The Boy Mechanic Part 116

3. This is so plainly ill.u.s.trated that it needs no explanation.

--Contributed by Herbert Hahn, Chicago.

** Sharpening Scissors [419]

When sharpening scissors on a grindstone it is very difficult to procure a straight edge. For those not having the facilities of a grinding arrangement a very handy device that will produce a straight and sharp edge can be easily constructed as follows:

Procure a block of wood, 1-1/2 in. long, 1 in. wide and 1/2 in.

thick, add saw a kerf square with the face of the block, as shown at A. Attach a piece

[Ill.u.s.tration: A Block of Wood Fitted with a Piece of Emery Cloth for Sharpening Scissors Correctly]

of fine emery cloth in the kerf, at B, with glue, taking care to have it flat on the sloping surface only and allowing no part of the cloth to turn the sharp corner and lie on the back side. Apply the block to the scissor blade as shown and draw it back and forth from one end to the other, being careful to keep the back side of the blade flat against the block. Without being familiar with scissors grinding, anyone can sharpen them correctly with this block.

--Contributed by Harriet Kerbaugh, Allentown, Pa.

** Counter Brush for a Shop [419]

A very serviceable brush for use around a shop can be made from a discarded or worn-out push broom as shown at A. Pull out the bristles from one-half of the brush and shape the wood of that end with a knife or

[Ill.u.s.tration: A Discarded Push Broom Shaped to Form a Brush for the Bench or Counter]

spokes have to the form of a handle, and the brush will be formed as shown at B.

--Contributed by James T. Gaffney, Chicago.

** A Curtain Roller [419]

Procure a window-shade roller, an umbrella rib and two strips of oilcloth, each 1 in. wide and 4 in. long. Cut the

[Ill.u.s.tration: The Curtain is Easily Attached to and Detached from the Roller for Cleaning]

roller off so that it will be 6 in. longer than the distance across the window, then cut a groove in it to insert the rib. Sew the pieces of oilcloth so that they will just fit over the ends of the roller. When this is done lay the curtain across the groove, then press the rib and curtain into the groove and push the oilcloth bands over the ends of the rib to keep it in place.

--Contributed by E. L. McFarlane, Nashwaakees, N. B.

** Shade-Holder Bracket for a Gas Jet [419]

An old umbrella rib makes a very effective shade-holder bracket for a gas jet. The ends of the rib are bent to fit around the pendant upright and the support end is shaped into a hook. It can be quickly applied or removed. The outer end is bent into a hook to

[Ill.u.s.tration: The Bracket for Holding the Shade is Made from an Old Umbrella Rib]

hold the shade. The rib can be cut to fit a pendant arm of any length.

--Contributed by Edward Keegstra, Paterson, N. J.

** To Longer Preserve Cut Flowers [419]

A good way to keep cut flowers fresh is to place a small amount of pure salt of sodium in the water. It is best to procure this salt at a drug store because commercial salt will cause the flowers to wither, due to the impurities in the soda. Call for pure sodium chloride.

** Gla.s.s Blowing and Forming [420]

Fortunate indeed is the boy who receives a stock of gla.s.s tubing, a Bunsen burner, a blowpipe, and some charcoal for a gift, for he has a great deal of fun in store for himself. Gla.s.s blowing is a useful art to understand, if the study of either chemistry or physics is to be taken up, because much apparatus can be made at home. And for itself alone, the forming of gla.s.s into various shapes has not only a good deal of pleasure in it, but it trains the hands and the eye.

Gla.s.s, ordinarily brittle and hard, becomes soft and pliable under heat. When subjected to the action of a flame until dull red, it bends as if made of putty; heated to a bright yellow, it is so soft that it may be blown, pulled, pushed or worked into any shape desired. Hence the necessity for a Bunsen burner, a device preferred to all others for this work, because it gives the hottest flame without soot or dirt. The Bunsen burner, as shown in Fig. 1, is attached to any gas bracket with a rubber tube, but the flame is blue, instead of yellow, as the burner introduces air at its base, which mixes with the gas and so produces an almost perfect combustion, instead of the partial combustion which results in the ordinary yellow flame. All gas stoves have Bunsen burners, and many oil stoves.

If gas is not available, an alcohol lamp with a large wick will do almost as well. The blowpipe, shown in Fig. 2, is merely a tube of bra.s.s with the smaller end at right angles to the pipe, and a fine tip to reduce the size of the blast, which is used to direct a small flame. Besides these tools, the gla.s.s worker will need some round sticks of charcoal, sharpened like a pencil, as shown in Fig. 3, a file, and several lengths of German gla.s.s tubing.

To bend a length of the tubing, let it be a.s.sumed for the purpose of making a syphon, it is only necessary to cork one end of the tube and heat it near the top of the Bunsen flame, turning the tubing constantly to make it heat evenly on all sides, until it is a dull red in color. It will then bend of its own weight if held in one hand, but to allow it to do so is to make a flat place in the bend. The heating should be continued until the red color is quite bright, when the open end of the tube is put in the mouth and a little pressure of air made in the tube by blowing. At the same time, the tube is bent, steadily but gently. The compressed air in the tube prevents it from collapsing during the process.

To make a bulb on the end of a tube, one end must be closed. This is easily done by heating as before, and then pulling the tube apart as shown in Fig. 4. The hot gla.s.s will draw, just like a piece of taffy, each end tapering to a point. This point on one length is successively heated and pressed toward and into the tube, by means of a piece of charcoal, until the end is not only closed, but as thick as the rest of the tube, as in Fig. 5. An inch or more is now heated white hot, the tube being turned continually to a.s.sure even heating and to prevent the hot end from bending down by its own weight. When very hot, a sudden puff into the open end of the tube will expand the hot gla.s.s into a bulb, as in Fig. 6. These can be made of considerable size, and, if not too thin, make very good flasks (Fig. 7) for physical experiments. The base of the bulb should be flattened by setting it, still hot, on a flat piece of charcoal, so that it will stand alone.

To weld two lengths of, gla.s.s tubing together, heat the end of a tube and insert the point of a piece of charcoal in the opening, and twirl it about until the end of the tube has a considerable flare. Do the same to the end of the other tube, which is to be joined to the first, and then, heating both to a dull red, let them touch and press lightly together as in Fig. 8. As soon as they are well in contact, heat the two joined flares together, very hot, and, pulling slightly, the flares will flatten out and the tube be perfectly joined. Tubes joined without previous flaring have a constricted diameter at the joint.

To make a T-joint in two pieces of tubing, it is necessary to make a hole in the side of one piece, as shown at A in Fig. 9. This is accomplished by the aid of the principle of physics that gases expand when heated. Both ends of the tube, which should be cold, are corked tightly. The whole is then gradually warmed by being held near the flame. When warm, a small flame is directed by the blowpipe from the Bunsen flame to a spot on one side of

[Ill.u.s.tration: Gla.s.s Blowing and Forming]

the closed tube. As it heats, the air within the tube expands and becomes compressed, and as soon as the hot spot on the side of the tube is soft enough, the confined air blows out, pushing the hot gla.s.s aside as it does so, leaving a small puncture. This is to be enlarged with pointed charcoal until it also flares as shown at B.

This flare is then connected to the flared end of a straight tube, C, and the T-joint, D, is complete.

Using the blowpipe is not difficult. The lips and cheeks should be puffed out with a mouthful of air, which is ample to blow a flame while the lungs are being refilled. In this way, it is possible to use the blowpipe steadily, and not intermittently, as is necessary if the lungs alone are the "bellows."

Small gla.s.s funnels, such as are used in many chemical operations, are made by first forming a bulb, then puncturing the bulb at the top, when hot, with a piece of charcoal, and smoothing down or flaring the edges. Very small and fine gla.s.s tubes, such as are used in experiments to demonstrate capillary attraction, water or other liquid rising in them when they are plunged into it, are made by heating as long a section of tubing as can be handled in the flame--2 in. will be found enough--and, when very hot, giving the ends a sudden vigorous pull apart. The tube pulls out and gets smaller and smaller as it does so, until at last it breaks. But the fine thread of gla.s.s so made is really a tube, and not a rod, as might be supposed. This can be demonstrated by blowing through it at a gas flame, or by immersing it in colored liquid. The solution will be seen to rise some distance within the tube, the amount depending on the diameter of the tube.

The file is for cutting the gla.s.s tubing into lengths convenient to handle. It should be a three-cornered file, of medium fineness, and is used simply to nick the gla.s.s at the place it is desired to cut it. The two thumbs are then placed beneath the tube, one on each side of the nick, and the tube bent, as if it were plastic, at the same time pulling the hands apart. The tube will break off squarely at the nick, without difficulty.

The entire outfit may be purchased from any dealer in chemical or physical apparatus, or any druggist will order it. Enough tubing to last many days, the Bunsen burner, blowpipe, file and charcoal should not exceed $2 in cost.

** Cadmium and Solder [421]

The addition of cadmium to soft solder composed of tin and lead, lowers its melting point and increases its strength.

** Telegraph Codes [422]

[Ill.u.s.tration: Telegraph Codes]