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THE CIVIL ENGINEER AND ARCHITECrS JOURNAL. 



[^Februakv 



Some engines weigh nearly 30 tons ; a new one on four wlieels weighs 32 

 tons. Has observed that the internal structure of small pieces of wrought 

 iron becomes altereil by blo^vs. Caused a piece of the best and most 

 fibrous wrought iron from the Lowmoor works to be hammered by black- 

 smiths for 10 minutes, and quite a change in the texture was produced ; 

 by continuing the hammering for lialf-ao-hour, it was altered from a 

 fibrous to a granular texture. Axles are not exposed to the same sort of 

 blows as hammering gives; but axles have broken with a crystalline 

 fracture. The very heavy engines lately introduced begin to crush the 

 rails ; eight tons on each wheel seems beyond what the rails as now con- 

 structed can carry. The wheels of the large engine above mentioned are 

 16 feet apart. It has travelled with two carriages at 78 miles per hour. 



Robert Slephemoii. Etq., M.P., Civil Engineer. — Mentions that it is well 

 known that the fluidity of Berlin iron is due to the presence of arsenic, and 

 that the M'elch and Yorkshire irons are contrasted by (he one being hot- 

 short and the other cold-short, which is due to the presence of phosphorus 

 on the one hand and manganese on the other. Used two or three cwt. of 

 the new iron from India; but tiie workmen did not understand it; it 

 retains its malleable properties to a high temperature, and then loses them 

 very suddenly and becomes fluid. Mr. Worries Stirling's method of intro- 

 ducing wrought iron into cast iron, is a commercial question, unless it 

 gives more flexibility or toughness to the cast iron and makes it approach 

 the quality of wrought iron ; for if the additional quantity of common iron 

 required to make up for the difference of strength can be introduced at less 

 expense than his mixture can be procured, he would be beat out of the 

 market. Weight is, however, an important element in steamboats. Pre- 

 fers a mixture of irons wherever it can be obtained, without having any 

 specific opinion as to which mixture is best. iMade several experiments 

 on mixtures at Newcastle ; does not think the difference between any irons 

 30 great as to make it worth while incurring additional expense ; 5, 6, or 7 

 per cent, is probably the range on one side or the other from the medium 

 of all (he irons in this country ; wlien using hot blast iron, alters the con- 

 stant in Mr. Hodgkinson's formula (o make up for any defect in quality. 

 Hot blast iron being very fluid, is better adapted for small articles than 

 cold blast ; it appears to approach the Berlin metal. Would use either 

 hot blast or cold blast iron, but prefers a mixture. Though you may 

 specify that the iron be without cinder, you cannot ensure getting it. Has 

 not found much difference between anthracite and o(her iron. The large 

 castings for the bridge at Newcastle are of anthracite and hot blast from 

 the neighbourhood. Considers that there is very little ditference between 

 the strengths of different irons, and tliat it can always be made up by 

 varying the constant in the formula. Never met with iron varying 15 per 

 cent, from a standard. Is of opinion that, taking the average of irons in 

 this country, there is a great proximity to an uniform standard ; irons vary 

 to a small extent on each side of that standard. Though one iron com- 

 pared with another may give a great difference of strength, a mixture, for 

 which all engineers stipulate, annihilates these variations. Always adopts 

 Mr. Hodgkinson's formula. Adopts the constant he gives, viz. 23 or 26 

 with a mixture; if compelled to use hot blast iron, would take 20 as the 

 constant, this number being d erived from experiments. Has not the same 

 confidence in hot blast as in cold blast iron, rather from opinion than 

 experiments. Understands that the fracture of hot blast is darker and 

 more carbonaceous than cold blast, which should be a dull lead grey. 

 Generally employs six times the working load to be the calculated 

 strength of a girder, and tests it with a wsight equal to two trains of loco- 

 motives, or two tons per foot in length. Has added to the bridges built 

 on the plan of the Dee Bridge, three castings corresponding to the lower 

 ones, by means of which the line of thrust is raised above the horizontal 

 line. 'The deflection of abridge of 96 feet span so altered was l'9G inches 

 with 56 tons in the centre, equal to two [rains of locomotives; it is rather 

 too stiff; considers that a certain amount of flexibility in a cast iron girder 

 is essential to resist the suddenness of the passing weight ; it should yield 

 so as not to convert pressure into concussion. Tests large compound gir- 

 ders to one-third the breaking weiglit, and small simple girders to one- 

 sixth. Tests small girders with the hydraulic press ; large girders, with 

 dead weight, suspended from the centre. Iron clamps holding the boltom 

 flange support the platform for the testing weight. The weight is applied 

 in the centre. In bridges it is applied on one side, but the torsion so 

 created is very inconsiderable and may be disregarded. It is nut neces- 

 sary to lest girders with weights applied as in practice; the b.-ams tliat 

 form the platform rest close to the vertical web. When girders have been 

 tested accidentally in that way, has not found any difference; svhen two 

 girders are tried by the hydraulic press it is by accident only tliat the pres- 

 sure is exactly in the verticil plane. Does net consider that alierations 

 take place in iron bridges from length of time or change of lemperature ; 

 the engine beam of a Cornish engine, willi a 90 incli c>liiider, receives a 

 shock 8 or 10 times a minute, equal to .55 tons ; has known them work far 

 20 years without the smallest perceptible change. On the Blackwall 

 Railway, 120,000 trains, each of 12 carriages, have passed over girders of 

 48 or 50 feet span, and when examined four or Ave months ago, no percep- 

 tible change had taken place. These girders were not made to carry 

 locomotives, and they are doing as near their ultimate duly as girders 

 carrying locomotives. With respect to the question of change in the internal 

 structure of wrought iron, knows of no instance where some important 

 link was not wanting to complete the reasoning; tliat hamnieiiug may 

 produce britlleness iu iron is probable but not certain ; the couueciing rod 



of a steam engine vibrates at ordinary speeds eight times in a second ; one 

 just come into the shop from the Norfolk line has run 50,000 miles ; the 

 rod has vibrated 25,000,000 of times ; yet, apparently, no change can be 

 detected. With respect to axles, has never been able to come to a con- 

 clusion whether the axles that broke were fibrous to begin with. The 

 connecting rod being so much smaller, is more likely to be fibrous ; a piece 

 of iron rolled from 1 foot to 20 feet is almost necessarily fibrous ; but 

 when rolled from 1 foot to 6 feet it is not necessarily so. Does not believe 

 any change takes place in cast iron. Considers ^rj th of an inch to afoot 

 may be allowed as the deflection for a girder. Considers the deflection 

 from a moving train to be less than that from one at rest. There may be a 

 lateral strain, but is satisfied that the vertical strain is less. Adopts Mr, 

 Hodgkinson's firm of girder, with slight variations according to circum- 

 stances. Usually puis two girders under one rail with a baulk of timber 

 between for short spans ; in some cases it is desirable to have no top flange. 

 With statical pressure adopts 3 to 5 as the proportion of the top to tlie bottom 

 flange. The difficulties of casting prevent the theoretical proportion being 

 always the best. In large girders has sometimes adopted Mr. Hodgkinson's 

 proportion of five to one. In some cases has made the top and bottom 

 flange equal; although some part of the metal may be thrown away as far 

 as strengih is concerned, it is very useful for other purposes. Has made 

 cast iron girders 50 feet long, but now limits them to 40 feet, and then 

 uses wrought iron. Kor small spans almost invariably uses two girders, 

 with a baulk of wood between, under each rail; it is a convenient way of 

 disposing of the material and getting sound castings, and they are easily 

 handled. They are being used at Penmaen Mawr, where there were 19 

 spans of 35 feet each. The timber forms a cushion for the rail. In bridges 

 beyond the limits of cast iron girders considers that girders formed of 

 separate castings, with a tension rod along the bottom is as good a form as 

 any ; but considers that there is this advantage in having the tension rods 

 at an angle, that you can bring the tension of the wrought iron into play 

 so easily. When such a bridge is wanted on a large scale, the vertical 

 elevation might be divided. When the joints are planed and fitted accu- 

 rately, such a girder would be as secure as a solid one, as in a large mass 

 the contraction from cooling is liable to be unequal. Has tested compound 

 girders without auy bolts and depending on the tension bar, and also with- 

 out the tension bar but depending on the bolts. The extension of tension 

 bars with 10 tons per square inch is ^^^th of the length, and the iron 

 comes back to its original state. The piston rods of Cornish engines go OQ 

 without being lengthened. Tension rods will not permanently suffer as 

 long as the strain is within the limits of elasticity. With respect to the 

 tension rods in the Dee Bridge which acted at an angle, does not allow the 

 objection that with deflection they might become slackened, but would 

 undertake to break the tension bars by putting on a strain, and that the 

 girders can be cambered by them. Would use wrought iron girders over 

 spans where there was no limit as to expense or levels. Thinks that a bar 

 of wrought iron cast into the bottom flange of a cast iron girder might be 

 too intimate an union on account of the different rates of expansion of the 

 metals; if, however, the proportion of cast iron to wrought was very large, 

 it would not be of so much consequence. It is much the same as bolting 

 a wrouglit iron bar to the boltom flange of a girder. Does not consider 

 that the vibration and impact to which railway bridges are subject would 

 injure the bolts and rivets. Has observed one or two instances when 

 oscillation was produced on skew bridges wheu the road has not been in 

 good order close to the bridge, and one wheel came on to a solid angle 

 when the other was on soft ballast; generally now brings the two sides 

 square by means of a wooden baulk, la skew bridges, when oscillation 

 is prevented, both girders are subject to the same vibration. The deflec- 

 tion of a girder would not throw the engine into oscillation; the engine 

 moves at the rate of about 70 feet per second, and there is not time. The 

 deflection of the girder is only a small objection. The approach to the 

 bridge causes the danger. Considers experiments on impact and vibratioa 

 advisable. An ordinary train weighs about five eighths of a ton per foot 

 in lengtli. Engines are about a ton to a foot in length. Considers wrought 

 iron girders preferable to cast iron for spans exceeding 40 feet, as being 

 more elastic. Found a very marked eft'ect from introducing a cast iron 

 top in the box girder in the Chalk Farm Bridge. Considers a collection of 

 facts would be very valuable, but any legislative enactment, with refer- 

 ence to the construction of bridges which would hamper engineers, would 

 be very objectionable. Attaches very little importance to vibration, and 

 considers it of little consequence for girders to be laid on ordinary walls 

 without inlerposing medium. Considers suspension bridges very little 

 applicable to railvvays ; indeed, with the prospect of increasing weights, 

 to;ally inapplicaljle. Thinks Dredge's principle scarcely applicable with 

 heavy weights. The more ties they have to the platform the better. Has 

 been informed that a train passing over a suspension bridge at Stockton of 

 300 feet span caused a wave 2 feet high like a carpet. Understands that 

 American engim-ers have given up lattice bridges entirely ; they soon rack 

 themsi-lves to pieces; the timber is cut into slices instead of being in lumps. 

 The thin bars of an iron lattice bridge make it impossible to convey com- 

 pression through them ; it is " wabbly." Sir John M'Neill has remedied 

 ihe want of power to resist compression by putting a cast iron top. Es- 

 liibiti-d drawings of (he wrought iron girder for the Chalk Farm Bridge, 

 with a CHSt iron top to resist compression. The method adopted to 

 strengthen girders on the Dee Bridge plan, and girders with tension rods 

 along the bottom flange for bridges over the Kiver Arno. Also an expert- 



