The Boy Mechanic Part 44

The base, H, can be made of oak, stained and varnished. The bottom of the box, A, is covered with lampblack so as to readily absorb all heat that strikes the surface. The black should not be put on until just before you paint the supports, cover and rim of the box with gold or silver paint. Hold the bottom of the box to be blackened over a little burning cotton saturated with turpentine.

The scale on the gla.s.s can be etched with hydrofluoric acid, or made with a little black paint. The water can be put in with a medicine dropper. This instrument will measure the amount of heat given by a candle some 20 or 30 ft. away.

--Contributed by J. Thos. Rhamstine.

** Home-Made Battery Voltmeter [153]

Secure a piece of bra.s.s tube 3 in. long that has about 1/4-in.

hole. Put ends, A, 1-1/4 in. square and cut from heavy cardboard on this tube. Make a hole in the center of each cardboard just large enough to allow the bra.s.s tube to fit tight. Put on two or three layers of stout paper around the bra.s.s tube and between the cardboard ends. Wind evenly about 2 oz. of No. 26 cotton covered magnet wire on the paper between the ends and leave about 2 in. of wire on each end extending from the coil. Use a board 1/2- in.

thick, 3 in. wide and 6 in. long for the base and fasten the coil to it, as shown in Fig. 1. Bore holes for binding-posts, B, one on each side of the board, and connect the two wires from the coil to them. At the other end of the board and in the center drive a wire nail and attach a small spring, C, to it. The spring should be about 1 in. long. Take a small piece of soft iron, D, 1/2- in.

long and just large enough to slip freely through the bra.s.s

[Ill.u.s.tration: Battery Voltmeter Construction]

tube and solder a piece of copper wire to it; the other end of the copper wire being hooked to the spring, C. The copper wire must be just long enough to allow the piece of iron, D, to hang part way in the end of the coil and still hold the spring in place. A circular piece of cardboard, E, is slipped over the spring to where the spring joins the wire. This cardboard is to serve as the pointer. A piece of paper 1-1/2 in. wide and 2-1/2 in. long is glued to the board so that it will be directly under the cardboard pointer and fit snugly up against the top of the coil.

The paper can be calibrated by connecting one cell of battery to the binding-posts. The iron plunger, D, is drawn into the tube and consequently the pointer, E, is drawn nearer to the coil. Make a mark directly under the place where the pointer comes to rest. At the place mark the number of volts the cell reads when connected with a voltmeter. Do the same with two or three cells and mark down the result on the scale. By dividing off the s.p.a.ce between these marks you may be able to obtain a surprisingly correct reading when connected with the battery cells to be tested.

--Contributed by Edward M. Teasdale, Cuba, N. Y.

** How to Make a Folding Canvas Cot [154]

All the material required to make the cot as shown in Fig. 1 consists of wood 1-1/2 in. square of which two pieces are 6 ft.

long; two pieces 2 ft. 3 in. long; two pieces 2-1/2 ft. long; four pieces 1-1/2 ft. long; four hinges; some sheet metal and 2-1/4 yd.

of 8-oz. canvas.

Make a rectangle of the two long pieces and the two 2-ft. 3-in.

pieces of wood as shown in Fig. 2, nailing well the corners together and reinforcing with a strip of sheet metal as shown in Fig. 3. The four pieces 1-1/2 ft. long are used for the legs, and two of them are nailed to one of the pieces 2-1/2 ft. long, making a support as shown in Fig. 5.

Make two of these--one for each end.

[Ill.u.s.tration: Details of Canvas Cot Construction]

The hinges are attached as shown in Fig. 5 and the whole support is fastened just under the end pieces of the frame by hinges. Four pieces of sheet metal are cut as shown in Fig. 4 and fastened to the body of the frame with their lower ends hooking over pins driven in each leg at the proper place. The canvas is stretched as tight as possible over the two long side pieces and fastened on the outside edge of each piece with large headed tacks. The legs will fold up as shown by the dotted line and the cot can be stored in a small s.p.a.ce.

--Contributed by R. J. Smith, Milwaukee, Wis.

** How to Make a Small Geissler Tube [154]

At first this would seem to be a difficult piece of work, yet a good and beautiful Geissler tube can be made at home in the following manner:

Procure a gla.s.s tube about 3-1/2 ft. long having a hole through its center about 1/8 or 1/4 in. in diameter, about 1 in. of No. 30 platinum wire and enough mercury to fill the tube and a small bowl. About 1-1/2 lb. of mercury will be sufficient. The first thing to do is to seal 1/2 in. of platinum wire in one end of the tube. This is done by holding the end of the tube with the right hand and taking hold of the tube with the left hand about 4 in.

from the right hand. Hold the tube in a flame of a bunsen burner in such manner that the flame will strike the tube midway between the hands, as shown in Fig. 1, and keep turning the tube so as to get an even heat. When the gla.s.s becomes soft,

[Ill.u.s.tration: Construction of Geissler Tube]

remove the tube from the flame and quickly draw it out into a fine thread. Break this thread off about 1/8 in. from the long part of the tube and the end will appear as shown in Fig. 2. Take 1/2 in.

of the platinum wire and slip it through the fine hole made by breaking the gla.s.s thread so that one-half of the wire will be inside of the long tube. If the end of the tube is now placed in the flame of the burner, the gla.s.s will adhere to the platinum wire and the wire will thus be sealed in the tube. The finished end will appear as shown in Fig. 3. This tube as described will be 8 in. long, although nearly any size could be made in the same way.

Measure 8 in. from the sealed end and place the tube at that point in the flame, holding in the left hand. At the same time take the piece of gla.s.s that was broken off at the end in the first operation and hold it in the flame with the right hand. When both the tube and piece of gla.s.s are soft, touch the soft part of the tube with the end of the gla.s.s and draw the tube out into a point like that shown in Fig. 4. Break off the piece of gla.s.s, thus leaving a. small aperture in the long tube. Seal the remaining 1/2 in. of platinum in this aperture in the same manner as before being careful not to heat the tube too suddenly. The tube is now ready for filling and the upper part will appear as shown in Fig.

5.

The air is expelled from the tube by filling with mercury. This may be done by making a paper funnel and pouring the mercury slowly into the tube through the funnel. When the tube is filled to within 1/2 in. of the funnel remove the funnel and tap the side of the tube gently in order to remove any small air bubbles that may be clinging to the sides of the tube. The air bubbles will rise and come to the top. The tube now must be filled completely, expelling all the air. Place a finger over the end of the tube to keep the mercury in and invert the tube and set the end in the bowl of mercury. The mercury in the tube will sink until the level will be at about 30 in., leaving 8 in. of vacuum at the top. The next operation is to seal the tube at the half-way point between the lower platinum wire and the mercury level.

As the lower end of the tube must be kept at all times in the bowl of mercury until the tube is sealed, an a.s.sistant will be necessary for this last operation. Have the a.s.sistant hold the tube in the mercury at a slight angle, using care to always keep the lower end in the mercury, while you hold the burner in the left hand and allow the flame to strike the tube at the stated point. The part of the tube above this point will gradually bend over of its own weight as the gla.s.s softens. When it reaches the angle of about 60 deg., Fig. 6, take hold of the tube with the right hand still keeping the flame on the tube, and gradually draw the softened portion out until it separates from the main tube.

The tube is now finished and when the platinum wires are attached to the terminals of a spark coil a beautiful blue light will appear in the tube with a dark s.p.a.ce at the negative end or cathode.

--Contributed by David A. Keys, Toronto, Can.

** Loosening Rusted Nuts [155]

Nuts that are rusted fast can often be loosened by giving a hard turn in the tightening direction.

** Cleaning Greasy Stoves [155]

Greasy stoves may be cleaned with a strong solution of lye or soda.

** How to Make a Take-Down Background Frame [156]

Many amateur photographers who desire to do portrait work at home have left the subject alone for the want of a suitable background.

A frame such as is used by the professional is entirely out of the question in most homes, says a correspondent of Camera Craft. The frame as shown in the sketch was devised and its chief advantage lies in the fact that when not in use it can be compactly tied together and stored away in a closet.

Almost any wood may be used in constructing this frame, but yellow pine is the best, as it is easily obtained and at the same time very well suited for such work. All pieces are to be dressed on all sides.

Two upright pieces are cut from 3/4 in. material 2 in. wide and 5 ft. 9 in. long and two blocks are fastened on the ends of each that are to be used for the bottom, as shown in Fig. 1. These blocks are each 2 by 6-in. and 1/4 in. thick. The base is made from a piece 3/4 in. thick, 3 in. wide and 5 ft. 4 in. long. A crosspiece 3/4-in. thick, 3 in. wide and 12 in. long, cut in the shape shown in Fig. 2, is screwed on each end of the base with 3-in. wood screws, as shown in Fig. 3. Four blocks 1/4 in. thick, 1 in. wide and 3 in. long are nailed to the sides of the base piece parallel with and at a distance of 2 in. from the end of same. This forms a slot, Fig. 4, to receive the pieces nailed to the ends of the uprights. To secure a rigid frame it is essential that this, joint be accurately put together.

Procure a piece of thick tin or bra.s.s and make two pieces like the pattern shown in Fig. 5, with each projection 3-in. long. The width of the crosspiece is 1 in. and the single projection 3/4 in.

These are bent and nailed, one on each end of a piece of wood that is 1/4 in. thick, 1 in. wide and 5 ft. long, as in Fig. 6. These will form two pockets that will fit over the tops of the uprights.

The frame is put together as shown in Fig. 7. Any background that will hang straight without need of being stretched can be hung on this frame.

[Ill.u.s.tration: FIG.6 -- Details of Background Frame]

** Home-Made Kite Reel [156]

This kite reel is constructed from two old pulleys and a few pipe fittings. The large pulley is about 14 in. in diameter, on the face of which are riveted flat strips of iron with extending arms.

These arms are reinforced by riveting smaller pieces from one to the