Minutes of Proceedings of the Institution of Civil Engineers

joints as the girder plating; but this was not the case. In the shell plating the tension was due to pressure acting on a curved surface; and it acted with the same pressure on the weak joint as it did on the strong plate. When the tension became greater than the strength of an unassisted joint, the joint began to bulge; in other words, it assumed a curve of less radius, by which it was still able to resist the pressure; but as the pressure increased so did the bulging, until the rivets were sheared or the plate torn through the rivet-holes. This occurred long before the solid plates, with which it is assisted on both sides, attained their ultimate resistance.

The following experiments were made to ascertain the strength of circular furnaces as usually constructed for marine boilers: two furnaces, 3 feet in diameter and 6 feet long, were built up in two lengths, one 4 feet long and one 2 feet long. Each length was made of one Lowmoor plate, the ends being connected by a single riveted joint, so arranged as to admit of a true circle being kept. The ends of the tubes were flanged, and connected by rivets to each other, and to a strong boiler shell in the usual way.

They were subjected to water pressure until the weakest tube collapsed, when, after it had been shored up, the experiment was continued until the following results were obtained :—

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From this it would be seen that the Board of Trade rules for circular furnaces agreed as closely as could be expected with the experiments, and that their factor was 6 for water pressure; but when the crowns of the furnaces were partially covered with even a thin scale, and exposed to the action of a strong fire, the factor 6 would probably be reduced to a factor 4.

It would be seen that the 4 feet lengths were only from 10 to 15 per cent. weaker than the 2 feet lengths, yet he would strongly advise the use of strengthening rings, provided they were so constructed as not to encourage deposit. He had seen the crowns of overheated furnaces brought down to such an extent that had not

the strengthening rings retained their shape, fatal explosions must have taken place. The Board of Trade rules for boilers were inconsistent in many respects, and must be revised before they could command confidence. Their strongest boilers have factors of 6, and the weakest boilers had factors of 4.

If their weakest boilers were safe, their strongest boilers involved a waste of materials. He did not wish to raise a doubt on the strength of their weakest boilers, as such boilers only furnished additional proofs that an actual factor of 4 was a safe factor. Take a boiler containing 18 lbs. of water for each square foot of heating surface, and let steam be raised to 60 lbs. pressure. With good fires and no escape for the steam, in about seven minutes the pressure would be doubled, and in about nine more minutes the pressure would be quadrupled; but if the boiler contained only 9 lbs. of water per square foot of heating surface, the same pressures would be generated in about three and a half and four and a half minutes. Such a case could not be met by increased strength of boiler, but over pressure could be prevented by keeping the safetyvalves in good working order. The Board of Trade would not pass any safety-valves unless they were capable of discharging all the steam the boilers could be forced to generate at a pressure not greater than 10 per cent. above the working pressure, for which they deserved the best thanks of the public. The weakening action due to unequal expansion, and also by overheating, cannot be overcome by increased thickness of the plates. Unequal expansion could be prevented by increased circulation when getting up steam; and overheating could be prevented by keeping the boilers clean and the water at its proper level. Against the weakening action of corrosion, extra material must be provided for some parts to a very slight extent, as for instance the horizontal seams of rivets in the cylindrical shell; and for other parts to a greater extent, as for instance the stays; but to what extent such extra material was provided, was as much a matter of durability as it was a matter of safety,

• For new boilers the Board of Trade rules allowed a working strain of 5,000 lbs. per square inch of net stay area, the factor of safety being 10. A screwed stay 11 inch in diameter over the threads, was 11 inch in diameter at the bottom of the threads; and when reduced by corrosion to 13 inch in diameter it would have a factor of 6. If then inch was a sufficient addition to the 13 inch stay, surely inch should also be a sufficient addition to a 1 inch stay; but the Board of Trade rules assumed that, in a given time the reduction by corrosion would be in direct propor

tion to the diameter of the stay and to the thickness of the plate, which was inconsistent with experience.

November 20 and 27, 1877.

GEORGE ROBERT STEPHENSON, President,
in the Chair.

The discussion upon Mr. HoLT's Paper, "On the Progress of Steam Shipping," occupied both these evenings.

December 4, 1877.

GEORGE ROBERT STEPHENSON, President,

in the Chair.

THE following Candidates were balloted for and duly elected :WILLIAM FOX, JAMES NINIAN HILL, DAVID FRANCIS HOGARTH, JOHN GALE JOPP, THOMAS COLTIM KEEFER, JOHN HENRY LOWE, ALAN MACDOUGALL, WILLIAM MORTON, WILLIAM COLTON PARKER, WILLIAM FURNISS POTTER, and LOUIS SCHWENDLER, as Members; LAWFORD MACLEAN ACLAND, Stud. Inst. C.E., WILLIAM RICHARD ACTON, AMBROSE AWDRY, Lieut. R.E., ALFRED BACHE, B.A., ROBERT THOMAS OLLIVIER BARBENSON, MARTIN BLOXSOM, EDWARD HENRY BOLD, ROBERT WILLIAM BOURNE, JAMES EDWARD NEVILLE BOYDELL, GEORGE JAMES COTTOM BROOM, GEORGE VAUGHAN BROWN, Stud. Inst. C.E., THOMAS COMMON BROWN, ADOLFO GARCIA CABEZAS, ALFRED EDWARD CAREY, Stud. Inst. C.E., JOHN CARLINE, CHARLES FREDERIC CLOUGH, HENRY JAMES COLES, CORNELIUS CORNES, JAMES CROFTON, Col. R.E., MATTHEW CURRY, Jun., Stud. Inst. C.E., CHARLES EUGENE DE RANCE, FEDERICO EDUARDO DUBOC, Stud. Inst. C.E., HENRY EVAN GRIFFITH EVANS, Stud. Inst. C.E., HENRY SOMERSON FREEMAN, THOMAS LINDSAY GALLOWAY, JUSTINIANO AURELIO GALVEZ, Stud. Inst. C.E., ARTHUR CHARLES GOTTO, Stud. Inst. C.E., JOHN PURSER GRIFFITH, JOHN GREEN HALL, FREDERICK GEORGE HANKIN, Col. M.S.C., HENRY GRAHAM HARRIS, ALFRED HOPKINSON, JOHN HOPKINSON, M.A., D.Sc., HENRY HOWARD, ROBERT HIGGS INCH, ALFRED JOHN INGRAM, Stud. Inst. C.E., JAMES IRVINE, GEORGE JESSOP, Stud. Inst. C.E., WARWICK HUSON JOHNSON, THOMAS ISAAC LILLEY, FRANCIS GASCOIGNE LYNDE, DAVID MANUEL, HENRY ROBERT HOWELLS MARTIN, Stud. Inst. C.E., WILLIAM JOSHUA MASON, Stud. Inst. C.E., HENRY MERRYWEATHER, LEANDER MUNRO MILLER, BOSWELL PARKINSON MILSOM, Stud. Inst. C.E., OCTAVIO

OLAVEGOYA, Stud. Inst. C.E., Alfred Perry, WALTER PITT, CLEOPHAS WILLIAM RATLIFF, CHARLES LAWRENCE PEMBERTON ROBINSON, B.A., Stud. Inst. C.E., RALPH SADLER, Stud. Inst. C.E., CECIL SCOTT, Stud. Inst. C.E., ARTHUR EDMUND SHAW, JOHN WALLIS SHORES, Stud. Inst. C.E., GUY SMITH, JOHN MOTLEY SMITH, HENRY FRANCIS SNEYD-KYNNERSLEY, ROBINSON SOUTTAR, HENRY LEWIS SPINDLER, FREDERICK STAFFORD, ALEXANDER STARK, Stud. Inst. C.E., GEORGE ERNEST STEVENSON, GEORGE WILLIAM SUTCLIFFE, JAMES TAIT, Stud. Inst. C.E., WILLIAM UPTON TINNEY, THOMAS WILLIAM MATTHEWS TISDALE, WILLIAM BLOMEFIELD TRIPP, GEORGE EDWARD VINT, Stud. Inst. C.E., JAMES WILLIAM WARDLE, Stud. Inst. C.E., WILLIAM HENRY WARREN, CHARLES HENRY BILLINGHURST WHITWORTH, Stud. Inst. C.E., and WILLIAM BOOTH WOODHEAD, as Associates.

It was announced that the Council, acting under the provisions of Sect. III., Cl. 8, of the Bye-Laws, had transferred JOHN HENRY ABBEY, THOMAS AVELING, ROBERT BALLARD, JOHN BARKER, HENRY BESSEMER, THOMAS CARGILL, JABEZ CHURCH, JOHN DONALDSON, JAMES HENDERSON, JOHN WILLIAM INGLIS, HENRY JOLL, CHARLES FERDINAND DE KIERZKOWSKI, GEORGE KILGOUR, JAMES HENRY LYNDE, EDWIN MUIR, ROBERT CARSTAIRS REID, ARTHUR LEWIS STRIDE, JOHN ISAAC THORNYCROFT, and JOHN EVELYN WILLIAMS, from the class of Associate to that of Member.

Also that, under the provisions of Sect. IV. of the Bye-Laws, the following Candidates, having been duly recommended, had been admitted as Students of the Institution:-THOMAS VICTOR BAMFORD, BERNULF WATSON BEEVER, AUGUSTUS WILLIAM HARVEY BELLINGHAM, FREDERICK BENJAMIN BROWN, WALTER ASPINALL CARVER, CHARLES JOHN CORRIE, ALFRED CORRY, WILLIAM ALGERNON DARLING, HENRY BONIFACE DAVIS, SYDNEY FIRTH, AUGUSTINE SEATON GEORGE, JOSEPH GREENWOOD, SYDNEY JOHN JAMES HACK, CLEMENT HILL, JOHN EDWARD JONES, THOMAS NESHAM KIRKHAM, Jun., JOHN ALEXANDER MCDONALD, ARTHUR WOODBYNE PARISH, SEPTIMUS PENNY, ARTHUR PINE, LANCELOT GEORGE PRICKETT, FREDERICK LAWRENCE RAWSON, ARTHUR DE SAUBERGUE, WILLIAM SPINKS, HARRY LINDSAY TILLY, Sam TOMLINSON, CHARLES ROWLAND WILLIAMS, and ARTHUR PRESCOTT WOOD.

The discussion upon Mr. HOLT's Paper, "On the Progress of Steam Shipping," was continued and concluded at this meeting.