Boiler Plate

Gear:

GraphiteBearing

Lock Gear, 5 Teeth per Inch

Pipe Brace

22.

4"

Brace Rod Channel

The furnace is mounted on a truck built of channel irons, a pipe framework and boiler plate. The electrode

holders and their working mechanism are mounted on the boiler

plate, and the furnace is

built on this. The electrode holders are aluminum bronze castings and are moved to and fro by means of rightand left-handed screws respectively. The shaft of each screw terminates in a gear engaging with gears mounted on a shaft which passes under the boiler plate base and which has a hand wheel mounted at one end. By this hand wheel one worker can attend to the running of the furnace. The hand wheel shaft is in two parts connected with a coupling and near this is a small collar on the shaft. This arrangement is used to form what we call a "gear lock," which consists of an iron bar held between the collar and the coupling. This bar is hinged and can be dropped down so that the hand wheel shaft may be pushed longitudinally in its bearings sufficiently far to throw the gears out of mesh.

FIG. 1.

Bearing

END VIEW OF FURNACE

As shown in the drawing, the furnace is built up so as to heat the charge in the crucible by radiation from the arc. In our work we generally use a current at 50 volts and 500 to 1000 amperes.

The apparatus can also be used for other kinds of

Shaft

Shaft

Collár Gear Lock

Coupling

Graphite Bearing

Casting

Shaft

5 Teeth

Per Inch

Hand Wheel

furnaces; for example, for heating a crucible embedded in granular carbon. When used in this way convenient electrodes are 4 x 4 in. (10 x 10 cm.) graphitized carbons. Fig. 4, besides showing details of the electrode holder construction, shows modification for use with 4 x 4 in. carbons. The mobility of the electrodes permits of considerable variation in the resistance of the furnace while running with a granular carbon resistor.

The furnace also is convenient for heating the central portion of a horizontal tube embedded in a granular carbon resistor, and, of course,

it may also be used as a furnace in which the tube is heated by an arc on the outside, but in this case the 11-in. (3.8-cm.) electrodes are used.

While there is nothing original in the general principles of the furnace, it is believed that the detail design may be found as useful by others as it has by us, on account of its being so cheap and easy to construct.

FitzGerald Laboratories,

Niagara Falls, N. Y.

Experience With a 91:9 CopperAluminum Alloy

BY A. I. KRYNITZKY*

FTER many experiments in the foundry of the

A Time Fany plant in Petrograd, Russia, with dif

ferent copper-aluminum alloys it was decided to use an alloy containing about 9 per cent of aluminum. It might be stated in advance that with 10 per cent aluminum or more it is very difficult to obtain a homogeneous alloy, particularly with a single melting. In most cases the fracture shows a liquation and also a coarse crystalline structure.

Referring to the equilibrium diagram, these alloys9 to 10 per cent of aluminum-are very close to the point a, (see Fig. 1). We have to expect here the presence of homogeneous alpha solution in the case of annealed alloys containing 9 per cent or less of aluminum; and in the case of 10 per cent or more aluminum, secondary alpha crystals within the primary beta, and also alpha and gamma crystals within original grains of beta.

Formerly chief inspector of time fuses for the Russian Government in the United States; now assistant physicist, Bureau of Standards, Washington, D. C.

Concerning the process of casting, in the first place a well known fact was confirmed, that the temperature of the casting is of great importance. The alloy must be poured at a temperature very near its melting point, which in the absence of a pyrometer is difficult to get because of the formation of a thin film, which makes observation difficult. Chill casting is better than sand casting.

PURITY OF RAW MATERIAL IMPORTANT

The purity of the raw material is, as usual, very important. This fact was confirmed in these experiients with four kinds of copper used: Mansfeld copper, Bare, Tamarack and a Chinese brand. While uni

tioned first three kinds of copper showed very close to 99.6 per cent copper. Analyses of the aluminum were very close to Al 98.81 per cent, Si 0.45 per cent, Fe 0.44 per cent.

All work was done under manufacturing conditions. The alloy was melted and cast in the ingots and then remelted (sometimes more than once) in crucibles, in an oil-fired furnace, a thin layer of charcoal being used to cover the charges to prevent oxidation. For stirring the melts graphite rods were used exclusively.

As before noted, the use of an alloy with 10 per cent or more aluminum is not recommended, since such an

771

pulled on a Mohr and Federhaft machine. The averages of these results are given in Table I.

As to lot No. 21, which was subjected to high, medium and low forging; the difference in the degree of forging was attained by first removing different amounts of skin by means of a sharp die. The less skin removed, the greater the forging subsequently applied.

Concerning lot No. 34 it should be noted that metal cast and quenched immediately in cold water shows less ductility and tensile strength than the same cast when slowly cooled.

To the writer's regret this work, because of circumstances, was discontinued and no more data were obtained. Therefore no positive conclusion can be drawn as to the nature of the peculiarities appearing. Referring to the equilibrium diagram (Fig. 1) it might be said, however, that in both cases (rapid quenching in cold water and slow cooling) we would expect to get only the alpha solution.

Glauber's Salt in Siberian Lakes The following is an estimate of supplies of precipitated Glauber's salt in some of the Siberian lakes: (1) The Great Marmyshansk Lake-144,000,000 poods (2,600,000 short tons) of crystalline salt (Na,SO,10H,O) and 22,000,000 poods (397,210 short tons) of evaporated Glauber's salt; (2) Little Marmyshansk Lake-25,000,000 poods (451,400 short tons) of crystalline salt; (3) Lake Tuskal (Minusinsk district)-up to 100,000,000 poods (1,805,500 tons) of crystalline salt; (4) Lake Varche (Minusinsk district)-up to 100,000,000 poods (1,805,500 tons) of precipated crystalline salt and an enormous quantity of Glauber's salt in solution.

Samples Exhibition to Be Held at Trieste Consul O'Hara cables from Trieste that an announcement has been made of a permanent samples exhibition to be held at Trieste under the auspices of the Chamber of Commerce. A special building will be erected for the purpose, which is expected to be ready by next summer. The consul considers this an excellent opportunity for American exporters to display their goods.

Electrical Treatment of Sewage

Landreth Process*

EVERAL electrolytic methods have been suggested for the purification of sewage. The first to be experimented with, the invention of Webster, was installed at Corness, England, in 1889. In this process the raw sewage flowed in contact with iron electrodes through long troughs; a current of 0.9 amp. was maintained by an e.m.f. of about 2 volts. For treating raw sewage the estimated consumption was 240 lb. of iron and 450 kw.-hr. per million gal. In this process the oxygen liberated at the anode was mostly consumed in oxidizing the iron electrodes; the oxides thus formed acted as a precipitating agent for the sludge of the sewage; the process was therefore chemical rather than electrical. The second process to be experimented with attempted disinfection by means of nascent chlorine liberated by the electrolysis of a soluble chloride. In the earlier installations a chloride was mixed with the sewage and the solution electrolyzed; later sodium hypochlorite produced electrolytically was added to the sewage. In 1893, at Brewster, N. Y., this latter method was used under the direction of the New York City Health Department. About 1600 lb. of salt was used per million gal. and the plant required 700 amp. at 5 volts.

Kennicut, Winslow and Pratt' summarize the electrolytic methods of treatment so far developed as being a question of the cost of supplying the disinfectants and precipitants needed; usually this cost is not in favor of electrolysis in the presence of sewage.

The failure of sedimentation thoroughly to clarify sewage led to the introduction of the chemical precipitation method, and lime was the first precipitant to be used. This method is open to the objection that the addition of too much lime renders varying amounts of the suspended organic matter soluble, which causes the effluent to be more putrescent and obnoxious than that from ordinary sedimentation.

THE LANDRETH DIRECT OXIDATION PROCESS

In the Landreth direct oxidation process for the treatment of sewage, both electricity and lime are employed. The efficiency of the process depends on the combination of these two agents; neither alone produces as good results. Oxygen and hydrogen liberated at the electrodes in the nascent state are claimed to promote the destruction of pathogenic bacteria, also to reduce nitrogenous matter to nitrites, nitrates and carbon dioxide. The presence of lime furnishes an alkaline medium and renders the electrodes passive, thereby reducing the amount of iron going into solution; the lime also assists sedimentation. This process was extensively studied at a 750,000-gal. plant at Elmhurst, L. I., in 1915, later at Decatur, Ill. During the spring of 1918 a million-gal. plant was constructed at Easton, Pa., by Mr. Landreth for demonstration purposes.

DESCRIPTION OF PROCESS

The raw sewage upon entering the plant passes through a coarse screen over a screen having six 0.25in. holes per sq.in., is then elevated by a centrifugal pump passing over a measuring weir to the electrolytic tanks, then through an observation flume and is dis

*Abstract, J. Frank. Inst., vol. 188, No. 2, p. 157. 1Kennicut, L. P., Winslow, C. E. A., and Pratt, R. W.: "Sewage Disposal," 1919, John Wiley & Sons, New York.

charged either through a sedimentation tank or direct to the river.

The electrolytic apparatus consists of a horizontal cypress box 27 ft. 3 in. long, 3 ft. wide and 2 ft. 9 in. deep. The removable top is constructed in two sections and can be made watertight by means of bolts and rubber gaskets. Each section of the top is vented for the removal of the gaseous products of electrolysis. A series of valves at the bottom of the tank serves for the removal of sludge.

6

Internally the tank is divided into eleven spaces, each of which contains two banks of electrodes mounted one above the other, giving a total of 22 banks of electrodes arranged in two horizontal rows of eleven each. These banks of electrodes, each of which consists of 48 plates of mild steel 10 in. by 16 in. by in. spaced in. apart, are placed across the box, the plates being vertical and parallel to the sides. The 48 plates of each bank are electrically connected so that alternate plates have the same polarity, the 22 banks being connected in series. The tank is so constructed that the entire flow of sewage is through the in. spaces between electrodes. Paddles revolve in each of the spaces between electrodes at 20 r.p.m. The total electrode area is 124,287 sq.in. DESCRIPTION OF OPERATIONS

Milk of lime is added at the measuring weir by an apparatus which permits of close regulation, and the amount added is sufficient to give about 30 p.p.m. excess CaO in the effluent. The polarity of the electrodes is changed at regular intervals to reduce polarization. Calcium carbonate tends to crystallize on the electrodes and has the effect of increasing the power required by the stirrers; whenever the power consumption reaches 2000 watts the addition of lime is discontinued. The acid in the raw sewage dissolves these crystals, reducing the power consumption to normal, or to about 1100 watts, when lime is added again at the inlet of the tanks. During this operation lime is added at the observation weir. The voltage of the individual cells ranges from 2.5 to 3.7 volts, averaging 2.82 volts with a current of 34 amp.

EFFICIENCY AND COSTS

The efficiency of any method of sewage treatment cannot well be shown by a tabulation of results, due to the large variation of the raw sewage and to the means of disposal of the effluent; these are determined by local conditions. It is usual to design a plant to meet these conditions. The amount of dissolved oxygen absorbed by an effluent is an important standard; the effluent from the Landreth process is below the most stringent standard in this respect. The average absorption of dissolved oxygen upon standing five days was 0.77 p.p.m., whereas the very strict standard of the Royal Commission on Sewage Disposal allows 30 p.p.m. as a maximum. The effluent produced by the Landreth process is considered highly satisfactory.

A million-gal. plant would consume power at the rate of 335 kw. and 90 per cent lime at the rate of 800 lb. per million gal. A typical plant for treating sewage from a town of 55,000 population can be operated at a cost of 64c. per capita. An "activated sludge" plant would cost $1.10 and an "Imhoff-trickling filter" plant 82c. per capita. A Landreth plant has the additional advantage that it requires only a small ground area and can be operated and installed in a thickly populated district without being offensive.

Effect of Surface Tension on Crystalline Form*

BY CECIL H. DESCH

Professor of Metallurgy in the Royal Technical College, Glasgow

THE

HE investigation which forms the subject of these reports was undertaken at the instigation of Sir George Beilby to test the hypothesis of Quincke, according to which metals and other substances, immediately before solidification from the liquid state, separate into two immiscible liquids, one of which is formed in much smaller quantity than the other. These liquids have an interfacial surface tension, and a foam is formed, the liquid present in smaller proportion arranging itself in cell walls, and the second constituting the cell contents. Crystallization then takes place within the foam cells, and the cell walls are represented in the solid mass by the boundaries of the crystal grains.

If this were actually the case, the form of the crystal grains in a solid metal might be expected to approximate to that of the cells in a foam, such as is produced by blowing air through a soap solution, the shape of the cell walls in both cases being due to surface tension. The subsequent growth of the crystals forming the cell contents might distort the original cells, but could scarcely produce a complete change of type.

THEORETICAL FORM OF FOAM CELLS

The problem of the form of individual cells in a foam has received surprisingly little attention. The fundamental principles were established by Plateau in his classical investigations,' and may be stated as follows:

(a) Only three films can meet in an edge, and they must make equal angles of 120 deg. with each other; (b) Only six films can meet at a point, and adjacent edges must make equal angles of 109 deg. 28 min. with one another.

The foam being the result of surface tension, the area of each cell is necessarily a minimum for the given conditions. The arrangement of the dividing walls in a single layer of bubbles on the plane surface of a liquid is easily shown to be a regular hexagonal pattern.

The beautiful experiments of Plateau did not include the examination of a mass of foam. A solution of this problem was obtained by Lord Kelvin. The most general solution for the homogeneous division of space was shown by him to be a tetrakaidecahedronal cell, consisting of fourteen walls, which may be plane or not plane (Figs. 1 and 2). Eight of these are hexagonal and four quadrilateral, so that there are thirty-six edges and twenty-four corners. Each face is common to two neighboring cells; each edge is common to three cells, and each corner is common to four cells. Any homogeneous assemblage of similarly shaped and similarly oriented objects, however irregularly shaped, may be divided from one another by similar cells of the above type, in such a way that every single object is completely inclosed in one cell. The simplest example of such a cell may be obtained by truncating the six

Second report (slightly condensed) to the Beilby Prize committee of the Institute of Metals on the solidification of metals from the liquid state, presented Sept. 24, 1919. The first was presented to the Institute at the spring meeting of 1914, and consisted of a review of the state of knowledge respecting the solidification of metals from the liquid state.

1J. Plateau, Statique expérimentale et théorique des liquides. 2 vols. Ghent, 1873.

Proceedings of the Royal Society, 1894, vol. 55, p. 1; Collected Papers, vol. 5, p. 333.

corners of a regular octahedron to such a depth that the eight original triangular faces are reduced to equilateral equi-angular hexagons.

arcs.

Foam cells are subject to the further condition that the partitional area must be a minimum. The tetrakaidecahedron of minimum area has been shown to have also eight hexagonal and six quadrilateral faces, all the edges being equal in length; but the latter, instead of being straight lines, are now similar plane The condition being that the edges must meet at an angle of 109 deg. 28 min., each arc is one of 19 deg. 28 min. It is not actually circular, but may be considered as such without serious error. The figure may be constructed very simply by stiff brass wires soldered together to form the required figure. Such a wire model, immersed in soap solution, gives a giant foam cell, the faces of which have the required form. The hexagonal films are doubly curved in such a way that the three diagonals are straight lines lying in one

plane, and the sum of the curvatures in mutually perpendicular normal sections at any point is constant. A mass of foam built up of similar cells of the above shape would be stable.

The rhombic dodecahedron, Fig. 8, is a plane-sided polyhedron, of which each pair of sides meets at an angle of 120 deg., and space may be filled with equal

and similar rhombic dodecahedra. Moreover, it is the only plane-sided polyhedron which fulfills these conditions, but foam cells of this form are unstable, since it involves the meeting of twelve plane films at a point, an unstable equilibrium which may be departed from in three different ways.

EXPERIMENTAL EXAMINATION OF FOAM CELLS

In order to prepare a foam, some solution is poured into a glass trough with plane parallel sides, and air is blown through it by means of a narrow pipette until the trough is filled with foam. When a fairly stable condition has been reached, single cells are examined by placing the trough in front of a window, screening it with a sheet of black paper having a hole about 2 cm. in diameter, so that the attention is more easily concentrated on a single cell. An attempt is then made to count the cell walls, and to record the number of edges of each face. This is done for as many cells. as possible. The direction of curvature of the walls may often be recognized by the arrangement of the bands of color under illumination. A second method consists in making a foam from a warm solution of gelatin, of sufficient concentration to set on cooling. The foam cells are thus fixed, and may be examined at leisure, each cell being cut open and examined in turn by using Both methods have fine-pointed dissecting scissors. been employed in obtaining the results shown below.

Philosophical Magazine, 1887, vol. 24, p. 503; Collected Papers, vol. 5, p. 297.