As 650 volts is allowed by the Board of Trade as the maximum pressure at generating-stations and on feeders, he suggests that the pressure on the overhead trolly-wires should be raised by the Board of Trade from 550 to 600 volts. This would reduce considerably the cost of feeders and also the present heavy currents dealt with on tramway systems. In the bonding of feeder-pillars and poles to the rails, the bonds should be kept as far away as possible from pipes or metallic structures. If gas-lamps are attached to tramway-poles, at least triple insulation should be provided from the trolly-wires to the span wires and poles, and the poles should be unbonded. All rail-joints should be properly bonded and tested periodically, and where there are welded joints a copper bond is recommended across each weld. Welded joints have been greatly improved in recent years, so as to avoid as far as possible gas cavities or inclusions of oxide or slag. It is therefore to be hoped that honeycombed joints exist no longer. The Author desires to express his indebtedness to Mr. L. Aitchison, M. Met., for valuable advice and information relating to the chemistry of corrosion. His best thanks are due also to Mr. L. S. M. Marsh, M. Inst. C.E., for the loan of pipes, from which photographs were taken, and for analyses of the same; and to Mr. J. W. Morrison, M. Inst. C.E., for allowing a survey to be made of gas-mains, and their positions located with reference to the Sheffield tramway-track. The Paper is accompanied by two drawings, from which the Figures in the text have been prepared, by two photographs, and by the following bibliographical Appendix. [BIBLIOGRAPHY. BIBLIOGRAPHY. 1898. H. F. PARSHALL: "Earth Returns for Electric Tramways." Journal of the Institution of Electrical Engineers, vol. 27, p. 440. 1901. W. WARK: "The Use and Durability of Wrought-Iron Pipes." Minutes of Proceedings Inst. C. E., vol. cxliii, p. 259. 1902. S. KROHN: "Ueber Messungen der elektrischen Ströme in den städt- W. R. COOPER: "The Present Position of Electric Traction on Tramways 1903. W. R. WHITNEY: "Corrosion of Iron." Journal of the American Chemical Society, vol. 25, p. 394. C. HOPKINSON, B. HOPKINSON and E. TALBOT: "Electric Tramways.” J. T. MILTON and W. J. LARKE: "The Decay of Metals." Minutes of 1907. A. P. TROTTER : Remarks on Electrolysis in the Discussion on "SinglePhase Electric Traction." Minutes of Proceedings Inst. C.E., vol. clxvii, p. 74. W. H. WALKER, A. M. CEDERHOLM and L. N. BENT: "Corrosion of Iron A. S. CUSHMAN: "Corrosion of Iron." Bulletin No. 30 of the United Journal of the 1909. J. G. and R. G. CUNLIFFE. "Electric Traction Vagabond Currents." Journal of the Institution of Electrical Engineers, vol. 43, p. 449. 1911. C. F. JENKIN Remarks on Difference of Potential in Alternating-Current Circuits, in the Discussion on "The Electrification of a Portion of the Suburban System of the London, Brighton and South Coast Railway." Minutes of Proceedings Inst. C.E., vol. clxxxvi, p. 67. 1913. J. G. and R. G. CUNLIFFE: "Some Problems in Traction Development— Tramway Feeding Networks." Journal of the Institution of Electrical Engineers, vol. 50, p. 692. 1914. E. H. SCOFIELD and L. A. STENGER: "Corrosion of Metals in Natura Soils." Electric Railway Journal (New York), vol. xliv, p. 1,092. Technological Papers of the Bureau of Standards, Washington, No. 32. Discussion. The PRESIDENT moved a vote of thanks to the Author for his The President. Paper. Mr. HARRY E. JONES wished, on behalf of those members of The Mr. Jones. Institution who had suffered most loss and trouble in connection with the subject, to acknowledge the frank, impartial, and dispassionate tone of the communication, and to thank the Author for a certain amount of light he had given to those engineers who were not chemists or electricians, and yet who were able to follow the arguments in his Paper. The destruction noticed in underground pipes had been very much reduced in England, especially in London, by the introduction of the more recent Board-ofTrade rules. Having considerable knowledge of very large systems in London, he could say that, in spite of the almost universal adoption of electric traction on tramways, there was practically very little loss or injury now being occasioned. It was rather different abroad. He had placed on the table some specimens of pipes brought recently from Bombay, where through known leakages of current very serious and rapid injury had been done. The pipes became defective and leaky within a few months, whereas their ordinary life should have been about 15 or 16 years. There was reason to believe that the introduction of mild steel, now used extensively for pipes, had something to do with the matter. There had been recent discussions in the Institution on the corrosion of steel piles in salt water, and on corrugation in tramway-rails, and he thought the discussion pointed to there being some inherent defect in the constitution of the cheaper and rougher forms of steel, which perhaps were not sufficiently homogeneous in structure. Personally he had gained much information from the Author's suggestion that apart from direct leakage of electric current electrolysis might be set up by chemical reactions of the different components in a material which incorporated several different metals that were not completely mixed. He had had some very unsatisfactory experiences in England in connection with the plating of gasholders. The cheapness and ductility of mild steel, and its freedom from cracks due to riveting, had led [THE INST. C.E. VOL. CC.] G Mr. Jones. him to adopt steel extensively of late years in the construction of gasholders, and he knew of two instances abroad, one in Bombay and the other in Calcutta, and two instances in England, where comparatively modern structures had been affected in a manner which was quite foreign to previous experience. Instead of the metal becoming exfoliated by ordinary rust and corrosion, it was penetrated in a way which almost suggested the use of a drill. In a gasholder at Eastbourne which had been causing much trouble and anxiety for some time there were certain plates, out of thousands of square feet of plating, without a single penetration, while others had a single hole in them like a hole in wood eaten away by the teredo. In the gasholder at Eastbourne after about 20 years, in another at Faversham after about 12 years, in one at Calcutta after 6 or 7 years, and in another at Bombay after about 12 years, the leakage was so serious that very extensive repairs had to be taken in hand. In several of the cases there could be no direct connection with stray electric currents, unless they were in the air. All four gasholders were exposed to the influence of sea-scud which might bring chlorine into the atmosphere, but he had been led by the Author to look for the presence of carbonic acid in damp air. It was rather curious that although the holders in question were subject to the action of sea-water in minute particles brought by the storm winds, the worst penetrations were not on the windward or seaward side, but on the side opposite the chimneys connected with the Siemens furnace used for heating the retorts. The presence of such minute penetrations at considerable distances apart, and in some cases in dozens of plates, gave him the impression that there must be something at fault in the constitution of the steel itself; possibly, owing to the metals not being thoroughly mixed in the plates, anodes and cathodes were formed which gave rise to galvanic action. He rather concurred with the Author that all rusting of iron was due to galvanic disturbance set up in that way. The Paper opened a new field of investigation, and as soon as the gasholder could be spared he intended to send some of the plates to the National Physical Laboratory with a view to the condition of the steel being thoroughly examined, in order to find out what should be avoided. In Bombay recently he reconstructed a gasholder and put in a very large proportion of new iron plates. to replace the steel plates found to be insufficient. Sir John Snell had been advising them in Bombay on the question. Although the destruction had been attributed to stray currents, there was a certain amount of destruction which could only be attributed to local galvanic disturbances, to which the Paper pointed. Mr. A. P. TROTTER remarked that the subject was one upon Mr. Trotter. which he had spoken at considerable length in the Institution,1 and to which he had given very close attention for the last 18 years. Some engineers did not quite recognize the position in which the tramway industry was placed with regard to electrolysis. In 1893 Lord Cross's Committee reported that danger from electrolytic action appeared to them to have arisen from a faulty system of constructing electric tramways, and were of opinion that it could "be reduced by improved methods of construction so as to be practically negligible." They ordered protective clauses to be inserted in electric traction Bills and Provisional Orders. The effect of these was that if the undertakers adopted and employed reasonable and proper precautions, and such other means as the Board of Trade might direct, having regard to the expense involved and to the effect thereof upon the commercial prospects of the undertaking, the undertakers would be indemnified against any electrolytic damage which they might do. Engineers had sometimes grumbled at the regulations, not realizing this indemnity; but tramway men generally had recognized that the whole responsibility was removed from them and was taken by the Board of Trade, and they had considered that this was worth the expense involved. But this comfortable state of affairs had led to a somewhat unfortunate apathy about the matter, and only very few engineers, such as Mr. H. M. Sayers and Messrs. J. G. and R. G. Cunliffe, had given attention to it. The responsibility which Sir Courtenay Boyle took up on behalf of the Board of Trade in 1893 was a serious one. He could do it, for he had a good grasp of the subject. If it could be proved in any case that electrolysis had taken place where the regulations had been complied with, the blame would rest with the Board of Trade for the inadequacy of their regulations, and would devolve on the officer who originally drafted, or the one who was responsible at the time, for the periodical revision of the code. Twentyone years had passed since the regulations were first issued, and no case had been proved. It had been suggested that this pointed to the conclusion that the rules were too strict, for Lord Cross's Committee only hoped that danger would be reduced " so as to be practically negligible." It might appear that an indefinitely great factor of safety had been adopted. But the margin was not unknown. Certain of the regulations could not be relaxed without risk. It was true that some of the original regulations could not be sup 2 Minutes of Proceedings Inst. C.E., vol. cli, p. 93, and vol. clxvii, p. 73. |