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To Repair Oid Masonry

Why Boilers Explode How is old masonry to be repaired when Can you give any reason for a boiler exto be connected with new ?-C. R. D.

ploding shortly after being tested ?–M. O. P. The mortar of the old should be There is good reason for believing that thoroughly cleaned off wherever it is most of the mysterious explosions of injured along the surface where the boilers which stand the Inspector's test, junction is effected, and the surface thor- and then explode at a much less pressure, oughly wet. The bond and other arrangements will depend upon the circumstances of the case ; the surfaces connected should be fitted as accurately as practicable, so that by using but little mortar, no disunion may take place from settling.

An expedient, very fertile in its applications to hydraulic constructions, has been for some years in use among the French engineers, for stopping leaks in walls and renewing the beds of foundations which h a ve yielded, or have been otherwise removed by the action of the water. It consists in injecting hydraulic cement into the parts to be filled, through holes drilled through the masonry, by means of a strong syringe. The instruments used for this purpose, as shown in the figure, are usually cylinders of wood or of cast iron; the bore uniform, except at. the end, which is terminated with a nozzle of the usual conical form; the piston is of are due to the weakening effects of unwood and is driven down by a heavy mal- equal expansions, for a boiler that will let. In using the syringe, it is adjusted stand a hundred pounds test this week to the hole; the hydraulic cement in a cannot explode next week at fifty pounds semi-fluid state poured into it; a wad of pressure, unless it has suddenly become tow, or a disc of leather being introduced wonderfully reduced in strength, and no on top, before inserting the piston. The corrosion or other natural cause, with cement is forced in by repeated blows which we are acquainted, save expanon the piston.

sion, can produce this result. When we Sand should be avoided in the mortar consider that strains from difference of for injections, as it is quite likely to cause expansion are generally greatest when trouble by settling to the bottom of the firing up, and when there is no pressure syringe and preventing the formation of in the boiler, we can see that the time a homogeneous mass.

may arrive when a crack is started or

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METHOD OF RETAINING OLD MASONRY.

the parts weakened, so as to give way under a moderate pressure just after the test has been made; and this is the probable reason why so many boilers explode

why so many boilers evolode in getting up steam, or so soon after, or upon pumping in cold water, or, even, as in a recent case in England, while cooling off.

Wright Demand Meter We have an electric discount meter installed in our home. Would you kindly give an explanation of its operation and reason an, of its use?—R. T. J.

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A Portable Bookcase Can you tell me how to make a bookcase that can be easily taken apart-without the use of nails or glue?-C. S. H.

Provide upon the ends of the shelves a tongue, or tongues, long enough to pass through the thickness of the sides and reaching to one inch beyond. Each side must be pierced with apertures to permit of this, and the tongues also are pierced, each one with a square hole. When the tongues at the ends of the shelves are pushed through the mortises in the sides, all that requires to be done to make a firm structure is to insert pegs in the holes in the tongues, every part being thus interlocked immovably. The general appearance of the set of shelves is not impaired by the arrangement just described—indeed, it is suggestive of a very neat and compact piece of work,

Wright DEMAND METER.

The Wright demand, or discount, meter is used in connection with a watthour meter. It registers the maximum amount of current used on the line in which it is installed. The theory of its operation is as follows.

A sealed glass tube of the shape shown in the figure is partly filled with a suitable liquid “L.” Behind the tube "s" is placed a scale; "A" is an air chamber, “H” a bulb, about which is wound a coil of wire of such resistance that an increase in current strength will cause a large rise in temperature. The heat, due to the current passing, causes the air to expand in bulb “H” and forces the liquid up in the right tube. If the temperature is high enough it will force some of the liquid over into the tube “S.” The greater the current passing, the greater the temperature rise and the larger the quantity of liquid forced into tube "S.” Therefore the liquid in tube “S” is a measure of the maximum current strength used. The scale behind “S” serves as a convenient indicator of the current registered in tube "S.".

The customers bill is figured as follows.

Suppose for the first thirty hours the maximum amount of current is charged for at the rate of fifteen cents a kilowatthour and the remaining amount at ten cents a kilowatt-hour. For the same number of kilowatt-hours a bill will be less, the smaller the maximum amount of

FRONT AND SIDE ELEVATION OF PORTABLE BOOKCASE,

The case may be taken apart for packing.

especially if the ends of the tongues are deprived of all their sharp corners, and if the front edges of the sides are stopchamfered.

For work other than round, a dog such as that shown in Fig. 2 may be used. The work is placed between the jaws, and held in position by the bolts. The holes in the upper jaw are made larger than the screws in order that the angle between the jaws may be varied. The connection between the face plate and dog is made as with Figure 1.

current used. This is an inducement for the customer to use a few lights or small power for a long time, rather than a large amount for a short time.

In electric power plants extra apparatus is often needed to take care of the large load which is thrown on the station at certain times of the day. This apparatus is in operation, usually, for only a few hours a day and for the remaining time is idle, not earning money, while the interest on the money invested in it continues.

By the use of a discount meter customers, whose use of current cause this apparatus to be installed are made to pav more, according to the amount of current they consunie from their apparatus,

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Lathe Dogs
What are lathe dogs?R. H. H.

As the frictional contact of the work on the live center is not sufficient to turn it, some device must be used to make the work turn with the center. To accomplish this a lathe dog is used. For round work, such as shafting, a dog like that shown in Fig. 1 is often used. The shaft or piece to be turned is placed in the hole A, and held firmly in place by the set screw B. The tail-piece C is put through a hole in the face plate and the work rotates with the live center.

While this type of dog is satisfactory in most cases, the fact that the contact between the dog and the face plate is beyond the end of the piece, introduces a bending strain which is appreciable in slender work. To avoid this, dogs are made with a straight tail, and driven by a stud projecting from the face plate.

Suppose two boys, Ned and Sam, to face each other, holding a stout spiral spring between them. Each boy attempts to revolve this solenoid about its axis, clockwise. The first effect is that the spring will absorb some of the energy, expended by the two boys, in producing a torsion, stress, or strain in the spring. If their exertions be equal a state of equilibrium will soon be reached and the solenoid will remain at rest. If Ned exerts the greater strength the solenoid will revolve anti-clockwise, as appearing to Sam, and energy will be transmitted along the axis of the solenoid from right to left. Now when Ned gets tired and reduces his strength until the coil ceases to revolve, and then Sam "lets go,his end of the coil will tend to continue the rotation in the same direction, and, in so doing, gives up the energy stored as torsion or strain. If Sam is a little careless he may get a jab in the hand, or a bad “kick.” Just so a wire, carrying a current, has a certain amount of energy stored in its surrounding field, which, at the moment when the circuit is opened, is given back as an "extra current.” Its strength will depend upon the conditions; if a highly charged and large electro-magnet be included in the magnetic field of the circuit, the effect of the extra current may be highly destructive.

LATHE Dogs.

Lining Shafting What is the best method of lining shafting? --J. W. S.

In equipping a shop, the first work of the machinist is the erection of the shafting. The main line should be the first laid out, and the engine, together with the jack and countershafting, must be located from it. After placing the

in suitable bases and connected by a rubber tube. When the rubber tube is filled with water, and the glass tubes placed vertically on the shaft, the fluid should stand at the same gradation in each glass. These levels are made with self-acting valves to prevent the escape of the fluid.

When pulleys or hangers make the direct application of a level to the shaft impracticable, leveling hooks, in connection with a wooden straight-edge, as shown in Fig. 1, are very convenient. These may be made of wood or metal, and of lengths suitable to the case in hand.

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Wiring for Bells Please give a diagram showing how three bells may be arranged to ring separately from each of three push buttons and simultaneously from a fourth; only three wires are to be used?-C. P. M.

hangers as nearly as possible in a horizontal line, the shafting should be placed in the boxes and attached to the hangers. For lining the shaft, a level and a fine grass or silk line are indispensable. The line is tightly drawn, horizontally, a short distance from the position it is desired that the shaft shall occupy, and the distance from the surface of the shaft to the line is measured and made equal near each hanger by a stick such as is shown in Fig. 202.

The level is used to make the shaft horizontal, and, if the hangers are adjustable in two planes, the operation is quite rapid.

When other shafting is to be erected parallel to the first, if the distance does not exceed twelve or fifteen feet, a long stick such as shown in Fig. 1 may be used by driving a nail into the end of the stick to allow some adjustment. The level is used as before.

When tlie distance is great, or obstacles prevent the use of the stick as suggested, a line may be drawn on the floor of the shop by dropping a plumb line from near the ends of the first shaft and connecting the points located. Another line, directly under the desired location, may be drawn by direct measurement, and the second shaft erected by dropping a plumb line to this second floor line near the ends of the second shaft. This method may be employed, with such variations as the case may demand, even though a floor or wall be between the locations.

In leveling up long lines, or around machines, or through walls, the hydrostatic level is a most convenient tool. It consists of two graduated glass tubes set

WIRING FOR BELLS,

Connect the bells as shown in the diagram, making the resistances such that the battery will ring a bell through any one of them but not through two in series.

Use of Cylinder Oil Question: Should cylinder oil be used in air-compressor cylinders!--C. W.

Answer: As there are a number of cases on record where accidents have occurred from explosions in air-compressor cylinders, due to the use of too much oil for lubrication and to consequent ignition of the resulting oil-vapors mixed with air on compression, the use of soapsuds for lubrication instead of cylinder oil, either entirely or at stated intervals, is a means of avoiding such accidents.

Joining Leather to Iron Question: How can leather be glued to iron ?-B. E. S.

Answer: To glue leather to iron, paint the iron with some kind of lead colorsay white lead and lampblack. When dry, cover with a cement made as follows: Take the best glue procurable; soak it in cold water till soft; then dissolve in vinegar with a moderate heat, and add one-third of its bulk of white pine turpentine. Thoroughly mix, and by means of vinegar make it the proper consistency to be spread with a brush. Apply the cement while hot; draw the leather on or around quickly; and press tightly in place. In case of a pulley, draw the leather around tightly as possible; lay and clamp.

forged is comparatively slight, running from a good red heat to a yellow heat. Some grades of self-hardening steel may be annealed by heating the steel to a high heat in the center of a good fire and allowing the fire and the steel to cool off together. Steel which has been annealed in this way may be hardened by heating to the hardening heat and cooling in oil.

Self-hardening steel is used to a large extent in modern practice for lathe tools, much being used in the shape of small square steel tools held in special holders. Such a tool is shown in the accompanying figure.

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Self-Hardening Steel What is self-hardening steel and for what is it used ?-S. B. T.

Hardening steel, as its name indicates, is almost self-hardening in nature, generally the only treatment that is required to harden the steel being to heat it red hot and allow it to cool. Sometimes the steel is cooled in an air blast or is dipped in oil. It is not necessary to “draw the temper.” The self-hardening quality of steel is given to it by the addition of Chromium, Molybdenyum, Tungsten, or one of that group of elements, in addition to the carbon which ordinary tool steel contains. Self-hardening steel is comparatively expensive, costing from 40 cents and upwards per pound, some of the more expensive grades costing $1.00 or so. When in use, self-hardening steel will stand a much higher cutting speed than the ordinary so-called carbon steel. For this reason it is much more economical to use, although its first cost

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Power-FACTOR METER. A power-factor meter is an instrument for indicating the power factor of an alternating current circuit or the phase relation of current and electromotive force.

The usual way to connect a powerfactor meter to a three-phase circuit is shown in the diagram. A, B and C are the three phases of the three-phase circuit. Only two series transformers, a and c, are necessary. The shunt transformer may or may not be necessary, according to the potential between A and B. Leads c, d and e are connected to what is virtually a two-phase induction motor, in the interior of the powerfactor meter. It is this motor that, partially counter-balanced by the shunt coil in the interior of the meter, gives torque to the dial pointer.

Self-HARDENING STEEL Tool.

is higher. Self-hardening steel cannot be cut with a cold chisel and must be either cut hot or nicked with an emery wheel and snapped off. Great care must be used in forging it, as the range of temperature through which it may be

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