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To Repair Old 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. 0. 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,

122 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



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 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 of its use?—R. T. J.

H н

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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,

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

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current used. This is an inducement For work other than round, a dog such for the customer to use a few lights or as that shown in Fig. 2 may be used. small power for a long time, rather than The work is placed between the jaws, a large amount for a short time.

and held in position by the bolts. The In electric power plants extra appa- holes in the upper jaw are made larger ratus is often needed to take care of the than the screws in order that the angle large load which is thrown on the sta- between the jaws may be varied. The tion at certain times of the day. This connection between the face plate and apparatus is in operation, usually, for dog is made as with Figure 1. only a few hours a day and for the remaining time is idle, not earning money,

“Extra Current" while the interest on the money invested in it continues.

Will you please explain how self-induction

produces an extra current? 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 consune from their apparatus,

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Lathe Dogs
What are lathe dogs ?—R. H. H.
As the frictional contact of the work

Suppose two boys, Ned and Sam, to on the live center is not sufficient to turn

face each other, holding a stout spiral it, some device must be used to make the work turn with the center. To ac

spring between them. Each boy atcomplish this a lathe dog is used. For

tempts to revolve this solenoid about its

axis, clockwise. The first effect is that round work, such as shafting, a dog like that shown in Fig. 1 is often used. The

the spring will absorb some of the enshaft or piece to be turned is placed

ergy, expended by the two boys, in proin the hole A, and held firmly in place by ducing a torsion, stress, or strain in the the set screw B. The tail-piece C is put

spring. If their exertions be equal a through a hole in the face plate and the

state of equilibrium will soon be reached work rotates with the live center.

and.the solenoid will remain at rest. If While this type of dog is satisfactory

Ned exerts the greater strength the

solenoid will revolve anti-clockwise, as in most cases, the fact that the contact between the dog and the face plate is appearing to Sam, and energy will be

transmitted along the axis of the solenoid beyond the end of the piece, introduces a bending strain which is appreciable in

from right to left. Now when Ned gets slender work. To avoid this, dogs are

tired and reduces his strength until the

coil ceases to revolve, and then Sam made with a straight tail, and driven by a stud projecting from the face plate.

“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.




Lining Shafting

in suitable bases and connected by a rubWhat is the best method of lining shafting ? ber tube. When the rubber tube is filled --). W. S.

with water, and the glass tubes placed In equipping a shop, the first work of vertically on the shaft, the fluid should the machinist is the erection of the shaft

stand at the same gradation in each glass. ing. The main line should be the first

These levels are made with self-acting laid out, and the engine, together with valves to prevent the escape of the fluid. the jack and countershafting, must be

When pulleys or hangers make the located from it. After placing the

direct application of a level to the shaft impracticable, leveling hooks, in connec

tion with a wooden straight-edge, as SHAFT

shown in Fig. 1, are very convenient.

These may be made of wood or metal, STICK FOR LINING SHAFTING,

and of lengths suitable to the case in

hand. hangers as nearly as possible in a horizontal line, the shafting should be placed

Wiring for Bells in the boxes and attached to the hangers.

Please give a diagram showing how three For lining the shaft, a level and a fine

bells may be arranged to ring separately from grass or silk line are indispensable. The each of three push buttons and simultaneously line is tightly drawn, horizontally, a

from a fourth; only three wires are to be

used ?-C. P. M. short distance from the position it is desired that the shaft shall occupy, and the distance from the surface of the shaft

8 to the line is measured and made equal near each hanger by a stick such as is 9 shown in Fig. 202. The level is used to make the shaft

2 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 used by driving a nail into the end of the stick to allow some adjustment. The level is used as before.

Connect the bells as shown in the diaWhen the distance is great, or obstacles prevent the use of the stick as

gram, making the resistances such that

the battery will ring a bell through any suggested, a line may be drawn on the floor of the shop by dropping a plumb series.

one of them but not through two in line from near the ends of the first shaft and connecting the points located. Another line, directly under the desired

Use of Cylinder Oil location, may be drawn by direct meas- Question: Should cylinder oil be used in urement, and the second shaft erected by

air-compressor cylinders?--C. W. dropping a plumb line to this second floor Answer: As there are a number of line near the ends of the second shaft. cases on record where accidents have ocThis method may be employed, with such curred from explosions in air-compressor variations as the case may demand, even cylinders, due to the use of too much oil though a floor or wall be between the for lubrication and to consequent ignilocations.

tion of the resulting oil-vapors mixed In leveling up long lines, or around with air on compression, the use of soapmachines, or through walls, the hydro- suds for lubrication instead of cylinder static level is a most convenient tool. It oil, either entirely or at stated intervals, consists of two graduated glass tubes set is a means of avoiding such accidents.

may be



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Power Factor

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Joining Leather to Iron

forged is comparatively slight, running Question: How can leather be glued to from a good red heat to a yellow heat. iron?-B. E. S.

Some grades of self-hardening steel may Answer: To glue leather to iron, paint be annealed by heating the steel to a the iron with some kind of lead color- high heat in the center of a good fire say white lead and lampblack. When and allowing the fire and the steel to cool dry, cover with a cement made as fol- off together. Steel which has been anlows: Take the best glue procurable; nealed in this way may be hardened by soak it in cold water till soft; then dis- heating to the hardening heat and cooling solve in vinegar with a moderate lieat, in oil. and add one-third of its bulk of white Self-hardening steel is used to a large pine turpentine. Thoroughly mix, and extent in modern practice for lathe tools, by means of vinegar make it the proper much being used in the shape of small consistency to be spread with a brush. square steel tools held in special holders. Apply the cement while hot; draw the

Such a tool is shown in the accompanyleather on or around quickly; and press ing figure.

. tightly in place. In case of a pulley, draw the leather around tightly as possi

Power Factor Meter ble ; lay and clamp.

What is a power-factor meter? How is it

connected to a three-phase circuit?-D. S. L. 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, gen

Transformer erally 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

Power-FACTOR METER. 40 cents and upwards per pound, some A power-factor meter is an instruof the more expensive grades costing ment for indicating the power factor of $1.00 or so. When in use, self-harden

an alternating current circuit the ing steel will stand a much higher cutting phase relation of current and electromospeed than the ordinary so-called carbon tive force. steel. For this reason it is much more The usual way to connect a powereconomical to use, although its first cost

factor 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 trans

former may or may not be necessary, acSelf-HARDENING STEEL TOOL.

cording to the potential between A and

B. Leads c, d and e are connected to is higher. Self-hardening steel cannot what is virtually a two-phase induction be cut with a cold chisel and must be motor, in the interior of the powereither cut hot or nicked with an emery factor meter. It is this motor that, parwheel and snapped off. Great care must tially counter-balanced by the shunt coil be used in forging it, as the range of in the interior of the meter, gives torque temperature through which it may be to the dial pointer.



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