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Are you worried by any question in Engineering or the Mechanic Arts? Put the question into writing and mail it to the Consulting Department, TECHNICAL WORLD MAGAZINE. We have made arrangements to have all such questions answered by a staff of consulting engineers and other experts whose services have been specially enlisted for that purpose. If the question asked is of general interest, the answer will be published in the magazine. If of only personal interest, the answer will be sent by mail, provided a stamped and addressed envelope is enclosed with the question. Requests for information as to where desired articles can be purchased, will also be cheerfully answered.

To Make Handy Truck

Can you suggest how to construct a cheap, handy truck for moving timbers, stoves, etc. The incline should be very slight.-H. M. K.

A HANDY TRUCK.

Turn a roller 4 inches in diameter and 12 inches long. Through this, bore a hole for the axle, about 3/4 inch in diameter. Take two side pieces, as shown in the drawing, cut from a single 2-by-4inch plank, and at the angle indicated. For the top, nail on boards 16 inches wide, and an inch thick. The truck need be no longer than 18 or 20 inches. A 34-inch piece of round steel or iron should be used for the axle.

Starting with the contact-breaker, which is grounded, the circuit passes to the single-pole double-throw switch; then through one of the sets of batteries, depending upon the position of the switch. The wires from the batteries unite, and pass to one side of the primary of the spark coil. The other side of the primary is grounded, the circuit being completed to the contact-breaker in this manner. One secondary wire passes to one terminal of the spark plug, which is insulated from the plug itself. The other sec

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Wiring for Spark-Coil

How would you wire two sets of batteries for an automobile runabout so that either set could be thrown into service by means of a switch?-H. W. S.

A simple way of doing this is shown. in the accompanying sketch. The circuit may be traced out as follows:

SWITCH

WIRING FOR TWO SETS OF BATTERIES.

CONTACT
BREAKER

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When you hold the open end of the receiver close to the transmitter of a telephone, why do you hear a loud, shrill hum?-H. E.

This does not always take place; but when it does, it is due to the following action:

If the diaphragm of the transmitter is of iron, then, when the receiver is brought near it, the permanent magnets in the receiver will attract the transmitter diaphragm. This will alter the resistance of the transmitter circuit of the phone, inducing a current in the secondary circuit, which will act upon the receiver diaphragm, causing it to move. This motion of the receiver diaphragm will react upon the transmitter diaphragm; and consequently, if conditions are just right, there will be set up a vi

METHOD OF VENTILATING a Barn.

the roof. Screen openings should be provided on all sides. Slide shutters should be used for the interior openings.

Pipes over Batteries

Why should no metal pipes be run above a storage battery?-F. H. T.

If metal pipes are placed above a storage battery, the fumes arising from the solution come in contact with the metal. A speedy corrosion of the pipes naturally follows. Metal salts are formed in little scales, which jarring is likely to shake loose; and these, falling into the storage. cells, cause a very rapid deterioration of the plates. If, owing to the fact that pipes already have been installed, it is inconvenient to dispense with them, they may

be boxed in. It is better, however, to run the pipes around instead of over the batteries. In boxing-in the pipes, a black asphalt paint should be used on the wood, as asphalt is immune to the vapors.

A Geometrical Theorem

If two equal adjacent dihedral angles are cut by any plane (not perpendicular to the common edge of the dihedral angles), the angles formed

Since PQ is perpendicular to angle A, angle HOP is a right angle. Likewise PRK is a right angle. But angle HPQ = angle RPK, and PQ=PR. Then triangle HQP=triangle KPR, and HP = PK, and HQ = RK. Again, we saw that angle HPS = angle KPS. Then triangle HPS triangle KPS, having two sides and the included angle of one equal to two sides and the included angle of the other. Therefore angle PSH = angle PSK, being homologous angles of equal triangles.

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in that plane by the intersection of that plane with the faces of the dihedral angles, are equal. Please prove.-J. W. P.

If the cutting plane is passed through a line which is perpendicular to the edge of the dihedral angle, the problem admits of solution as follows:

Let PS be a line perpendicular to the edge AB. Pass the plane CPSD through PS, cutting LA in CS, and AM in SD.

Pass the plane TPR through PS perpendicular to AB. Drop the perpendiculars PQ and PR to the planes LA and AM. Then PQ will equal PR. (All points in the plane which bisects a dihedral angle are equally distant from the faces.) The angle PSQ = angle PSR, these being the plane angles of equal dihedral angles. PS = PS. The triangle PQS, having the hypothenuse and acute angle in each equal, triangle PSR; and QS=SR, being homologous sides, cutting CS in H, and SD in K, an forming the trihedral angles P-HQS and P-SRK. Dihedral angle H-SP

=

:

Q = dihedral ngle R-SP-K, being vertical dihedral angles.

Dihedral angle S-PQ-H = dihedral angle K-RP-S, being right dihedral angles.

The angle QPS = angle SPR because of equality of triangles QPS and PSR. Trihedral angle P-HQS trihedral angle P-SRK, having two dihedral angles and the included face angle of one equal to two dihedral angles and the included face angle of the other.

Then angle HPQ = angle RPK, and angle HPS = angle SPK, being homologous face angles of equal trihedral angles.

For Leaking Roofs

Will you please tell me how to construct a water spreader for roofs, so that water will not be concentrated at one point and leak through?-P. L. K.

We presume that the roof is of but slight pitch, as where the pitch is steep, and good slate or good shingles are used, a water spreader will not be necessary. The illustration shows the finished spreader in place. It should be made of copper or galvanized iron bent to the shape desired on any brake or bending machine. The width and length, of course, will be governed by conditions.

WATER SPREADER FOR Roof Top.

The particular design here pictured spreads the water out in a thin sheet; moreover, it cannot suffer injury by ice forming on it. The dimensions of the spreader should be about 18 by 15 inches. A little device of this sort will remedy the evil resulting from water working its way through the joints of shingles and boards. The value of an aid of this sort depends, of course, upon proper construction and placing.

Making a Post Auger

How would you make an auger for boring small post-holes, say three inches in diameter? Lumber is scarce and dear where I live.-B. N. A.

POST-HOLE AUGER.

Take a piece of soft steel, 3 inches by 1/4 inch, and 31⁄2 inches long, for the auger. Cut it as shown in the drawing, and sharpen the wing X, but not attempting to finish the spur. Then take a piece of round stock some 30 inches in length and a quarter of an inch through, and forge a handle hole in one end. Weld this piece to the auger blade and heat the latter, twisting it, to the left, in a vise. Finish up the cutting edges and make the spur a square point. The auger is then ready for use.

Disinfecting Water

Will disinfecting bad cistern water render it safe to drink? E. J. O.

The idea of adding chemicals, particularly those of a dangerous character, to water used for drinking purposes, has in the past been condemned. Sanitary engineers to-day, however, believe that such means of purification has a future. Alum in connection with mechanical filtration has been tried with success in many

cities. A particularly effective method, in which sulphates of iron, lime, and copper are used, has recently been developed, and was fully described in the TECHNICAL WORLD MAGAZINE for April, 1906. Ozone also has been employed with very satisfactory results. The mere mixing of the chemical with the water, however, will not produce the result desired. The work of disinfecting water should be done only by sanitary engineers or other qualified persons who understand the effects of chemicals and the methods of their use. Filtration and boiling are still the best methods for those using water in small quantities.

Patching Tire Shoe

What is the best method of treating the punctured shoe of an automobile tire?-E. A. H.

The object of treating is to prevent the inner tube from blowing through, and to keep out water and gravel. A small puncture may be covered with a piece of canvas saturated with some adhesive solution. For a cut more than an inch long, however, this simple remedy will not suffice. Two thicknesses of canvas, or even a special cover plaster, must then be employed. This covering should go. clear across the inside of the shoe and fold over the clinches.

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An attempt should not be made by other than the makers to repair permanently a deep cut. A temporary repair by means of a rawhide patch cemented to the interior, or a cover plaster, with a leather strap wound about the tire, may be effected.

A rawhide sleeve is better than a strap. It should be put in place as shown in the drawing. The sleeve should be plugged at the ends to prevent the entrance of dirt and water. Such a repair may last for a run of some 200 miles.

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DEVICE FOR SPRAYING AND WASHING PHOTOGRAPHIC NEGATIVES AHD PRINTS.

cure a small nozzle, such as is ordinarily found on an oil-can, and a long piece of rubber tubing. Attach one end of the tubing to the nozzle, and the other end to a small tank at a fair elevation above the plane on which the washing is to be done. Wash the plates or prints, and then spray them. The prints should not be held in the hand, as may the plates, but set on a pane of glass and frequently turned. This process will remove all traces of hypo in from eight to twelve minutes. If the stream is too strong, however, blisters will rise. Finally, the plates or prints should be allowed to soak for a few minutes before drying.

Checking Nuts

I find the use of the split pin for checking nuts unsatisfactory, as it is often difficult to replace, and, moreover, the nut loosens. Could you recommend a substitute?-A. T. K.

The split pin has its advantages, and, if properly placed, should give good service. Fig. 1, as indicated at a, shows the tendency of the nut to loosen till it forces itself against the pin. This is because the hole is not drilled in the right place. This difficulty may be obviated, however, by means of a washer, tightly fitted between pin and nut. Fig. 2 shows the correct way of driving the pin.

The taper pin is an excellent substitute for the split kind. Fig. 3 shows one inethod of placing it. There is a belief

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