IS^O.] 



THE CIVIL ENGINEICU AND ARCHITECTS JOURNAL. 



19 



whii'h all good engines built during flie l;ist 4 or 5 years liave been 

 able to overcome; tluit is, where the load was suflicientiv great, to 

 make the driving wheels revolve without causing the engine to ad- 

 vance. Strange as it may appear, no experiments have yet been made 

 to determine this all important point, and the "friction of iron on iron" 

 given in treati::es on mechanics, as equal to about ime-fuurth of the 

 weight, has been hitherto used in all calcii'ativiis as the maximum, 

 though numerous well authenticated pei/nrtnaiica: have shown, that 

 the ratio of the adhesion to the weight must have been nuich greater 

 than this. In a pamphlet written so late as year ISJ^S Messrs. Knight 

 and Latrobe, speaking of a performance of the Stonington locomotive, 

 which showed the adhesion to be equal to ^'jj; of the weight, sav " As 

 this is greater than we have known in any other case, it is presumed 

 that a portion of the weight of the tender was traid'erred to the engine, 

 &c. ; but performances of the engines of Baldwin and Norris on the 

 Philadelphia and Columbia railway, long before this pamphlet appear- 

 ed, go very far beyond this. 



In 183t), engines built by Mr. Norris, not exceeding 8 tons in weight, 

 drew loads equal to 400 tons on a level, which, if the weight on the 

 driving wheels was correctly given, showed the adhesion to exceed 

 one-third of the weight. Mr. Baldwin's engines have, however, since 

 exceeded even this, and have drawn loads equal to above 7i)() tons on 

 a level. Estimating the traction at 10 pounds perton, this will recpiire 

 a force of 700U pounds, and the weight on the driving wheels of Mr. 

 Baldwin's first class engines being stated at 12,ll!0 ])ounds, the adhe- 

 sion must have been equal to -^}j^ of the weight, if this did not ex- 

 ceed 12,120 lbs. or even adding 4000 pounds for the tender, equal to 

 n'^ of the insistent weiglit. 



After making every reasonable deduction, it appears beyond all 

 doubt, that the adhesion has been very much underrated, and, though 

 this alone keeps the power of locomotives within their present range, 

 I have never heard of a single direct experiment to determine this im- 

 portant law. In the edition of 183 1 of Wood on railroads the adhe- 

 sion is stated at one-twelfth, subsequently it is assumed by Mr. Knight 

 at one-eighth, or " half the friction of iron on iron," w liich value was 

 not determined by experiment but was merely deduced from the load ; 

 so again in the pamphlet already referred to, as late as last year, -^'^^ 

 is " greater than we have known in any other case." 



Since writing the above, I have seen the experiments of Mr. 

 Rennie on friction, as detailed in the 5th vol. of the Journal of the 

 Franklin Institute, 1830, and he there shows, that there is an increase in 

 the ratio with the increase of weight, the surfaces in contact remaining 

 he same. The extreme weights in 11 experiments, [p. 9,] are l"lj(5 

 cwt. and 5 cwt. per square inch, and with these pressures, the ratios 

 of the weights to the adhesion are respectively ;is 4 and 2-44 to 1. 

 The results of the experiments are very irregular, and though in this 

 particular case the ratio varies very nearly as the sipiare roots of the 

 weights, there is nothing to point out the law of increase, so as to 

 enable us to continue the table with any confidence. 



On the next page [10] it is stated that with ii'j cwt. Jier square 

 inch, cast and wrought iron abrade, and the friction is to the weight 

 as 1 to 2-3. Now, as the weight on the driving wheels is generalh' 

 2i tons on each, as the friction of wrought iron ou wrnuglit iron is 

 greater than on cast iron, as this difference is rendered the greatest 

 possible Vjy the parallelism of the fibres of the tire and rail, and as the 

 surfaces in contact can scarcely be one-fourth of a square inch, it is 

 evident, that tlie power required to produce motion, when the pres- 

 sure is 2i tons on a surface of much less than 1 inch s(piare, nuist 

 be more than ^'^^ of the insistent weight. It is stated, [p. 10,] that 

 hardened steel abraded with 10 tons per square inch, but the ratio of 

 the power to the weight is not given. 



The laws of friction, are however, only applicable as long as no 

 abrasion takes place, and this falls very far short of the case under con- 

 sideration, w here the pressure is often sutilcieut to cause even hardened 

 steel to abrade. Still these experiments and numerous performances 

 of the engines of Baldwin or Norris would lead to the conclusion, that 

 the adhesion is at least twice as great as that which Messrs. Knight 

 and Latrobe designate as "greater than we have known in any other 

 case." 



"The most interesting performances of locomotives which have 

 fallen under my observation are those detailed in the Franklin Journal 

 of June 1S3'.), wdiere an engine on S wheels, constructed by Messrs. 

 Eastvvick and Harrison, started, on a grade of .7 feet per mile, a load 

 of 2i)5 tons, subsequently overcoming with the same load, a rise of 35 

 feet per mile. This took place on the bad and crooked road between 

 Broad-street and the Schuylkill-bridge, where the traction must have 

 been 10 pounds per ton on a levo', and the entire force exerted by the 

 engine equal to 6000 pounds. In this engine there nre/utir driving 

 wheels, on wdiich the weight was 18,059 pounds, showing thus, that 

 the adhesion was equal to one-third of the weight even with the wkeli 



coupled. The weight on the driving wheels of Baldwin's eno-ines of 

 the first class, is one-third greater than on ««e pair of driving wheels 

 of the engines of Messrs. E. and H., and any sudden lurch of the engine 

 which, Willi the ordinary construction, will throw more than half its 

 entire weight on one wheel, will, with these engines, be distributed 

 on two wheels, and there can be little doubt, that an engine with the 

 usual weight on i driving wheels, will be more injurious than one with 

 twice that weight on f)ur drivers, as arranged 'bv iMessrs. R. and H. 

 Here is an engine which will with ease, draw 10;) tons n.'lt, up an 

 ascent of GO feet per mile, and which requires, on M.;// inclination, a 

 superstructure no more substantial than is required bv tlie lightest 

 engines of Baldwin or Norris, on roads varying from a'level to'20 or 

 30 feet per mile — and Una too witli aiitliracitc fiul. 



In the interesting pamphlets of Messrs. Knight and Latrobe, -already 

 referred to, those gentlemen state that the Camden and AndKiy Coiu- 

 pany " is now buildiiig, and have nearly completed, an engine' ujion S 

 wheels, and having two cylinders of IS inches diameter°by a 3 feet 

 stroke ; the wdiole supposed to weigh IS tons." **+'*" The 

 adhesion upon the rails of all the S wheels, is to be brought into action 

 by means of cog-wheels, &c." * * * * "This engine is designed 

 to lead burthen trains at moderate rates of speed ; but must be viewed 

 as yet in the light of an experiment." 



It is difficult to conceive howsucli, in other respects, keen observers 

 could pass by with cool indifierence the most striking fact related in 

 either of their interesting iiamphlets, and which, even without being 

 completely successful, would be attended with results infiuitelv more 

 important than the benefits resulting from all Americ;in improvements 

 in railroads and locomotives imited. In illustration, not explanation, 

 it may be proper to observe, that of all the engineers and machinists 

 with whom I have conversed for the last two or three years on this 

 subject, I have only found two engineers [the machinists would not 

 listen to it] who had given the subject that serious attention to which 

 it is, in my humble opinion, pre-eminently entitled. One of these 

 gentlemen, Mr. H. R. Cam])bell of Philadelphia, showed me, nearly 

 three years since an engine on S wheels and 4 drivers, which he was 

 then building to burn anthracite coal, and which certainly bore an 

 astonishing resemblance to the drawings of Messrs. Eastwick and 

 Harrison's engine in the Franklin Journal, and to the advantages of 

 which I have already alluded. 



We liave seen that with the 8 wheeled engine and 4 wheels coupled, 

 the adhesion was ecjual to one-third of the weight on the propelling 

 wheels, and if, with the 18 tons engme of Jlessrs. Stevens, we suppose 

 the adhesion equal to only one-fourth of the weight, we shall have a 

 machine capable of drawing lOOJ tons on a level, without greater in- 

 jury to the superstructure than the ordinary 8 or 9 tons engines of 

 Philadelphia, Baltimore, New York, Lowell," &c. An 8 wheeled en- 

 gine, weighing 10 tons, acting by the adhesion of its entire weight 

 distributed equally on the 8 w heels, will draw 9'J tons nett up an ascent 

 of liO feet per mile, and there will be no inducement to lessen this 

 weight, as it is on'y li tons per wheel, or the same as that on each 

 wheel of an ordinary freight or passenger car, w hen loaded. 



It is well known, that the ra])id destruction of wooden rails is not 

 caused so much by the natural decay of the timber conse((uent on its 

 exposed situation, as by the crushing under the driving wheels of the 

 locomotive, which destroys the lateral cohesion of the fibres of the 

 wood and admits water, the grand agent of decomposition. Notwith- 

 standing this disadvantage, the repairs of the wooden track of the 

 Utica and Schenectady railroad, do not exceed the repairs of the best 

 roads about Boston, (from 300 to 350 dollars per mile jier annum, the 

 renewal of the iron being neglected in both cases) and if an engine of 

 10 tons will not be more injurious to the superstructure, than an ordi- 

 nary car, it may yet appear, that this improvement alone, will reduce 

 the repairs and renewals of the common superstructure, below those 

 of the best road in the Union, omitting the assistance wdiich may rea- 

 sonably be expected from Kyan's, or some other mode of preserving 

 timber. 



It has frequently happened, that horse power has been used for a 

 short time after the opening of a road, by which the nice adjustment 

 of the rails as received from the hands of the engineers, has been little 

 if at all aU'ected. After the road has been travelled bv the engine, 

 however, even for a single week, with the very same cars, depressions 

 and inequalities will be found greater, as well as more numerous than 

 those which would be produced by the action of the cars only in sis 

 months or more. Timber as well as iron will bear a certain strain 

 without the least injury, but a slight increase beyond this, produces a 

 permanent set or deflection, hence, in reducing the weight from 

 2i to \\ tons per wheel, the relative strength of the superstructure is 

 not merely doubled, but is increased in a much greater ratio. This 

 proportion will be affected by the dimensions of iron and timber, kind 

 of wood, arrangement of parts, nature of earth, &c., but as a general 



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