Things To Make - Archibald Williams (the reader ebook .TXT) 📗

in the base to take an ordinary wood screw of good size, the surplus of which is cut off so as not to interfere with the lamp.

The Shutter.—The woodwork is so simple that nothing further need be said about it. The more difficult part of the business is the making of the shutter, which must be so constructed that it can be opened and closed rapidly by motions similar to those used in working the telegraph key described in a preceding chapter. Speed of working is obtained by dividing the shutter into two or three parts, each revolving on its own spindle, but all connected so as to act in perfect unison. The thinnest sheet brass or iron obtainable should be used, so that the tension of the spring used to close the shutter need not be great. Our illustration shows a two-part shutter, each half an inch wider than the hole in the front, and jointly a similar amount deeper. The upper half overlaps the lower, outside, by a quarter of an inch.

The spindles are two straight pieces of brass wire, revolving in sockets which are most easily made of notched pieces of wood (as shown in Fig. 189), with removable caps of strip tin. The lower spindle should be an inch longer than the width of the front, to allow for a cranked end, to which the closing spring will be attached.

Having cut out the halves of the shutter, solder the spindle wires to one edge of each on what will be the back side. The wires must be so arranged as to allow a quarter of an inch to project beyond the left edge of the front, as the opening mechanism is situated on this side as the most convenient for the operator.

Take a couple of metal discs, an inch or so in diameter, and bore a hole in each near the circumference to fit the ends of the pivots fairly tight. Three-eighths of an inch from this—centre to centre—bore and tap a hole for a small screw. The tapping should be done with a taper tap and carried just so far that the screw turns stiffly without danger of being broken off by the screw-driver.

Next find the correct positions of the parts of the shutter and the spindle sockets on the front of the holder, and mark them off carefully. Screw the wooden parts of the sockets to the front. Four little "distance pieces" should now be cut out of small tubing, or made by twisting tin round the spindle, to place on the spindles between shutter and sockets, so that the shutters cannot shift sideways.

The right-hand end of the lower spindle must be bent over (after slipping on the distance piece) to form a 1/2-inch crank making an angle of 45 degrees with the line of the front, in an upward direction, as it will be depressed by the opening of the shutter. Flatten out the end with a hammer, and drill a small hole near the tip.

The shutters can now be placed in position, and the caps of the sockets be screwed on. The next thing to make is the connecting rod to join the cranks at the left side of the front. For this purpose we may use a piece of fairly stiff strip metal—brass by preference—5 or 6 inches long. Half an inch from one end make a mark with the centre punch; then measure off exactly the distance between the shutter spindles, and make a second punch mark. Drill holes at the marks large enough, for the disc screws to pass through easily, but not loosely.

Attach the rod to the discs by the screws, and slip the discs on to the ends of the shutter spindles. (The free end of the rod should be upwards.) Press the shutters against the front so that they cannot open, adjust the discs at an angle of 45 degrees to the front in an upward direction, and solder them firmly to the spindles.

The upper end of the connecting rod should be turned over to form a finger rest, or be sharpened off to take a knob. The last operation is the fitting of the spring to close the shutter. A spiral spring attached at one end of the crank on the lower spindle and at the other to a nail projecting from the side of the front is the most convenient arrangement. If you have not got a spiral spring, you can easily make a. fairly efficient substitute out of hard brass wire wound a few times round a large wire nail.

An alternative method of springing is to add an arm, a, to the connecting rod, as shown by dotted lines in Fig. 189, and to use the projection for engaging a spring, made by winding hard brass wire a few times round a nail. A screw passed through the coil holds it to the front.

The tension of the spring must be just sufficient to close the shutter smartly and prevent it rebounding far enough to pass any light.

XXXIX. A MINIATURE GASWORKS.

The most primitive method of making coal gas on a small scale is to fill a tin—which must have folded, not soldered, joints—with small coal, punch a hole in the bottom, and place it lid downwards in the fire. Gas soon begins to issue, but, owing to the quantity of moisture and impurities present, it will not ignite until some minutes have elapsed. The flame, when it does make its appearance, is very smoky and gives little light, because, in addition to the coal gas of commerce, there are present ammonia gas, sulphuretted hydrogen, carbonic acid, tar vapour, etc., which prevent brightness of flame.

[Illustration: FIG. 190.—General view of gas-making apparatus.]

A miniature gasworks, if it is to be worthy of its name, must obviously endeavour to separate the troublesome components from the useful gas. The doing of this involves several processes, all simple enough in principle, and requiring but simple apparatus for demonstration on a small scale. To take them in order the processes are—

(l) The formation of gas in a retort;

(2) The condensation of the tar;

(3) The condensation of steam;

(4) The removal of the ammonia gas;

(5) The removal of the sulphuretted hydrogen and carbonic acid.

The last two processes are, in a real gasworks, usually separated, but for simplicity's sake we will combine them. Finally, the storage of the gas has to be provided for.

The Retort.—To get very good results, the retort should be of cast iron, and have a removable air-tight cover; but, to keep down expense, we will use an ordinary 2-pound self-opening coffee tin. A short piece of brass pipe is soldered into the lid near one edge to carry off the gas as it is generated. To get a fairly gas-tight joint, red-leaded asbestos string should be rammed tightly between the lid and the tin. The tin may be laid on an open fire on the slant, the lid end uppermost, and the pipe at the top, where the gas will collect; or, if you wish to make things more realistic, you may easily construct an oven with sides and back of fire-brick, and front of sheet iron, through the hole in which the tin is pushed horizontally, so that only half an inch projects. This is a. suitable arrangement for out of doors.

[Illustration: FIG. 191.—Vertical section of condenser.]

The Hydraulic Main.—This is represented in Fig. 190 by a double-necked bottle, B, standing in a bowl of cold water. The pipe from the retort passes through the cork in one neck and dips half an inch below the surface of the water inside. The gas, on meeting the water, is cooled, and some of the steam in it is condensed, also most of the tar present, which floats on the top of the water. From the bottle the gas passes on to the Condensers, where the process of cooling is completed gradually. The condenser (Fig. 191) is so designed as to cause the gas to pass through several pipes in succession. The base consists of a tin box, 6 inches long, 4 wide, and 1-3/4 deep. This is divided longitudinally down the centre by a 1-1/2-inch partition, soldered to the bottom and sides; and the two divisions are again subdivided, as shown in Fig. 192, by shorter cross partitions.

[Illustration: FIG. 192.—Plan of condenser.]

For the condensing pipes, "compo" tubing of 1/2-inch outside diameter is convenient. The amount required will, of course, depend on the number of pipes used and the length of the individual pipes. The design shows 6 pipes, each 3 feet long, bent to a semicircular curve (Fig. 191) at the middle to form very long, narrow horse-shoes. The pipes are supported at the curve by the crossbar, S (Fig. 191), of a frame, and their ends enter short pieces of brass tubing soldered into holes in the bottom of the tin box. Rubber bands make the joints air-tight.

[Illustration: FIG. 193.—Vertical section of purifier.]

The base is stood bottom upwards in a larger tin containing an inch and a half of water. The water acts as a seal, preventing the passage of the gas from one compartment to another through the pipes which it traverses, in the order indicated by the arrows and numbers in Fig. 192, to reach the outlet. On its way the gas is deprived of any water and of any traces of tar. The condensed water and tar fall from the open ends of the pipes into the base.

The Purifier is made of a large tin with overlapping lid. Near the bottom is soldered on an inlet pipe; just below the lid an outlet pipe. Cut out two discs of perforated zinc or sheet tin to fit inside the tin easily, but not loosely. (If tin is used, make a number of small holes in it.) The lower of the discs (Fig. 193, Bl) has three wire legs, AA, soldered to it, to support the upper disc, B. Three short supports keep it clear of the bottom.

The tin must be charged with a mixture of two parts green sulphate of iron and one part lime. The lime should be slaked a short time before use. The sulphate, lime, and sufficient water to moisten the whole are ground into a pulp and left to dry. The dry mixture, which has a reddish-yellow colour, is broken up fine. Put tray B1 into place and spread half the chemical over it; then lay B on the top and cover it with the remainder. The lid joint is sealed by a broad rubber band.

While passing through the tin, the ammonia, sulphuretted hydrogen and carbonic acid gases all combine with the chemical, and fairly pure gas issues from the outlet.

The Gasholder.—As the gasometer is an important feature of a gasworks, our small plant should contain its counterpart, as it serves to regulate the pressure of the gas, and, therefore, the steadiness of the flame, as well as affording storage room.

As a gasometer, one may use a container made on the principle of the lung-testing apparatus described on p. 361; or the gasholder of a lantern acetylene apparatus, which must, of course, be suitably counterweighted.

Working the Plant.—When starting up the plant, leave the burner open until inflammable gas issues, so that the air present in the various chambers may be displaced.

[Transcribers note: Premature lighting of the burner may cause the flame to propagate into the system and explode. I speak from experience.]

INDEX.

Aeroplane, model, self-launching.
Bedplate for engine.
Bellows, double.
Bench, joiner's.
Benham's harmonograph.
Bicycle shed.
Boilers, model.
Bookstand.
Box kites.

Cabinets, cardboard, cigar-box, match-box, tool.
Circles, rolling.
Clock, electric alarm.
Colour top.
Cylinder, double-acting steam.

Developing sink.
Doors for shed.
Double-acting horizontal steam engine.
Double bellows.

Eccentrics.
Electric alarm clock.
Electric motor, reciprocating.
Electric railway.
Engine, hot-air.
Experiments, apparatus for simple scientific.

Fuels for model boilers.

Gasworks, miniature.
Ganges, rain, water,
Gimbals, or universal joints.
Gliders, paper.
Goold's harmonograph.
Governor for engine.

Harmonographs.
Hot-air engines.
House ladder.

Joiner's bench.

Kettles, quick-boiling.
Kites, box.
Kite winders.

Ladder, house.
Lamp, signalling.
Locomotive, electric.
Lung-testing apparatus.
Magic swingers.
windmill.
Match-boarding.
Match-box, self-supplying.
Morse code.
Morse sounder.
Motor, electric.
Motor, water.

Nozzle for steam turbine.

Pantograph.
Pendulums for harmonograph.
Pens for harmonograph.
Pneumatic puzzle.
Poultry house.
Propellers for aeroplane.
Pumps.
Puppets, wrestling.
Puzzle, pneumatic.

Railway, electric.
Rain gauges.
Reciprocating steam engine, simple.
Resistance, adjustable, for electric railway.
Reversing switch for electric railway.
Riveting.

Safety Valves.
Sawing trestle.
Shed for bicycle.
Signalling lamp.
Silhouette drawing machine.
Simple scientific experiments.
Sink, developing.
Slide valve.
Smoke-ring apparatus.
Soldering.
Spokes, magic.
Steam cocks.
Steam engines.
Steam gauge.
Steam pump.
Steam tops.
Steam turbines.
Strength. testing machines.
Swingers, magic.
Switch, multiple battery.
Switch, reversing.

Target apparatus.
Telegraphic apparatus.
Testing boilers.
Tool cabinet.
Top, colour.
Tops, steam.
Track for model railway.
Trestle, sawing.
Turbines, model steam.

Vanishing spiral.
Vice for Joiner's bench.

Water gauge.
Water motor.
Weights for harmonograph pendulums.
Windmill, magic.
Wind vanes; electric.
Workbox, Norwegian.
Wrestling puppets.
Wriggling line.

THE END. PRINTED IN GREAT BRITAIN AT THE PRESS OF THE PUBLISHERS.