(a) If the pendulums are working against each other—
antagonistically—there will be loops or points on the outside of the
figure equal in number to the sum of the figures in the ratio.
(b) If the pendulums are working with each other—concurrently—the loops
form inside the figure, and are equal in number to the difference
between the figures of the ratio. To take the 1:3 ratio as an example.
If the tracing has 3+1=4 loops on the outside, it is a specimen of
antagonistic rotation. If, on the other hand, there are 3-1=2 loops on
the inside, it is a case of concurrent rotation. (Fig. 176, A.)
2. Figures with a ratio of which the sum of the numbers composing it is
an even number (examples, 1:3, 3:5, 3:7) are symmetrical, one half of
the figure reproducing the other. If the sum is Uneven, as in 1:2, 2:3,
2:7, the figure is unsymmetrical. (Fig. 177, A.)
3. The ratio 1:3 is the easiest to begin upon, so the experimenter’s
first efforts may be directed to it. He should watch the growth of the
figure closely, and note whether the repeat line is made in front of or
behind the previous line of the same loop. In the first case the figure
is too flat, and the weight of the upper pendulum must be raised; in
the second case the weight must be lowered. Immediately an exact
harmonic is found, the position of the weight should be recorded.
Interesting effects are obtained by removing the lower pendulum and
allowing the apparatus to describe two elliptical figures successively,
one on the top of the other, on the same card. The crossing of the
lines gives a “watered silk” appearance to the design, which, if the
pen is a very fine one and the lines very close together, is in many
cases very beautiful.
Readers who wish for further information on this fascinating subject
are recommended to purchase “Harmonic Vibrations,” published by Messrs.
Newton and Co., 72 Wigmore Street, London, W. This book, to which I am
much indebted, contains, besides much practical instruction, a number
of charming reproductions of harmonograms.
Before closing this chapter I should like to acknowledge the kind
assistance given me by Mr. C. E. Benham, who has made a long and
careful study of the harmonograph.
XXXII.
A SELF-SUPPLYING MATCHBOX.
This useful little article can be constructed in a couple of hours by a
handy person. In general idea it consists of a diamond-shaped box to
hold vestas, working up and down diagonally on a vertical member (A in
Fig. 179 (1)), which passes through slits at the top and bottom, and
runs in grooves cut in the sides of the box. The top of A is grooved to
allow a match to rest on it. When the box is drawn up to the full
extent allowed by a transverse pin in the slot shown in Fig. 179 (2),
the groove is at the lowest point of the box, and is covered by the
matches. When the box is lowered, A catches a vesta and takes it up
through the top, as seen in Fig. 178, for removal by the fingers.
The only materials required are a cigar-box, some pins, and a supply of
glue. The box should be carefully taken to pieces, and the parts soaked
in hot water till freed of all paper, and then allowed to dry under
pressure, small slips of wood being interposed across the grain to keep
them separate and permit the passage of air.
[Illustration: FIG. 178.—Self-supplying matchbox, with match in
position for removal by fingers.]
When the wood is dry, cut out with a fret saw two pieces shaped like
Fig. 179 (3), to form the ends of the box. Allow a little surplus, so
that the edges may be finished off neatly with chisel and plane. The
two ends should match exactly, or there will be trouble at a later
stage.
Now cut, down the centre of each a groove for one edge of A to run in.
By preference it should be square; but if you do not possess the
necessary chisel, a V groove made with a knife will suffice—and, of
course, in this case the edges of A will have to be bevelled to fit.
[Illustration: FIG. 179.—Details of self suplying matchbox.]
The four sides of the box, BB and CC, are next cut out. Their sectional
shape is shown in Fig. 179 (1). They should be rather longer than the
length of the ordinary vesta, and all of exactly the same length, and
rectangular. A very small hack saw (costing about 1s.) with fine teeth
is the best possible tool for close cutting, and a small 1 shilling
iron plane is invaluable for truing and bevelling the edges.
The glue pot, which we will assume to be ready for use, is now needed
to attach the fixed B (the other B is hinged to form a lid for filling
the box through) and CC to the ends. This operation must be carried out
accurately, so that the slots may not be blocked.
While the glue is setting, cut out A, allowing an extra 1/16 inch of
width for fitting. The slot down the centre is best made with a fret
saw, and should be smoothed internally by drawing a strip of fine glass
paper to and fro through it. The length of the slot is of great
importance. It must reach to just that distance from the top edge which
brings that edge flush with the bottom of the box when the box is
raised; and in the other direction must permit the box to settle on to
its foot, so that the match lifted shall project above the box.
Work the edges of A down carefully (double-bevelling them if the
notches are V-shaped) till A will run easily, but not loosely, in the
box. Then cut out two slips, DD, and bevel them at the top to an angle
of 45 degrees. Put A in place and glue them on, taking care that the
glue does not hold them fast to A.
Pierce a small hole through DD, in line with the slot, and insert a
pin.
Draw the box fully up, and see if the top of A sinks to the proper
place.
If it projects a little, lengthen the slot a trifle.
Cut out the supports EE, finish them neatly, and glue them to A. Make
sure that the pin lets the box touch them.
Fix on the lid B with two pins for pivots, and fit a little catch made
of brass wire. To give extra security, drive ordinary pins, cut off to
5/8 inch, through the sides into fixed B, CC, and DD, and through EE
into A. This is an easy enough business if pilot holes are made with a
very fine awl or a tiny drill, and a small, light hammer is used. It
now remains only to go over the whole box with glass paper or emery
cloth, and to glue a diamond of coarse glass paper to one end for
striking the matches on.
Note that the lid must not be opened when the box is down, as it would
be wrenched off its pivots.
XXXIII.
A WOODEN WORKBOX.
The box illustrated by Fig. 181 was copied from an article of Norwegian
manufacture. Its construction is an extremely simple matter, provided
that one can get a piece of easily bent wood (birch, for instance), not
exceeding 3/16 inch in thickness, for the sides.
[Illustration: FIG. 180.—Showing how to draw an ellipse.]
[Illustration: FIG. 181.—Norwegian workbox.]
The bottom of the box is made of 5/16 or 3/8 inch wood, cut to an oval
or elliptical shape. To mark out an ellipse about 8 inches long and
5-1/2 inches wide—this will be a. convenient size—stick two pins into
the board 5-1/8 inches apart, pass a loop of thread 14 inches in
circumference round these, and run the point of a pencil round the pins
in the path which it has to take when confined by the slack of the loop
(Fig. 180). Fret-saw along the line.
The wood strip for the side is 4-1/2 inches deep, and 1-1/2 inches
longer than the circumference of the bottom. The ends are thinned off
somewhat, as shown in Fig. 181, to prevent the lap having a clumsy
appearance, and the surface is smoothed all over with sandpaper. Bore a
number of small nail holes 3/16 inch from one edge, and then steam the
wood over a big saucepan or other suitable vessel until it is quite
lissom.
When attaching the side piece to the bottom, begin at the middle, and
work first towards what will be the inside end of the lap, and then
towards the outside end. Nails are driven in through the holes already
drilled. When nailing is finished, clip the top of the overlap with a
hand-vice or screw spanner, to prevent the tops of the ends sliding
over one another, and bore a line of holes l/4 inch apart, and at the
same distance from the outer end. Fine copper wire drawn to and fro
through alternate holes from one end of the row to the other and back
again, will secure the joint.
The lid overlaps the side 1/4 inch in all directions and has a square
notch cut in it at one end to pass under the piece A, and at the other
a deeper, circular-ended nick to enable it to pass over the key B when
that is turned into the position shown in the illustration. A is cut
out of 1/4-inch wood; B, in one piece, out of 1/2-inch. Their length
under the heads exceeds the inside depth of the box by the thickness of
the lid.
A is affixed rigidly to the side by small screws or wire, while B must
be attached in a manner, which will allow the head to rotate. Cut two
nicks round the shank, and two horizontal slots at the same height
through the end of the box. A couple of brass rings must then be
procured of such a size that, when flattened into a somewhat oval
shape, they will project beyond the slots sufficiently to allow a piece
of wire to pass through them and prevent their being drawn back again.
Quarter-inch wood will do for the lid. A handle is made out of a couple
of inches of small cane bent into a semicircle, let through the lid at
each end, glued, and cut off flush.
The exterior may be decorated by a design in poker-work, or be stained
and varnished. This is left to the maker’s discretion.
XXXIV.
WRESTLING PUPPETS.
[Illustration: FIG. 182.—Peg marked for cutting and drilling.]
The expenditure of a halfpenny, and a quarter of an hour’s use of a
pocket knife, bradawl, and pliers, will produce a toy which is
warranted to amuse grown-ups as well as children. Wrestlers made out of
clothes pegs may be bought for a copper or two in the street, and are
hardly a novelty; yet a few notes on home production will not be a
waste of space, as making is cheaper, and much more interesting, than
buying.
The clothes pegs used must be of the shape shown in Fig. 182, with a
round top. They cost one penny per dozen.
Drill holes through body and legs as indicated in Fig. 182. Cut the
legs from the “trunk,” and whittle them to the shape of Fig. 183. The
arms, made out of any thin wood, are 2-1/4 inches long between centres
of end holes.
To get the best results the two arms and the four legs should be paired
off to exactly the same length.
[Illustration: FIG. 183.—Clothes-peg wrestlers.]
The neatest method of attaching the parts is to use small brass tacks,
which must, of course, be of somewhat larger diameter than the holes in
the body. Holes in arms and legs are a loose fit, so that the wrestlers
may be very loose-jointed, and the tacks must not be driven in far
enough to cause any friction.
Instead of tacks one may use wire passed through the parts and secured
by a bend or loop at each end. Wire has the disadvantage of entangling
the thread which works the figures.
When assembling is finished, bore holes in the centres of the arm
pieces, pass a piece of wire through, and twist it into a neat loop at
each end. To one loop tie 2 feet of strong thread (carpet thread is
best), and to the free end of the thread a large nail or hook. The
other loop has 6 feet or so of thread tied to it, to be worked by the
hand. If the thread is stained black, it will be practically invisible
by artificial light.
The nail or hook is stuck under the edge of the carpet, or into some
crack or cranny which affords a good hold, and the wrestlers are worked
by motions of the hand. The funniest antics are produced by very slight
jerks.
If the arms are set too close together the heads may stick between
them, in which case one must either flatten off the sides of the heads
or insert fresh arm wires of greater length. If a head persists in
jamming against the thread wire or getting under it and staying there,
cut 1/2 inch off a pin and stick it into the front of the crown, so
that the head is arrested by the wire when the wrestler bends forward.
[Illustration: FIG. 184.—Large wrestlers made of stout wood.]
Large Wrestlers.—A more elaborate and realistic pair is shown in Fig.
184. The originals of the sketch are 8 inches high. Half-inch deal was
used for the bodies, 3/8-inch for the legs and arms. The painting-in of
hair, features, tights, and shoes adds considerably to the effect. The
heads and limbs are mere profiles, but anyone with a turn for carving
might spend a little time in rounding off and adding details which will
make the puppets appear more lifelike.
XXXV.
DOUBLE BELLOWS.
The small-sized bellows which have become popular in sitting-rooms are
usually more ornamental than efficient, and make one think regretfully
of the old-fashioned article of ample capacity which is seldom seen
nowadays.
Fig. 185 illustrates a method of coupling up two small bellows in such
a manner as to provide an almost continuous blast, besides doubling the
amount of air sent through the fire in a given time, at the coat of but
little extra exertion. A piece of wood half an inch thick is screwed
across one bellows just behind the valve hole. The two bellows are then
laid valve facing valve, and are attached to one another by a strip of
tin passed round the wood just behind the nozzles and by tying the two
fixed handles together.
[Illustration: FIG. 185.—Double-acting bellows. Two methods of coupling
shown.]
Make a rectangle of stout wire somewhat wider than the handles and long
enough to reach from the outer face of one moving handle to that of the
other, when one bellows is quite closed and the other full open. The
ends of the wire should be soldered together, and the ends of the link
held up to the handles by a couple of staples.
An alternative method is to use a piece of wood with a screw driven
into it at right angles near each end through the staples on the
handles (Fig. 185, a). In place of the staples you may use screw-in
eyes fitting the screws.
XXXVI.
A HOME-MADE PANTOGRAPH.
The pantograph is a simple apparatus for copying drawings, maps,
designs, etc., on a reduced or enlarged scale, or to the same size as
the original.
[Illustration: FIG. 186.—Details of simple pantograph.]
A sketch of a pantograph is given in Fig. 186. Four rods are jointed
together to form a parallelogram, the sides of which can be lengthened
or shortened to suit the scale of reproduction. One is attached by a
fixed pivot at a to the board on which the drawing is done. At b and e
are removable pivots, used for adjusting the rods; at c is a pivot
which projects an inch or so below the rods. The pointer is inserted at
d for enlargement, or at f for reduction, the pencil being in the
unoccupied hole at d or f.
If a same-sized copy is desired, the fixed pivot is transferred to d,
and the pencil and pointer placed at a and f respectively.
Construction of an Enlarging and Reducing Pantograph.—Cut out of
1/8-inch oak, walnut, or beech four rods 5/8 inch wide and 19 inches
long. Smooth them well all over, and make marks near the ends of each,
exactly 18 inches apart. The graduation of the rods for the adjustment
pivot holes is carried out in accordance with the measurements given in
Fig. 187. It is advisable to mark out and bore each rod separately if
you do not possess a machine which will drill holes quite
perpendicularly; if you do, all four rods can be drilled at one
operation.
In Fig. 187 the lower row of numerals indicates the number of times (in
diameters) the original is enlarged when all four holes similarly
figured are used; the upper row, the size of the copy as compared with
the original in case of reduction.
If proportions other than those given are required, a very little
calculation will locate the necessary holes.
Pivots.—All the pivots must fit their holes accurately, as any
looseness at the joints detracts from the truth of reproduction. For
pivots band b and e may use brass screws and small pieces of hard wood
as nuts to hold them in position. The nuts should screw on rather
stiffly, and not be forced hard against the rods, as free motion with
little friction at all joints is essential for good work.
[Illustration: FIG. 187.—Diagram showing how to mark off pantograph
rods. The dotted lines above rod give distances of holes from ends.]
The fixed pivot at a may be merely the shank of a wire nail of the
proper size driven into the board, a cork collar being slipped over it
to keep the rod the proper distance from the board. For c use a screw
to the head of which has been soldered half an inch of a round-headed
brass nail, which will move easily over the paper. At d is needed a
hollow pivot, fashioned out of a quarter of an inch of pencil-point
protector or some other thin tube, burred over slightly at the ends so
as not to fall out. The end of B at f has a slotted hole to grip the
pencil or pointer, as the case may be.
A Same-size Pantograph.—For making a same-size copy, tracing may be
preferred to the use of a pantograph; but if a pantograph is adopted, a
special apparatus may be constructed for the purpose. The arrangement
is exactly the same as that already described, excepting that the only
holes needed are those at a, c, d, f, at the middle points of the four
rods, the parallelogram formed by the rods being equal-sided. The fixed
pivot is situated at d, and pencil and pointer holes are made at a and
f.
Using the Pantograph.—When adjusting the instrument for reduction or
enlargement, make sure that the adjustment pivots are in the holes
corresponding with the scale. The fixed pivot, pointer, and pencil must
be rigid, and, with pivot c, be of such a length that the pantograph as
a whole moves parallel to the paper. A little sliding weight to place
on the rod near the pencil will be found useful for keeping the pencil
point in constant contact with the paper.
If the apparatus works stiffly, ease the holes a trifle and lead-pencil
the wood at all points where two surfaces rub. It is absolutely
impossible to make a good reproduction with a stiff, jerky pantograph.
To decide the positions of original and the paper for the copy, get the
pointer centred on the original and adjust the paper till its centre is
under the pencil.
XXXVII.
A SILHOUETTE DRAWING MACHINE.
With this very simple apparatus you will be able to give good
entertainment to such of your friends as may wish to have black paper
records of their faces in profile.
The machine is merely a long rod, with a sliding pencil attached to one
end and a metal pointer stuck into the other, supported near the pencil
end on a pivot which permits free movement in all directions.
For heads and busts only, the rod and pointer combined need not be more
than 4 feet 6 inches long. The rod is a 1/2-inch blind rod, the pointer
a stout knitting-needle driven axially into one end of the rod. This
pointer, being of small diameter, follows the minor curves and angles
of the features much more closely than would be possible with the rod.
The support is a piece of wood, 1-1/2 inches square and 12 to 15 inches
long, screwed on to a large foot, which should be fairly heavy, as any
tilting or slipping will, of course, spoil the silhouette. The
universal joint for the rod is made by soldering a small U-shaped piece
of metal to the end of a short metal bar. The ends of the U are drilled
for a pin passing through the rod; and a hole is sunk into the top of
the support to take the bar. The fit should be close, to prevent the
pivot rocking about, and the hole in the support deep enough to bring
the bottom of the stirrup down against the wood.
If a series of holes half an inch apart is drilled, through the rod,
the nearest 9 inches from the pencil end, the size of the silhouette
proportionately to the original can be varied by moving the pin from
one hole to another.
[Illustration: FIG. 188.—Silhouettograph in use.]
[Illustration: FIG. 188a.—Group of silhouettes drawn with the machine
described.]
The pencil holder is 4 inches of tubing, in which the pencil can slide
easily without shaking. If necessary, the size of the pencil should be
reduced by rubbing with glass paper. Bind the holder tightly to the end
of the rod away from the pointer, so that one extremity just overhangs
the rod. A piece of thin elastic is tied to the unsharpened end of the
pencil and to the pencil tube, the adjustment allowing the pencil to
project an inch when the elastic is taut but not stretched.
A fairly soft pencil and a thick, smooth paper or card give the best
results. Paper should be backed by something hard to prevent the pencil
digging in. Attach the paper to a firm vertical surface, such as the
side of a box, a drawing board, a wall, etc.
Using the Machine.—The rod support, paper, and sitter should be
arranged so that the rod is level at the height of the sitter’s nose
and the pencil on the centre of the paper. Bring the support near
enough to the paper to drive the pencil back into the tube until the
point projects only half an inch.
A thread attached to the pencil will enable you to keep the pencil off
the paper until you wish to begin drawing the profile.
Begin with the pointer pressing against the sitter’s chest, and bring
it over the face and down the back of the head and neck. Do not press
it into the hair, but carry it along what you consider to be the
outline; though it must be in actual contact with the features and
clothes. It is hardly necessary to mention that the sitter must keep
perfectly still if the silhouette is to be at all accurate.
The tracing is cut round with fine-pointed scissors, and the paper
blacked and stuck on a piece of white card. Some trouble is saved by
using paper white on one aide and black on the other. If duplicates are
needed, two or more pieces of paper should be stuck together by the
corners and to the paper on which the silhouette is drawn, and all be
cut through at one operation.
With a little practice the actual tracing of the outline occupies but a
few seconds. Things are expedited if an assistant adjusts the paper and
pencil.
XXXVII.
A SIGNALLING LAMP.
Visual signalling is effected at night in the Morse code by means of a
lamp fitted with an easily-moved shutter, which passes or cuts off the
light at the will of the operator. Readers who know the Morse code
might well go to the trouble of constructing in duplicate the simple
apparatus to be described, as the possession of an outfit will enable
them to extend their signalling capabilities.
The stand for the lamp is admirably supplied by the ordinary camera
tripod.
For the illuminant we may select any good acetylene cycle lamp.
For this a holder is made of 1/2-inch wood, according to the sketch
shown in Fig. 189. The width of all the four parts should be about 2
inches greater than the front glass of the lamp. B and C should be
sufficiently far apart to allow the lamp to rest on the rim above the
carbide chamber; and the front, A, should be at least an inch higher
than the top of the lamp glass.
[Illustration: FIG. 189.—Signalling lamp with quick-moving shutter.]
The hole cut in B must be so situated as to bring the front of the lamp
close to the front of the holder, so that the greatest possible amount
of light may be utilized. The hole in A should be rather larger than
the lamp front, and, of course, be accurately centred. Mark these two
holes off carefully, and cut out with a pad saw or fret saw.
A socket must be attached to the centre of the underside of the base to
take the camera screw; or, if such a socket is not easily obtainable, a
hole should be drilled 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.]