loaded, 

 is very ably investigated, and illustrated by experiments, and in chap- 

 ter IX. is ascertained the definitive resistance per unit of surface of 



the area of the piston resulting from the various resistances estimated 

 in the precedirg chapters. 



In chapter X. are presented the details of 22 experiments on the 

 vaporization of locomotive engines, together with an inquiry into the 

 circumstances which influence the rate of vaporization, which tends to 

 prove, Istly, that this is not affected by (the load on the safety-valve) 

 or pressure of the steam formed, 2ndly, that it increases with the velo- 

 city of the engine, all other circumstances being the same. The 

 author even goes so far as to conclude from those experiments which 

 bear on this point that the vaporization of locomotive engines varies 

 very nearly as the fourth root of the velocity. We do not feel justi- 

 fied in adopting such a law on the strength of so few experiments, 

 which do not all concur even in establishing the general truth. That 

 the velocity of the motion does influence the vaporization we are not, 

 however, disposed to doubt; we only wish to intimate that more, 

 numerous experiments must be made on the subject before the law of 

 that influence can be deduced. 3rdly. it is shewn from the experi- 

 ments, three of which were made without the blast-pipe, that this 

 appendage to a locomotive engine increased its vaporization more than 

 five-fold, but that the narrowing more or less of the orifice of the 

 blast-pipe produced no very remarkable result. It appears, however, 

 that a certain area or orifice produces a maximum effect for each en- 

 gine, th It area being for the Star engine, according to ihe experi- 

 ments here reported, about 3-13 square inches. 



In the 5th section of this chapter, which treats of tlie comparative 

 I'aporizaiion of Ihe fire-box and the tulns, and of the dejiiiite vaporization 

 of the engines per tmit of heating surface of their boilers, the author 

 asserts, page 270, that, " during the active working of engines of a 

 construction similar to that of the experiments, the two portions of 

 the boiler vaporize, per unit of surface, the same quantity of water." 

 This equality is ascribed to the fact of the flame being drawn, by the 

 force of the blast, through the whole length of the tubes, by which 

 means the whole of their surface is exposed to radiating caloric, but 

 there are probably other circumstances which tend to equalize the two 

 portions of the boiler as to their evaporating power, as for example, 

 the superior conducting power of the thin brass of the tubes over that 

 of the iron plate of which the fire-box is made. 



In the 6th section an estimate is made of the loss of steam which 

 takes place by the safety-valves, during the work of locomotive engines ; 

 but it does not appear that there are any positive data on which to 

 found the assumption of the losses here assigned. The calculation is 

 based on the rising of the valve observed during the experiment com- 

 pared with the rise which is sufficient to give issue to all the steam 

 generated during the complete close of the regulator, without regard 

 to the pressure in the boiler, which must doubtless influence the loss 

 through the valve considerably. 



In the 7th section the quantity of water drawn into the cylinders in 

 the liquid state is shewn to amount to a considerable proijortion of 

 the water appended : the average of the severe experiments in the 

 table at page 289 is 24 per cent., and in one case it ajjpears to have 

 risen to 36 per cent. But as the determination of this quantity ne- 

 cessarily depends upon that of the loss of steam through the safety- 

 valves, it must be affected by whatever errors there may be in the 

 latter. We think it probable that the escape of steam through the 

 valve is more copious than M. de Pambour calculates it to be ; in 

 which case the loss hy priming would be found to be less considerable. 

 We are, however, compelled, in this instance also, to content ourselves 

 for the present with the data here furnished us. Besides, as we are 

 possessed of the facts ascertained by experiments, we must take it for 

 granted, that there is no great error in the total loss both by the safety- 

 valve and by pruning, as the only difficulty consisted in distributing it 

 between these two causes. 



The explanation of the manner in which a deficiency of steam-rooni 

 in a boiler causes it to prime is not applicable to a locomotive engine 

 for it does not follow, because that space is but 10 times the capacity 

 of the cylinder, that " at every stroke of the piston, a tenth of the 

 steam generated will pass into the cylinder," and that "the remaining 

 steam will be all at once reduced to 9-lllths of what it was before." 

 The truth is that there is no cessation either of the generation or sup- 

 ply of steam to the cylinders: the latter is at no instant more than 

 once and 4-lOths as rapid as at another, and is at the least nearly 

 8-lOths of the average supply. 



In chapter XI. the subject of Fuel is treated in a very scientific 

 and practical manner, both with reference to the absolute quantity 

 which locomotives of different constructions are capable of consuming, 

 and also with reference to the consumption required to effect a given 

 vaporization. 



From the experiments on this subject, of which the particulars are 

 given in the 1st section of this chapter, and which are grouped in a 

 table, page 298, according to the proportion between the heating sur- 



