ENGINEERING MAGAZINE. COMMENCED JANUARY, 1869, Published on the 15th of the month at $5.00 per year. The January number of this MAGAZINE, for the year 1881, begins the Twenty-fourth Volume. Beginning as Eclectic Journal, and presenting almost exclusively matter selected from current literature, it has gradually become the chief medium through which the leading writers on engineering subjects can best present their original essays to American readers. The attitude of the MAGAZINE has been, and will continue to be, that of a journal of original and selected papers upon subjects relating to modern advanced Engineering. Theoretical and Practical Essays are alike presented in its pages, although the latter largely out-number the former, as best suited to the tastes and demands of the Americal Engineers. Some of the most valuable contributions to the literature of technical science within the last few years have been first presented in these pages. Among the more extended original contributions to the later volumes may be cited new contributions to Graphical Statics-Transmission of Power by Wire Ropes-Maximum Stresses in Framed Bridges-Momentum and Vis Viva-Rapid Methods of Laying out Gearing-Transmission of Power by Compressed Air-Geographica. SurveyingMathematical Theory of Fluid Motion Thermodynamics - Practical Theory of Voussoir Arches-Cable Making for Suspension Bridges, &c., &c. To the above may be added the following valuable essays, translated from foreign sources, which have first appeared in these pages: Linkages and their ApplicationsThe Origin of Metallurgy-and The Theory of Ice Machines. The plans for future volumes comprehend many improvements in the same direction. The wants of the educated practical engineer, who desires to keep in the foremost rank of his profession will be steadily kept in view, and our constantly increasing resources for supplying the best of scientific information will be employed to secure such result. Cloth covers for Volumes I. to XXIII. inclusive, elegantly stamped in gilt, will be furnished by the publisher, for fifty cents each. If the back numbers be sent, the volumes will be bound neatly in black cloth and lettered, for seventy-five cents each. The expense of carriage must be borne by the subscriber. Notice to New Subscribers.-Persons commencing their subscriptions with the Twenty-fourth Volume (January, 1881), and who are desirous of possessing the work from its com mencement, will be supplied with Volumes I. to XXIII. inclusive, neatly bound in cloth, for $60.00. in half morocco, $90.00. Notice to Clubs.-An extra copy will be supplied gratis to every Club of Five subscriber, at $5.00 each, sent in one remittance. ROMAN BUILDING IN ENGLAND AND IN ITALY.. GAS AND ELECTRICITY AS HEATING AGENTS. By Dr. C. English Mechanic.. 458 465 469 .Proc. Amer. Acad. Arts and Sciences.. 473 ..Iron..... THE EFFECT OF PUNCHING ON STEEL AND IRON PLATES... Engineer.. 477 487 .Trans. from l' Electricien... 490 491 OUR CENTER OF POPULATION. By Frank D. Y. Carpenter, Written for Van Nostrand's Magazine, 496 RECENT ADVANCES IN ELECTRIC LIGHTING. By W. H. NEW MODE OF COMPENSATING BALANCES. (Illustrated). By 502 .Journal of Society of Arts...... 504 512 Paper read before Boston Soc. Civil Eng. 517 PARAGRAPHS.-The Tunis side of the St. Gothard Tunnel, 449; Arrival of Clyde laborers, 457; Persons who ca not recover for injury on R. R. cars, 501. REPORTS OF ENGINEERING SOCIETIES.-American Society of Civil Engineers, 518; Engineer's Club of Phila delphia, 519. ENGINEERING NOTES.-Railway boring near Abbott's Cliff, England, 519. RAILWAY NOTES.-Mountain Railways, 519; Observations on fractures of steel rails, 520, IRON AND STEEL NOTES.-Stock of the North British Railway Co.; Dividend of the North British Railway Co. Concrete slag a substitute for stone, 520, ORDNANCE AND NAVAL.-Machine Guns at Shoeburyness, 520; The Russian Navy, 521. BOOK NOTICES.-Publications Received; Graphical Determination of Forces in Engineering Structures, by Jame B. Chalmers, C.E.; Practical Organ-Building, by W. E. Dickson, M.A.; Induction Coils, How Made and How Used The Plumber and Sanitary Houses (second edition), by S. Stevens Hellyer; The Wool Carder's Vade Mecum, b William Calvert Bramwell; Lathe Work, by Paul N. Hasluck; Steam Boilers, by William H. Shock, Engineer-in Chief, U. S. N.; The Telescope, by Thomas Nolan, B. S., 522. MISCELLANEOUS.-The Corrosion of Iron in Boilers; The Great Brush Light; Experiments on the Electric Curren Boudet's Microphone, 524. VAN NOSTRAND'S ENGINEERING MAGAZINE. NO. CXLX.-JUNE, 1881.-VOL. XXIV. A RATIONAL SYSTEM OF PISTON PACKING. By S. W. ROBINSON, C. E., Professor Mechanical Engineering, Ohio State University, Columbus. Read before the American Society of Mechanical Engineers, May Meeting, Hartford, Conn. Contributed to VAN NOSTRAND'S ENGINEERING MAGAZINE. THE primary object of a good piston against its packing glands; and that im packing is evidently to prevent the work- view of these facts it may be desirable ing fluid from escaping past the piston. to introduce a groove containing a solid, The sole object of the present paper is stout half ring about at the middle of to investigate how this can be done most the face of piston to serve as a carriage, efficiently; leaving out of the question with the piston properly jacked upon it: all such uses of packing as making it and, finally, that all these devices may serve the purpose of a carriage for sup- be replaced by a considerable breadth of port of the piston, &c.; except, perhaps, piston rims for support of piston, and a reference to this matter of carriage narrow packing rings under outward support-in that it seems desirable to pressure to prevent escape of working have a carriage for the piston, especially fluid. This is all the more evident when in horizontal engines, and where the we reflect that the piston may be made cylinder has been bored out larger than light-hollow, if necessary, for this end, the piston to correct irregular wear after and the weight added to the cross head some use. But a glance at the matter or the connecting rod-in which event will show that for the packing to serve the piston and cylinder will be subjected as carriage, it must be very wide in order to the least possible wear, and thus to present the necessary wearing surface scarcely need re-boring within the life of for durability, and that where the pack- the engine. It is evident that this result ing is wide, the rims of the piston must is preferable to that where the cylinder be correspondingly narrow, and be ac- frequently gets out of form to the extent cordingly unfitted for bearing the weight necessitating repeated re-boring, when of the piston; and that the flexibility of the lifetime of the engine will be more or the packing rings will allow them to less afflicted with "piston blowing." take a somewhat irregular form, thus Hence, it is proposed, here, to adopt tending to wear the cylinder out of as light a piston as possible, to use very round; and that the devices for setting narrow packing rings, and wide rims on out the rings may change in intensity the piston, especially for horizontal enof action so as to cause the piston to ride gines. The simplest possible packing upon the cylinder at some side, causing consists of a single ring split upon one relatively rapid wear of the narrow rims side. The simplest piston is one in a of piston; and that the piston rod will single piece, possibly cast hollow for thus be brought into wearing contact securing desirable form. Hence, a sinVOL. XXIV.-No. 6-31. gle ring, sprung into a groove turned on the radius of the ring. To define it clearly, the face of such a piston, combines the draw a line parallel to BO and very near elements of simplicity. Two or more to B as at C. Suppose these lines fixed rings may, however, be used on a single to the ring, and parallel before flexure. piston, each sprung into its own groove. After flexure these lines will intersect at We will now investigate the single- some point more or less remote from B, ring packing. It will appear afterwards according to the amount of bending. that, to set the ring out by pressure of The distance from B to the point of inthe working fluid transmitted to the un- tersection is p. It is evident that if the derside of the ring through holes, causes ring is of circular form before flexure, and excessive frictional contact of the ring also after, p will be of constant length upon the surface of cylinder. It would for all parts of the ring. As the ring is seem desirable, therefore, to give the most conveniently made of circular form, ring its pressure of contact by means of and as it will be used in a circular cylinthe inherent stiffness of the ring itself, der, it is desirable that the thickness by turning it larger than the cylinder shall so vary as to realize this and make bore. p constant. A ring, split upon one side and pressing outward with a constant pressure, as it evidently should for greatest efficiency, will necessarily be thicker at points opposite the split, as shown in Fig. 2. FORM OF PACKING RING. To find the law of varying thickness, let AB, Fig. 1, represent a piece of such a packing ring, the end or split being at According to the theory of flexure, the flexural moment must equal the moment of the applied forces. This latter will, in the present case, be the resultant moment of all the normal pressures on AB. Let P represent the normal pressure per unit of surface of the ring against the cylinder, and if b be the breadth of ring, the pressure per unit of length of ring will be Pb, and for a length rde, the pressure will be Pb.rde. The moment of this element will be Pbrdo.r sin with reference to an origin of moments at B, where the origin is taken for eq. (1). The integral of this, for between the limits x and o, will give the total moment of the forces acting on the part AB, or varied EI Ez p 12p = =2Pr2 sin 2 A. Then the normal pressure of the and ring against the cylinder along the outside of AB will be due to a flexural mo- At the middle of ring, or where AB= ment, or resistance to bending, of the 180°, we have section of ring at B. This, according to the theory of flexure, will be ρ Ez,3 =2Pr 12p, sin22 P1 (3) ρ where E is the coefficient of elasticity of the material of the ring, I the moment of an equation for the whole ring, and givinertia of the section of ring at B, and ping the relation between 2, p and x; upon the radius of curvature due to the bending. any one of which we may impose arbitrary This radius is not to be confounded with conditions, the other two remaining mu |