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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



63 



strength from the rivet acting like a clamp. The (op is a plan of pillars 

 and cells ; the section is greater in the centre of the tube than at the ends 

 on accoant of the greater strain. Found a dilFerence iu the wrought iron 

 from different makers. Some irons stretch more than others, though the 

 ultimate strengths are about the saEne. Tlie ultimate strength of the iron 

 to resist tension averages 20 tons per square inch. A great deal depends 

 on the manufacture of iron ; some of the iron is very brittle, but its ulti- 

 . mate power to resist tensile strain is as great as more ductile metal. A 

 twelve-ton press laid on the top of the tube produced no deflection of the 

 iron, and a twelve-ton press fell on the top from a height of 25 feet, and 

 produced no other efl'ect than indenting the place where it fell. The loco- 

 motive does not run on the bottom cells, but the rails are on sleepers, sup- 

 ported by transverse plates G feet apart; the bottom is very rigid. When 

 the wedges were being taken out to let it lake its final bearing, the wedges 

 over a large portion of the centre had been left in by mistake, and it was 

 supported by the bottom being bulged up, which was a very severe test; it 

 did not belly up above 1 inch. The tube weighs 1250 tons without the end 

 caetings. When the tube was on its original platform, a straight line was 

 set out along the instrument with a thirlj-inch telescope, and holes drilled 

 through. The tube was constructed with a camber of 7 inches, that the 

 deflection might not be unsightly. The deflection is sensibly aftected by 

 changes of temperature. The motion caused by a cloud passing over the 

 •sun, or a shower, was quite visible by the means of an index. The whole 

 structure was a rectangular tube, 412 feet long, before it was moved to its 

 position ; it was floated to its position. When raised, C feet at each end 

 were added ; the bed for it to rest on was 3 inches of creosoted deal, a bed 

 plate 3 inches thick of cast iron, then another layer of creosoted deal to 

 prevent corrosion, a mass of red and white lead was spread over the tim- 

 ber , one end is thus a fixture ; the other is on a bed of iron, which rests on 

 44 rollers of cast iron, 6 inches diaineter, to allow of expansion and con- 

 traction. In addition to this, to prevent the sides being injured, the tube is 

 partly suspended by suspension rods riveted to the tube at each end, which 

 pass through girders bearing on metal balls, runuing in grooves ; it is cal- 

 culated that one-third is suspended, and two-thirds on the rollers. The 

 side of the tube is quite closed. The Conway and Britannia Bridges are 

 on similar principles; the Britannia Bridge has GO feet more span. The 

 Britannia Bridge is named after the Britaunia Rock in the Menai 

 Straits. There is one tube for each line of railway. The calculated deflec- 

 tion of the Conway Tube was about 7 inches, so the tube was cambered to 

 that amount. It actually deflected 7 j inches by its own weight. When 

 tested with 330 tons it deflected to lO^Jths inches below the original line ; 

 on removing the weight it returned to rather more than 8 inches. Proba- 

 bly some rivets had been disturbed. The effect of temperature was found 

 to be very great. The deflections taken at night di/Fered from those lakeu 

 iu the day time. The expansion of the cells at the top causes it to 

 rise. It is painted of a light colour to iucrease the radialiou. The 

 extremes of tempei-aturc cannot have an injurious effect, as the motion 

 is only 2 inches over 400 feet span. Iu raising the tube the strokes of 

 the hydraulic presses became isochronous, and the tube vibrated like a 

 shrinking plank, so that the presses had to be stopped. A train of 100 

 tons causes three-fourths of an inch deflection, but no vibration. Persons 

 in the carriages don't perceive that it is a tube. There is no increase of 

 deflection since it has been opened for traffic. The deflection is mea- 

 sured by an instrument attached to the side of the tube. There is 

 tremor when a train passes, but no vibration. It interferes with the read- 

 ing of a telescope. The tremor cannot be perceived by standing or 

 lying on the tube, it is greatest when a cannon is fired from the top. 



/. D. Marries Stirling, Esq. — Has studied the chemical properties of 

 iron. Ciist iron in this country consists of iron, carbon, silica, some phos- 

 phates, and other admixtures which may be considered impurities. Cast 

 iron from Sweden and magnetic ore is purer; it coutaius less carbon. The 

 strongest cast iron contains 3 per cent, of carbon ; a mixture of hot blast 

 No. 1 and cold blast No. 3 will give that proportion, but it would be 

 better for irou with that proportion to be produced at once from the blast 

 furnace. A small portion of arsenic increases the fluidity of iron. The 

 higher uumbers of hot blast irons apparently contain more carbon than 

 cold blast. Graphite is commonly to be seen on the surface of No. 1 hut 

 blast, not so frequently in cold. Chemical analysis gives vei-y little ditler- 

 ence between No. 1 hot blast and cold blast as regards the quantity of 

 carbon. It appears to be combined in a different manner; generally, 

 Scotch is the most, and Welch the least, carbonaceous iron; Staffordshire 

 is intermediate. Phosphorus gives the hot short quality to wrought iron. 

 Manganese closes the grain of iron ; apparently improves the quality ; gives 

 it a more steely character; increases the property of being hardened by 

 quenching. It does not give the elasticity of steel. Steel and cast iron 

 are improved by manganese. Berlin iron owes its fluidity to arsenic. 

 Dark iron is usually weak, grey usually strong, and white brittle ; black 

 iron wiien chilled becomes white, although it must be supposed to contain 

 the same quantity of carbon ; as a general rule, colour indicates treatment 

 to which iron has been subjected, and, in some cases only, the quantity of 

 carbou. Would employ colour as a test of strength, but uot of chemical 

 constitution. To resist a transverse strain, grey iron (not approaching to 

 mottled) would be best ; to resist a blow, grey iron, approaching to mot- 

 tled, would be best. The East Indian irou has many properties of malle- 

 able iron; its mixture with other pig-iron improves the quality of the 

 latter; small quantities are used in the patent boiler tube manufactory to 



improve the iron purchased for making wrought-iron. The best mixture 

 of iron for strength would be, for a large casting, a larger proportion of 

 No. 3 Scotch, Staffordshire, or Welch; fir a smill casting, a larger pro- 

 portion of Nos. 1 an 1 2, and a smaller of No. 3. Numbers of iron are, 

 however, very arbitrary : mixing iron adds very much to the strength. 

 Loudon founders improve their irons by the use of scrap iron. Ordnance 

 and hydraulic presses are made chiefly of No. 3; for a girder, more fluid 

 iron would be required. Iron cast iu large masses becomes soft from cool- 

 ing slowly. Has proposed to improve cast iron by an admixture of 

 wrought iron. There is a chemical combination between the two. The 

 quantity of carbon is diminished. Th.i grain is much closer. A small 

 quantity of wrought iron added to dark grey iron makes it light grey ; a 

 large quantity makes it mottled, a larger still almost white. Scotch iron 

 requires mo=t wrought iron, Staffordshire less, and Welch iron least. The 

 proportion for Scotch hot blast is for No. 1 from 21 to 40 lb. per cvvt. ; No. 

 2 from 20 to 30 lb. ; for No. 3 it is not recommended, as the iron is uncei-- 

 fain in itself. Staflordshire will not bear so much as Scotch ; 20 to 30 lb. 

 would be a high proportion for Staffordshire No. 1. Welch No. I bears 

 the same as Staffordshire ; No. 2 requires very much less. The increased 

 strength of the iron is aa advantage mechanically. From an average of 

 experiments tho waste in casting was 7 lb. per ton in favour of common 

 cast iron. The iron planes like wrought iron and the castings are more 

 difficult to trim than those of common iron. The first object in proposing 

 the iron was to raise the inferior irons to a level with the best, but has ob- 

 tuined a mixture stronger than the strongest. The improvement on strong 

 irons is not proportionably so much as on weak ones. It seems to bring 

 irons to an average. By adding wrought iron scrap to pig irou, and pud- 

 dling it, tlie resulting wrought iron is much improved. Cast iron easily 

 acquires magnetic power, and acquires extreme polarity without the power 

 of attracting small bodies to the degree that steel does. Considers it an 

 advantage that a beam of toughened cast iron need not be so heavy as that 

 of common iron. Has observed instances of alteration in the structure of 

 iron from repeated hammering, and shafts exposed to vibration also crys- 

 tallise. Considers that, possibly, galvanic action causes the change. 

 Cold hammering gun barrels too much makes them brittle. The mixture 

 of wrought iron with cast is made originally in the pig. The specific 

 gravity is from 7-2 to 7-3; the specific gravity of common iron from 69 to 

 7'3. The centre of a casting should be taken for the specific gravity. 

 Thinks it would be useful to inquire into the generic ditl'erences of irons. 

 Charles May, Esq, Ironfounder. — The difference in the strength of iron 

 appears to consist mainly iu the proportion of carbon. A large dose of 

 carbon makes a very tender iron ; the strength appears to be greatest 

 when the carbon is iu the smallest proportion that produces fluidity. The 

 greatest mixture of irons is preferred. One-third anthracite combined 

 with Scotch is a good mixture for toughness and strength. For small cast- 

 ings a more fluid iron is wanted than for large ones. On account of com- 

 petition, the cheapest iron is often preferred to the strongest. M'ith the 

 bulk of Scotch iron combines Welch and scrap iron ; the mixture is very 

 much reducible to the quantity of carbou. An iron very hard for small 

 castings would be soft from the slow cooling if run into a large mass. Cast 

 iron does not depend solely upon its constituent parts, but upon the bulk 

 into which it has to be run; these varying circumstances constitute the art 

 of the ironfounder in producing the greatest strength without any very 

 definite knowledge, either chemical or mechanical. By annealing, great 

 toughness can be produced [produced a shaving taken from the edge of an, 

 annealed cast iron wheel]. Hot blast iron ought to be as good as cold ; but, 

 in some cases, advantage has been taken of it to work up an inferior ma- 

 terial. Since the introduction of the hot blast the quantity of carbou com- 

 biued with iron is greater. Has not the same confidence for strength in 

 hot blast as iu cold blast iron. H.is met with hot blast iron as strong as 

 the strongest irou. The public would have no security in cold blast versus 

 hot blast irou. The fact of specifying for a particular quality of irou is 

 almost nugatory ; the principle of testing the work when done should be 

 adopted. Knows nocerlain mode of telling different kinds of iron; the 

 manner in vyhich cast iron is modified by the quantity of carbou it contains 

 is shown by chilling. The main feature as regards iron is a question of 

 the proportion of carbon. Considers Mr. Morries Stirling's mixture very 

 advantageous, particularly for irons too rich iu carbon. Would make tbe 

 breaking weight of a girder three times the greatest load. Considers that 

 railway girders are exposed to severe strains from the new foundations, 

 the violent impact they are subjected to, and the load being laid on and 

 removed suddenly. Would prove a girdei to once and a half or twice the 

 greatest load ; beyond that there is a chance of damage. Considers that 

 the side strain, from supporting the load on the bottom flange, would pre- 

 vent the girder bearing as much as if applied on the top. Thinks tests 

 should be applied as the weights are applied, in practice; but girders are 

 bought at the lowest possible price per ton, and ten times the profit would 

 not pay for experiments. Thinks the only limits to the length of simple 

 cast irou girders are practical ones, of handling large masses, and pouring 

 the metal equally to form good castings. If a large number of large 

 girders were wanted, it might be worth while to erect a new foundry for 

 the purpose. Is favourable to wrought iron girders. Considers that 

 wrought and cast irou may be combined so as to produce an advantageous 

 effect. When weight comes on the cast irou the wrought iron should take 

 its share of the load. Considers that, if well made, the joints and rivets 

 of railway bridges would not be injured by the vibration and impact to 



