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Standard Sand for Cement-Testing. GARY.

(Mittheilungen aus den königlichen technischen Versuchsanstalten zu Berlin, 1898, p. 121.)

In Prussia a standard sand for cement-testing has been adopted, but in no other country. The adoption of an international standard sand is desirable, so that, in testing mixtures of sand and cement, the influence of the varying properties of sand might be eliminated.

The Author obtained samples of the sands used in various countries for cement-testing, and made test specimens of 1 cement 3 sand, and 1 cement 5 sand. The sands were obtained from Prussia, the Rhine, Austria, Switzerland, Russia, Norway, France, England and America. They were carefully examined as to specific weight, size of grain, chemical composition, and strength in tension and compression when mixed with Portland cement. The specimens were tested at the ages of 7 days, 28 days, and 90 days. The strengths of the specimens made from the different sands differ considerably, as is to be expected from the different physical properties of the sand; the difference is most marked in compressive tests. The sands with sharp angular grains are strong in tension; those with round grains strong in compression. The Paper is accompanied by numerous tables, diagrams, and sheets of microphotographic reproductions, showing the sand particles.

The "Le Chatelier" Volumometer. C. PIENO.

(Annales des Travaux publics de Belgique, 1898, p. 453.)

A. S.

For some years one of the clauses in French cement specifications has read as follows, "poured slowly into a measure and not heaped up, the cement shall weigh not less than 103 lbs. per bushel." The Author states that the weight per bushel was, for a long time, thought to indicate whether the cement had been properly burnt, and not much account was taken of the fineness of the grinding. He then shows that it is impossible to draw any conclusions as to the extent to which the cement has been burnt from the weight per bushel; but from the specific weight it can be ascertained whether foreign substances have been added, by comparing the density with the known mean density of Portland cement, viz., 3.10.

In order to determine the density, the apparatus most commonly in use on the Continent is the volumometer of Schumann, an illustration and description of which is given. The Author, however, considers it defective in several points, and proceeds to describe an improved volumometer, the invention of Le Chatelier.

It consists of a phial having a capacity of about 120 cubic centimetres (7.32 cubic inches), with a narrow neck about 20 centimetres (7.87 inches) in length. Towards the top of the neck a bulb is formed having a capacity of about 20 cubic centimetres (1.22 cubic inch), a line graven in the glass above and below the bulb exactly marking this capacity. Above the top line the neck is graduated 0 to 3 cubic centimetres in tenths. The diameter of the neck is about 0.01 millimetre (0·39 inch), and the length of neck from the phial to the bulb about 0.10 metre (3.93 inches).

To determine the density of the cement, the apparatus is filled with benzine up to the lower line, and 64 grams (0.1408 lb.) of cement carefully weighed, and poured in little by little. When the benzine rises to the upper line the remainder of the cement is weighed, and the amount subtracted from 64 grams, the difference will represent the weight contained in 20 cubic centimetres (1.22 cubic inch).

After describing another method of determining the density, and mentioning various precautions to be observed in the use of the apparatus, the Author summarizes its advantages, and states that for exactitude, simplicity, and ease in operating, it has no equal. H. I. J.

Test of a Wire Rope 3 inches in Diameter. A. MARTENS. (Mittheilungen aus den königlichen technischen Versuchsanstalten zu Berlin, 1898, p. 89.)

A wire rope 90 millimetres outside diameter was tested at the Royal Testing Laboratory. The rope consisted of six principal strands and a central core. Each principal strand consisted of six secondary strands and a hemp core, while the secondary strands each contained thirty wires in two layers of eighteen and twelve round a hemp core. The rope therefore contained 6 × 6 × 30 = 1,080 wires, each 1.46 millimetre (0.058 inch) diameter. The tensile strength of the wire was 116 tons per square inch, and if the full strength of the individual wires had been obtained, the rope should have had a breaking strength of 330 tons. The rope was bent round two special castings which were attached to the testing machine. One end of the rope was lashed by three pairs of screw clamps, each with eight bolts 2 inches diameter; the other end was spliced. Great difficulty was experienced with the clamp fastenings, owing to the contraction of the rope as the load increased. The circumference was 288 millimetres before the application of the first load, and shrank to 252 millimetres with 150 tons load. The rope ultimately broke near the end of the splice with a load of about 250 tons, giving a coefficient of strength 0.75. A. S.

Experiments on the Emission of Air through Divergent Conical Nozzles. A. FLIEGNER.

(Schweizerische Bauzeitung, 1898, p. 68 et seq. 14 Figs.)

The experiments described in this article were suggested by a consideration of the construction of the De Laval steam-turbine. In this apparatus a special nozzle is used, consisting of a taperpipe, with the sharp entrance edge rounded off and the outlet end made parallel for a certain distance. In certain published accounts of the turbine it had been stated that a nozzle of the described form caused a reduction in the pressure of steam from that in the pipe to that in the turbine chamber, and that the steam issued from it in the form of a well-defined jet. It was also stated, that in this way the velocity of the jet reached 3,280 feet per second, while with a well-rounded edge the velocity attained was barely half as great. Nothing was stated, however, as to the method of experiment adopted, and the Author believes it was taken for granted that adiabatic expansion occurred. He considered the conclusions doubtful, and decided to make special tests, but being unable to use steam he experimented with air, using the air-pressure apparatus at the Zurich Polytechnic. Two precisely similar nozzles were used. The inlet end was rounded and the nozzle was first bored out parallel and then more and more conical, and tests made after each operation. A piece 3.94 inches long next the inlet was left parallel, but no parallel outlet was left, as in the De Laval nozzle, as it was difficult to arrange, and the Author considered it had no effect. In the tables of results the diameter of the emission end only is given. The pressure was measured at three places in the length through orifices 1 millimetre (0.039 inch) diameter. After a detailed description of his method of experimenting, the Author gives a series of elaborate curves and tables, and in conclusion points out that his doubts proved well founded. The average pressure in the plane of the outlet of the nozzle never sinks to that of the surrounding pressure.

The statement that adiabatic expansion takes place is also incorrect. In the case of elastic fluids an increase in the crosssection of the nozzle causes an increase of resistance; if then it be desired to produce the greatest possible emission velocity, the cross-section must be increased as little as possible, just as is the case with dripping tubes. The same laws apply to steam, and the Author concludes, that with the present boiler pressures, an emission velocity of 3,280 feet per second is absolutely impossible.

E. R. D.

Experiments on a Flexible Joint for Riveted Framing.

MESNAGER.

(Annales des Ponts et Chaussées, 1898, p. 300.)

The Author points out that in tests made on a large number of bridges on the French railways it has been found that the secondary strains frequently attain to 25 per cent. to 30 per cent. of the principal strains. In a previous Paper1 he proposed an arrangement of jointing for lattice girders which would reduce to a negligible quantity these secondary strains, and in the present Paper he describes some experiments made upon a bridge-panel or bay, built upon this system, of the largest dimensions which could be tested in the laboratory of the School of Bridges and Roads.

This experimental panel, measuring 9 feet 6 inches in height by 11 feet 7 inches in length, corresponded to a portion of a girder of an 82-foot-span bridge, and was subjected to a series of tests, which were carried up to breaking-point. A Plate with three Figs. gives full dimensions of the members of the girder and their arrangement. The secondary members of the girder are formed of a plate stiffened by angle-bars, which are cut off short of the point of junction with the main girder at a distance about fifteen times the thickness of the plate, which plate is continued on and riveted to the main girder, the free portion of the plate forming the flexible joint.

The panel was tested on its side, i.e., with the uprights horizontal, and the pressure transmitted from the four jaws of the machine through horizontal knife-edges. Arrangements were also made by which a bending strain and also an angular pressure could be put upon the panel, both of which corresponded to the pressure which would be taken by a bridge under ordinary conditions of working.

By means of two telescopes fixed upon one of the main uprights as close as possible to the centre line of the panel, readings could be taken on a scale fixed on the other upright, and the least angular deformation could easily be read.

A Table gives full details of each experiment, from which the following deductions are made :

In order to have the maximum resistance it is necessary— (1) To use a plate the whole width of the joint, and not two plates joined together.

(2) To stiffen by transverse angle-bars up to the limit of the free part of the joint.

(3) To bring the rivets joining the flexible plate to the main girder, as close to the edge as possible.

Since making these experiments a bridge of 131 feet span, to be

1 Annales des Ponts et Chaussées, 1896, part 2, p. 750.

constructed on the principles described, has been approved by the Minister of Public Works, and the details of the design are shown in seven Figs.

The Paper is illustrated by Figs. in the text and three Plates.

H. I. J.

The Use of Jointed Members in Roof-Construction.
A. KIELBASINSKI.

(Schweizerische Bauzeitung, 1898, p. 38. 7 Figs.)

In the machine building of the Geneva Exhibition of 1896 a little-known type of roof-construction was used, which depends upon the principle of jointed members, such as have long been in use in bridge-work. Professor Jules Gaudard in 1896 published, in "Le Génie Civil," an account of this type of roof, with calculations, and he states that it was first used at the Chicago Exhibition. The Author points out, however, that the construction has been used in St. Petersburg since 1892, and was employed for the first time by Professor Jasinski for the new locomotive shops of the Nikolai Railway and for other buildings since that time. The Author shortly states the principle, and then illustrates it by sketches of a roof covering a building, 133 feet wide, divided into three bays by two rows of columns, the two side bays being each 43.3 feet wide and the centre bay 46.4 feet wide. The framework of the roof consisted of two independent triangular systems with a triangular system forming the apex of the roof resting upon the free ends of both side systems. The principals were placed at 10.3 feet centres, and the ends of alternate principals were supported upon the stanchions. The columns were set 20.6 feet apart in a longitudinal direction. The triangular framework at the apex of the roof forms the lantern and rests upon the ends of the side systems. In the system as first designed the lantern part was a rigid three-cornered frame, but now it is madeof linkwork. The advantages of the latter arrangement are: (1) that the weight of the lantern frame produces a horizontal thrust on the side members in the opposite sense to that produced by the horizontal component of the wind-pressure; (2) by this system alone is it possible to distribute the wind-pressure on to both side walls through the principal rafters. Details of construction are shown in the figures.

E. R. D.

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