176 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[ J t' K K , 



" It seems generallv agreed, that the bearing surface for the wheels to 

 run upon, without being too heavy, or so narrow as in an additional degree 

 to wear the wheels, should be about 2J inches ; and hence this Size of a 

 head is generally adopted for public railways. Although, both theoretically 

 and practically, it has been assumed, by Messrs. N. Wood, Barlow, and h. 

 Wood, that the strongest form of rail is that of which, with sufficient depth 

 for rigidity, the base does not contain too great a quantity of material,— and 

 though Mr. Barlow has given a formula for calculating the section of great- 

 est strength,— still the great object tliat the public are interested in, is the 

 best form of rail for safety ; and of which, while it has sufficient strength to 

 bear upon it heavy loads in motion, the bearers should not be too far apart, 

 to increase in the least degree the amount of either vertical or lateral deflec- 

 tion. When a rail possesses these advantages, its exact shape on mathenaa- 

 tical principles is of less importance than its convenience of being easily 

 fixed, and qnicklv shifted. Hence, while the single parallel rail is decreas- 

 ing in practical application, the double one, from its convenience, is progress- 

 ively extending. A knowledge of these facts is essentially necessary for 

 everv one engaged or connected with railways, whether he be a director or 

 shareholder, whether an engineer or manager. With all the knowledge yet 

 acquired, there is ample ,-vidence of tlie uncertainty which still hangs around 

 the subject ; and the great expense it has already cost some of the older 

 companies in making alterations, shows that experience to them has been 

 dearly boiii;lit. For example, it has been shown that the Liverpool and Man- 

 Chester Kailwav Companv has had several times to alter the rails on that 

 line ; to increase the weight from 35 lb., the weight of the original rail, to 

 50 lb., 65 lb., and 75 lb. per yard, successively; while the London and Bir- 

 mingham Railway Company, nntwithstanding the advantages derived from 

 Mr. Barlow's able report, was obliged to reduce the width of the bearings 

 or supports from 5 feet to 3 feet 9 incjies, and to increase the weight of the 

 rails from (A Ih. to 75 lb. On other railways equally expensive alterations 

 have been made. There is every probability, therefore, that, so long as that 

 plan of railway construction continues, whatever may be the first cost to 

 railwav companies, a still greater weight must be given to the rails, and a 

 still farther reduction of the width of the bearers must take place, in order 

 to adapt the stabilitv to increased rapidity of traction. 



" It mav he observed that the rails have gradually been increased in 

 strength since steam power was introduced! the bars are usually made in 

 12, 15, and 16 feet lengths, with square or butt ends, and are laid end to 

 end, the earlier complex contrivances to secure the joints being all dispensed 

 with, and the half-lap joints now rarely used. About j\ of an inch, at 

 least, should be left between the ends for expansion ; for it has been ascer- 

 tained that a bar of 15 feet in length will expand about ^\ of an mcli at 

 7^° F. Some have, indeed, proposed to place a small piece (t wood between 

 the ends of rails, as the difft-rent expanding properties of wood and iron 

 would fill the space, the wood expandmg as the iron contracts: but such a 

 plan is liable to ol.jection from tlie wood being likely to be shaken out, and 

 the space being left vacant. There is no part of railway construction that 

 requires more accuracy of fitting than the joints : the squareness of the ends, 

 and tlie space allowed for expansion, cannot be too carefully regulated. In- 

 stead of that, bow often are seen spaces at the joints of difTereut widths, 

 and the ends of the bars in juxtaposition, without paiallelism and uniformity 

 of level ; thus increasing llie amount of friction, adding to the joliiug and 

 rocking motion, and to the risk of the wheels of carriages being thrown off 

 the rails." 



This little work contains a large quantity of information in a very small 

 compass. The information is not perhaps quite profound or minute enough 

 to be of great value to the experienced engineer, but the student who is 

 commencing the subject will find here a general and compendious view of 

 it. which will form a useful and certainly a very interesting introduction to 

 more recondite researches. 



Railway Map of England and Wales.— Vlessrs. Arrowsmilh and Basire 

 have recently published the large railway map of England and Wales en- 

 graved by them for the Board of Trade from plans deposited there in 

 November last. Having only printed a few copies for the Committees of 

 the Houses of Lords and Commons, the publishers purchased the plates 

 from the Government, considering them interesting to the public, as giving 

 an authentic account of all railways up to the commencement of the present 

 time, showing those in oi>cratwn—\n progrcxs—iirojected—lUose tliat failed 

 at the Private Bill Office the end of December— and those for which peti- 

 tions were not presented to the House arterwards. 



A similar map of Scotland, and one of Ireland, are soon to appear. Of 

 the map before us we can give no better encomium than by saying, that its 

 magnificent size and the style of execution render it fully worthy of the 

 rei:u aliiin of the publishers, and of the occasion for which it was origin- 

 ally engraved. The size is 4 feet 9 inches by feet. 



OBSERVATIONS OX CAPILL.iEITY. 



By Prof. Henry. 



In 1830, the author presented the results of some experiments on tha 

 permeability of lead to mercury ; and subsequent observations had led him 

 to believe that the same properly was possessed by other metals in rcfe- 

 rence to each olher. His first attempt to verify this conjecture was mad« 

 with the assistance of Dr. Patterson, at the United Slates Mint. For Ihia 

 purpose, a small globule of gold was placed on a plate of sheet iron, and 

 submitted to the heat of an assaying furnace ; but the experiment was un- 

 successful; for, although the gold was heated much abovr its melting- 

 point, it exhibited no signs of sinking into the pores of the iron. The idea 

 afterwards suggested itself, that a difltreot result would have been ob- 

 tained had the two metals been made to adhere previous to heating, so 

 that no uxide could have been formed between the surfaces. In accordant* 

 with this view, Prof. Henry inquired of iMr. Cornelius, of Philadelphia, 

 if, in the course of experience in working silver-plated copper, in his ex- 

 tensive manufactory of lamps, he had ever observed the silver to disappear 

 from the copper when the nutal was heated. The answer was, that tha 

 silver always disap|iears when the plate is heated above a cerlain tempe- 

 rature, leaving a surface of copper exposed ; and that it was generally b«- 

 lie»ed by the workmen, that the silver evaporates at this temperature. 



Professor Henry ^-nggested that the silver, instead of evaporating, merely 

 sunk into the pores of the copper, and that by carefully removing the sur- 

 face of the latter by the action of an acid, the silver would reappear. Td 

 verify this by experiment, INlr. Cornrlins heated one end of a piece of thick 

 plated copper to nearly the melting-point of the metal; the silver at thu 

 end disappeared, and when the metal was cleaned by a solution of diluia 

 sulphuric acid, the end which had oeen healed presented a uniform sur- 

 face of copper, whilst ihe other end exhibited its proper coating of silver. 

 The unsilvered end of the plate was next placed, for a few minutes, in a 

 solution of muriate of zinc, by which the exterior surface of < opper wa» 

 removed, and the surface of silver was again exposed. This method of 

 recovering the silver before the process of plating silver by galvanism caii>a 

 iuti) use, would have been of much value to manufacturers of plated ware, 

 since it often hapiened that articles were spoiled, in the process of solder- 

 ing, by healing them to the degree at which silver disappears. 



It is well known to the jeweller, that articles of copper, plated with gold, 

 lose their brilliancy after a time, and that this can be restored by boiling 

 them in ammonia ; this elfect is probably produced by the ammonia acting 

 on the copper, and dissolving oti' its surface, so as to expose the gold, 

 which, by dilfusion has entered inio the copper. 



A slow diirusion of one metal thiough another probably takes place in 

 cases of alloys. Silver coins, after having lain long in the earth, bate 

 been found covered wiih a salt of copper. This may be explained by sup- 

 posing that the alloy of copper, at the surface of the coin, enters into coni- 

 binaiioo with the carbonic acid of the soil, and being thus removed, ill 

 place is supplied by a iliHusion from within ; and lu this way it is not iiu- 

 probable that a considerable portion of the alloy may be exhausleil in Iba 

 process of tune, and the purity of the coin be considerably increased. 



Perhaps, also, Ihe pi.eoomenon of what is called Sfgiegution, or the 

 formation of nodules of Bint in masses of carbonated lime, ami of indurated 

 marl in beds of clay, may be explained on the same principle. In break- 

 ing up these masse.-, it is almost always observed, that a piece of shell or 

 some extraneous matter occupies the middle, and probably formed tha 

 nucleus, around which the matter was accumulated by attracuuu. Tha 

 difficulty consists iu explaining how the attraction of cohesion, which be- 

 comes insensible at sensible distances, should produce this elTec. To ex- 

 plain this, let us suppose two substances uniformly dillused through eatk 

 olher by a slight mutual aitraction, as in the case of a lump of suj;ar dis- 

 solved 111 a large quantity of water, every particle of the water will attract 

 to Itself its proportion of the sugar, and the whole will be in a state of 

 equilibrium. It the diBusion at its commencement had beeu as.-isted by 

 heat, and this cause of the separation of the homogeneous particles no 

 longer existed, Ihe dillusiou might be one of unstable equilibrium ; and the 

 sliglilest exir.ineous force, such a.i the atiraction of a minute piece of shell, 

 might serve to disturb the quiescence, and draw to itself the dillused pai- 

 tules which were immediately contiguous to it. This would leave a ve- 

 cuum of the atoms around the alliacling mass : for example, as in the case 

 of the sugar, there would be a porliou of the water aiouul the nucleus de- 

 prived of the sugar; this poilioii of the water would attract its portion of 

 sugar from the laver without, and into this layer the sugar from the layer 

 next without would be dillused, and so on until, through all the water, tba 

 reiimiMiiig sugar would he uniformly dillused. The process would COD- 

 liuue to be repeated, b> the nucleus agaiu attracting a portion of the sugar 

 from the water ininiediately around ii, and so on until a considerable uc- 

 cuinulaliou would be lornieU around the foreign substance. 



Wf can iu this way conceive of the manner by which the inolecular 

 aclion, which is insensible at perceptible distances, may produce resulu 

 which would appear to he ihe elft-i t of attraction acting at a distance.— 

 From llie Pruc. of the American Philosophical Society. 



