The Boy Mechanic Part 32

Silver nitrate............................100 gr.

Solution B: Distilled water.............................4 oz.

Caustic stick potash (pure by alcohol)....100 gr.

Solution C: Aqua Ammonia.

Solution D: Sugar loaf................................840 gr.

Nitric acid................................39 gr.

Alcohol (Pure).............................25 gr.

Mix solution D and make up to 25 fluid oz. with distilled water, pour into a bottle and carefully put away in a safe place for future use, as it works better when old:

Now take solution A and set aside in a small bottle one-tenth of it, and pour the rest into the empty dish; add the ammonia solution drop by drop; a dark brown precipitate will form and subside; stop adding ammonia solution as soon as the bath clears.

Then add solution B, then ammonia until bath is clear. Now add enough of the solution A, that was set aside, to bring the bath to a warm saffron color without destroying its transparency. Then add 1 oz. of solution D and stir until bath grows dark. Place the speculum, face down, in the bath and leave until the silver rises, then raise the speculum and rinse with distilled water. The small flat mirror may be silvered the same way. When dry, the silver film may be polished with a piece of chamois skin, touched with rouge, the polis.h.i.+ng being accomplished by means of a light spiral stroke.

Fig. 3 shows the position of the gla.s.ses in the tube, also how the rays R from a star are thrown to the eyepiece E in the side of the tube. Make the tube I of sheet iron, cover with paper and cloth, then paint to make a non-conductor of heat or cold. Make the mounting of good seasoned lumber.

Thus an excellent 6-in. telescope can be made at home, with an outlay of only a few dollars. My telescope is 64 in. long and cost me just $15, but I used all my spare time in one winter in making it. I first began studying the heavens through a spygla.s.s, but an instrument such as I desired would cost $200--more than I could afford. Then I made the one described, with which I discovered a new comet not before observed by astronomers.- John E. Mellish.

** How to Make "Freak" Photographs [110]

The "freak" pictures of well-known people which were used by some daily newspapers recently made everybody wonder how the distorted photographs were made. A writer in Camera Craft gives the secret, which proves to be easy of execution. The distortion is accomplished by the use of prisms, as follows: Secure from an optician or leaded-gla.s.s establishment, two gla.s.s prisms, slightly wider than the lens mount. The flatter they are the less they will distort. About 20. deg. is a satisfactory angle. Secure them as shown by the sectional sketch, using strawboard and black paper.

Then make a ring to fit over the lens mount and connect it with the prisms in such a way as to exclude all light from the camera except that which pa.s.ses through the face of the prisms. The inner surface of this hood must be

[Ill.u.s.tration: Arrangement of Prisms]

dull black. The paper which comes around plates answers nicely. If the ring which slips over the lens mount is lined with black velvet, it will exclude all light and hold firmly to the mount, Place over lens, stop down well after focusing, and proceed as for any picture.

** Another Electric Lock [110]

The details of the construction of an electrically operated lock are shown in the ill.u.s.tration. When the door is closed and the bolt A pushed into position,

[Ill.u.s.tration: Simple Electric Lock]

it automatically locks. To unlock, push the b.u.t.ton D, which act will cause the electromagnet to raise the latch C, when the bolt may be drawn and the door opened.

--Contributed by A. D. Zimmerman, Boody, Ill.

** How to Mix Plaster of Paris [110]

For the mixing of plaster of Paris for any purpose, add the plaster gradually to the water, instead of the contrary, says the Master Painter. Do not stir it, just sprinkle it in until you have a creamy ma.s.s without lumps. Equal parts of plaster and water is approximately the correct proportion. The addition of a little vinegar or glue water will r.e.t.a.r.d the setting of the plaster, but will not preserve its hardening. Marshmallow powder also r.e.t.a.r.ds the setting. In this way the plaster may be handled a long time without getting hard. If you wish the plaster to set extra hard, then add a little sulphate of potash, or powdered alum.

** Enlarging with a Hand Camera [111]

Everyone who owns a hand camera has some pictures he would like enlarged. It is not necessary to have a large camera to do this, as the process is exceedingly simple to make large pictures from small negatives with the same hand camera.

A room from which all light may be excluded and a window through which the light can enter without obstruction from trees or nearby buildings, with a shelf to hold the camera and a table with an upright drawing-board attached, complete the arrangement. The back is taken out of the camera and fitted close against the back of the shelf, which must be provided with a hole the same size and shape as the opening in the back of the camera. The negative used to make the enlarged print is placed in the shelf at A, Fig. 1.

The rays of the clear, un.o.bstructed light strike the mirror, B, and reflect through the negative, A, through the lens of the camera and on the board, as shown in Fig. 2. The window must be darkened all around the shelf.

After placing the negative and focusing the lens for a clear image on the board, the shutter is set and a bromide paper is placed on the board. The paper is exposed, developed and fixed by the directions that are enclosed in the package of bromide papers.

[Ill.u.s.tration: Making Large Pictures with a Small Camera]

** Positioning A Hanging Lamp [111]

Don't pull a lamp hung by flexible cord to one side with a wire and then fasten to a gas pipe. I have seen a wire become red hot in this manner. If the lamp hung by a cord must be pulled over, use a string.

A Curious Compressed Air Phenomenon [111]

Push a pin through an ordinary business card and place the card against one end of a spool with the pin inside the bore, as shown in the sketch. Then blow through the spool, and it will be found that the card will not be blown away, but will remain suspended without any visible support. This phenomenon is explained by the fact that the air radiates from the center at a velocity which is nearly constant, thereby producing a partial vacuum between the spool and the card. Can the reader devise a practical application of this contrivance?

[Ill.u.s.tration: Experiment with Spool and Card]

** Simple Switch for Reversing a Current [111]

Take two strips of copper or bra.s.s and fasten them together by means of gutta-percha (Fig. 1); also provide them with a handle.

Saw out a rectangular block about one and one-half times as long as the bra.s.s strips and fasten to it at each end two forked pieces of copper or bra.s.s, as in Fig. 2. Fasten on the switch lever, as at A and B, Fig. 2, so that it can rotate about these points.

Connect the wires as shown in Fig. 3. To reverse, throw

[Ill.u.s.tration: Simple Current-Reversing Switch]

the lever from one end of the block to the other.

--Contributed by R. L. Thomas, San Marcos, Tex.

** Novel Mousetrap [112]

A piece of an old bicycle tire and a gla.s.s fruit jar are the only materials required for making this trap. Push one end of the tire into the hole, making sure that there is a s.p.a.ce left at the end so that the mice can get in. Then

[Ill.u.s.tration: A Baitless Trap]

bend the other end down into a fruit jar or other gla.s.s jar. Bait may be placed in the jar if desired, although this is not necessary.

--Contributed by Geo. Go McVicker, North Bend, Neb.

** Polis.h.i.+ng Nickel [112]