MISCELLANEOUS APPARATUS
The field of applied electricity is such a wide one as to preclude any
exhaustive handling of the subject in a book of this size. The aim has
been to acquaint the young student with the basic principles of the
science, and it is his part to develop these principles along the lines
indicated in the preceding pages. But there are some practical
applications that may be properly grouped under the heading of this
chapter. They may serve as a stimulus to the inventive faculties of the
youthful experimenter, and since the pieces of apparatus now to be
described are useful in themselves, the time spent in their construction
will not be wasted.
A Rotary Glass-cutter
When making a circle of glass it is generally best to let a glazier cut
the disk, otherwise many panes are likely to get broken before the young
workman succeeds in getting out a perfect one. But with a rotary
glass-cutter the task is a comparatively simple one, and the tool is
really an indispensable piece of apparatus in every electrician’s kit.
(See Figs. 1 and 2.)
The wooden form is turned from pine or white-wood, and is three inches
in diameter at the large end, or bottom, one inch in diameter at the
top, and two inches high. It is covered with felt held on with glue.
Directly in the middle of the top a small hole is bored one-eighth of an
inch in diameter, and in this aperture an awl or marker is placed,
handle up, as shown in Fig. 2. Notice that the awl is not made fast to
the form, but is removable at pleasure. A hard brass strip twelve inches
long, five-eighths of an inch wide, and one-eighth of an inch thick is
cut at the end to receive a steel-wheel glass-cutter, as shown at the
foot of Fig. 1.
A number of one-eighth-inch holes are bored along the strip, and half an
inch apart, measuring from centre to centre. To cut a disk of glass the
form is placed at the centre of the pane, the latter being imposed on a
smooth table-top over a piece of cloth. The strip, or arm, is laid on
the form, and over a small washer, so that one of the holes lines with
that in the form. The awl is passed down through the strip and into the
block, and the cutter is arranged in the slot at the end of the arm.
Press down lightly on the handle of the awl, to keep the form from
slipping; then the cutter is drawn around the glass, describing the
circle, and cutting the surface of the glass, as shown by the solid line
in Fig. 4. The disk must not be removed from the pane until the margin
is broken away. With a straight-edge and a cutter score the glass across
the corners, as indicated by the dotted lines in Fig. 4; then tap the
glass at the underside along the line and break off the corners. After
the corners have been removed tap the glass again, following the line of
the circle; then break away the remaining fragments and smooth the
edge.
[Illustration: FIG. 1
FIG. 2
FIG. 3
FIG. 4
FIG. 5
FIG. 6
GLASS-CUTTING APPLIANCES]
To Smooth Glass Edges
To smooth the rough edge of glass there are several methods. The
simplest way is to hold the disk or straight-edge against a fine
grindstone and use plenty of water. The glass must be held edgewise, as
shown in Fig. 5, and _not_ flatwise, as shown in Fig. 6. To properly
grind a disk two workmen are necessary, one to turn the stone, and the
other to hold the disk by spreading the hands and grasping it at the
middle on both sides (see Fig. 5). In this manner the glass may be held
securely, and slowly turned, so that an even surface will be ground.
When the flat edge is smoothed, tilt the glass first to one side and
then the other, and grind off the sharp edges.
Another method is to lay the glass on a table, upon a piece of felt or
cloth, and allow the edge to project over the table for two or three
inches. Hold the glass down with one hand to prevent its slipping; then,
with a piece of corundum, or a rough whetstone and glycerine, work down
the edge until it is smooth, turning the glass continually so that the
edge you are working on hangs over the table. This process of grinding
is somewhat tedious, but perseverance and patience will win out.
To Cut Holes in Glass
Holes may be cut in glass in several ways by an expert, but the boy who
is a novice in this line should stick to slow and sure methods and take
no chances. Fortunately, glass is little used in voltaic electricity,
but it is indispensable in the construction of the frictional machines,
Leyden-jars, and condensers, where glass is used as the dielectric, also
for the covering-plates to instruments.
The simplest method is that of rotating a copper tube forward and
backward over the glass, using fine emery dust for the cutting medium
and oil of turpentine as a lubricant. The copper tube must be held in a
rack, so that its location will not shift during the rotating or cutting
motion. The rack in which the tube is held may be of any size, but to
take a disk or square of glass, twenty inches across, the frame should
be twenty-two inches long, ten inches wide, and twelve inches high, as
shown in Fig. 3.
The side-plates are eleven inches high and ten inches wide, the top is
twenty-two inches long and ten inches wide, while the under ledge is
twenty and a quarter inches long by ten inches wide. This frame is put
together with glue and screws. Across the back, from the corners down to
the middle of the under ledge, battens or braces are made fast to
prevent the frame from racking. A hole is made through the middle of the
top and under ledge for the copper tube to pass through. If
different-sized tubes are to be used, blocks to fit the top and under
board are to be cut and bored, so that they may be held in place with
screws when in use. To cut a hole in glass, place the disk or pane on a
felt or cloth-covered table, and over it arrange the frame, so that the
tube will rest on the spot to be drilled. Drop the copper tube down
through the hole, having first spread the bottom of the tube slightly,
so that it will not split the glass. Now put some emery inside the tube
so that it will fall on the glass; then place a wooden plug in the top
of the tube and arrange an awl, or hand-plate, so that the tube may be
pressed down. Take one turn about the tube with a linen line, or
gut-thong, and make the ends fast to a bow, so that it will draw the
string taut but not too tight. Lubricate the foot of the tube with oil
of turpentine, and draw the bow back and forth. At first the motion will
cause the copper to scratch the glass, and then cut it, until finally a
perfectly drilled hole is formed. During the operation both glass and
frame must be held securely, and the bow drawn evenly and without any
jerking motion. Holes of different sizes may be cut with tubes of
various diameters. Small holes may be cut with a highly tempered
steel-drill and glycerine, the drill being held in a hand-drilling tool
or in a brace.
Anti-hum Device for Metallic Lines
In overhead wires, where galvanized or hard copper wire is used, the hum
due to the tension of the wires, and the wind blowing through them,
causes a musical vibration which becomes most annoying at times. This
can be overcome by a simple device known as an “anti-hum.” It consists
of a knob made of wood or rubber, through which a hole is bored, and
around which a groove is cut. One end of the wire is passed through the
hole and a loop formed, the loose end being wrapped about the incoming
wire. The other end of the line is passed around the knob in the groove,
and the end twisted about the line-wire. The knob is then an insulator
and a sound-deadener at the same time. To complete the metallic circuit
a loop of wire is passed under the knob, the ends of which are made fast
to the line-wires, as shown at Fig. 7.
[Illustration: FIG. 7]
[Illustration: FIG. 8]
A Reel-car for Wire
It is not always convenient nor possible to carry about a heavy roll of
wire when hanging a line, especially if it is No. 12 galvanized wire, of
which there are from fifty to a hundred pounds in one roll. Wire should
be unwound as it is paid out, and not slipped off from the coil, since
it is liable to kink; therefore, some portable means of transporting it
should be provided. Line-wires over long distances are paid out from a
reel-truck drawn by horses. For the use of the amateur electrician the
reel-car shown in Fig. 8 should meet all requirements.
The reel is made from two six-inch boards, a barrel-head or a round
platform of boards, four trunk-rollers, and a bolt. From a six-inch
board cut two pieces five feet long. Eighteen inches from either end cut
one edge away so as to form handles, as shown at C C C C in Fig. 8,
rounding the upper and under edges to take off the sharp corners. Cut
four cross-pieces sixteen inches long; and from two-by-four-inch spruce
joist cut four legs twelve inches long, and plane the four sides.
Nail two of the cross-pieces to the legs; then nail on the side-boards
and so form the frame of the reel. Bore a half-inch hole through a piece
of joist; then nail it between the remaining two cross-boards, taking
care to get it in the centre, as shown at A. Arrange these pieces at the
middle of the frame, making them fast with nails driven through the
side-boards and into the ends of these cross-pieces. Drive some pieces
of matched boards together, and with a string, a nail, and a pencil
describe a circle twenty inches in diameter. With a compass-saw cut the
boards on the line, and join them with four battens made fast at the
underside with nails. Do not make the battens so that they will extend
out to the edge of the circle, but keep them in an inch or two, so that
the under edge of the turn-table will rest on four trunk-rollers screwed
fast to the top edges of the side-boards and end cross-pieces, as shown
at B. A half-inch bolt is passed down through a hole made at the middle
of the table, and through the block. Between the block and the underside
of the table several large iron washers should be placed on the bolt,
so that they will keep the table slightly above the rollers, the main
weight of the table and its load of wire being held by the middle
cross-brace. The object of the trunk-rollers is to relieve the side
strain on the bolt, and also to prevent friction between the edge of the
table and the frame, in case the tension on the wire pulls it to one
side. Bore six holes in the table, on a circle of twelve inches, and
drive hard-wood pegs in them, as shown in Fig. 8. When a roll of wire is
lying on the table two boys can easily lift and carry the car, and as
they do so the wire will pay out. Give all the wood-work a coat of
dark-green paint, and oil the trunk-rollers and the wood where the bolt
passes through. A pair of nuts should be placed on the lower end of the
bolt and a washer under its head. These lock-nuts must be screwed on
with two monkey-wrenches, forced in opposite directions, so that one nut
will be driven tightly against the other. This is to prevent the turning
of the table from unscrewing the nuts.
Insulators
For telegraph and telephone lines, where pole, tree, or building
attachments are necessary, insulators must be used to carry the wires
without loss of current. The regular glass, porcelain, or hard rubber
insulators, made for pole and bracket use, are of course the best. They
can be purchased at any supply-house for a few cents each, but there are
other devices which will answer equally well and which will cost little
or nothing.
Obtain some bottles of stout glass, the green or dark glass being the
toughest; then carefully break the bottle part away. In doing this hold
the bottle by the neck, with a piece of old cloth wrapped about it, to
prevent the glass chips from flying. Save all of the neck and part of
the shoulder, as shown in Fig. 9, so that the wire and its anchoring
loop will not slip off and fall down on the peg or cross-tree.
Hard-wood pegs cut from sticks one inch and a half square should be
whittled down so that they will fit in the neck and come up to the top.
The pegs should be long enough at the bottom to permit of their being
fastened to the supporting poles, trees, or building. In Fig. 10 three
ways of attaching insulators are shown. At A the peg is nailed to the
top of a pole, or a hole is bored in the pole and the peg driven down in
it. At B two sticks with peg ends are nailed to a pole in the form of a
[V], and across the sticks a cross-brace is made fast to prevent the
sticks from spreading or dropping down. This cross-brace is made fast to
both the sticks and the pole so as to form a rigid triangle. At C the
usual form of cross-tree, or [T] brace, is shown. The pegs may be nailed
to the face of the cross-plate, or holes may be bored in the top and the
pegs driven down into them. If the cross-piece is more than two feet
long, bracket-iron should be screwed fast to the pole and brace at both
sides, as shown at C. Where a cross-plate is made fast to a pole, a lap
should be cut out so that the plate can lie against a flat surface
rather than on a round one (see D in Fig. 10).
The shoulder of the bottle-necks must not rest on a cross-piece, or
touch anything that would lead to the ground or to other wires. The
shoulder acts as a collar, and so sheds water that in wet weather the
current cannot be grounded through the rain. The underside of the collar
should always be dry, and also that part of the peg protected by the
collar, thereby insuring against the loss of current. The relative
position of insulator and peg is shown at Fig. 9, and if the pegs are
cut carefully the bottle-necks should fit them accurately.
Joints and Splices
It is essential in electrical work to have joints, splices, unions, and
contacts made perfectly tight, so that the current will flow through
them uninterruptedly. A poor contact or weak joint may throw a whole
system out of order. For this reason all joints should be soldered
wherever practicable. In line work, however, this is impossible, except
where trolley-wires are joined, and these are brazed in the open air by
an apparatus especially designed for the purpose. In telegraph and
telephone lines perfect contact is absolutely necessary, and where
attachments are made to insulators the main-line should never be turned
around the insulator. The wire is brought up against the insulator, and
with a [U] wire the main-line is tightly bound to it, as shown at Fig.
11. If it is necessary to bind the main-line more securely to the
insulator, one or two turns may be taken around the insulator with the
[U] or anchoring wire; then with a pair of plyers a tight wrap is made.
When joining two ends of wire together, never make loops as shown in
Fig. 12 A. This construction gives poor contact, for the wire loops
will wear and finally break apart. Moreover, the rust that forms between
the loops will often cause an open circuit and one difficult to locate.
Care must be taken to make all splices secure and with perfect contact
of wires, and the only manner in which this can be done is to pass the
ends of wires together for three or four inches, as shown in Fig. 12 B.
[Illustration: FIG. 9]
[Illustration: FIG. 10]
[Illustration: FIG. 11]
[Illustration: FIG. 12]
[Illustration: FIG. 13]
Grasp one wire with a pair of plyers, and with the fingers start the
coil or twist, then with another pair of plyers finish the wrapping
evenly and snugly. Treat the other end in a similar manner, and as a
result you will have the splice pictured in Fig. 12 B, the many wraps
insuring perfect contact. This same method is to be employed for inside
wires, and after the wrap is made heat the joint and touch it with
soldering solution. The solder will run in between the coils and
permanently unite the joint. The bare wires should then be covered with
adhesive tape.
Avoid sharp turns and angles in lines, and where it is not possible to
arrange them otherwise it would be well to put in a curved loop, as
shown at Fig. 13. A represents a pole, B B the line, and C the
quarter-circular loop let in to avoid the sharp turn about the
insulator. The current will pass around the angle as well as through the
loop, but a galvanometer test would show that the greater current passed
through the loop and avoided the sharp turn.
“Grounds”
[Illustration: FIG. 14]
[Illustration: FIG. 15]
[Illustration: FIG. 16]
In the chapter on wireless telegraphy several good “grounds” were
described, any one of which would be admirably adapted to telegraph or
telephone circuits. In Figs. 14, 15, and 16 are illustrated three other
“grounds” that can easily be made from inexpensive material. The first
one, Fig. 14, is an ordinary tin pan with the wire soldered to the
middle of the bottom. The wire must be soldered to be of use, as the pan
would soon rust around a simple hole and make the “ground” a
high-resistance one. If the pan is buried deep enough in the earth, and
bottom up, it will last for several years, or so long as the air does
not get at it to induce corrosion.
The star-shaped “ground” is cut from a piece of sheet zinc, copper, or
brass, and is about twelve inches in diameter. The wire is soldered to
the middle of it, and it is buried four feet deep, lying flat at the
bottom of the hole.
In Fig. 16 a pail or large tin can is shown with the wire passing down
through the interior and finally reaching the bottom, where it is
soldered fast. The can is filled with small chunks of carbon, or
charcoal, and some holes are punched around the outer edge and bottom to
let the water out. The can is then buried three or four feet in the
ground. Use nothing but copper wire for “grounds,” and it should be
heavy--nothing smaller than No. 14. The wire should be well insulated
down to and below the surface for a foot or two, so that perfect action
will take place and a complete “ground” secured.
The Edison Roach-killer
When Edison was a boy he invented the first electrocution apparatus on
record. At a certain station on the Grand Trunk Railroad, where Edison
was employed as a telegraph operator, the roaches were so thick that at
night they would crawl up the partition between the windows and reach
the ceiling, where they would go to sleep. During the day they were apt
to become dizzy, lose their footing, and drop down on the heads of the
operators. This did not suit young Edison, so he devised a scheme for
their destruction. While watching a piece of telegraph apparatus one
day, he saw a roach try to step from a bar charged with positive
electricity to one through which a negative current flowed. The insect’s
feet were moist and so made a connection between the two bars. As a
consequence a short-circuit of high tension passed through its body and
it dropped dead. This put an idea into Edison’s head, and the
electrocution apparatus was soon in working order. The “killer” was the
most simple device one could imagine, and was composed of two long,
narrow strips of heavy tin-foil pasted side by side on a smooth board,
with a space of one-eighth of an inch between them, as shown at Fig. 17.
To one strip a positive wire was connected, while to the other a
negative or ground was made fast. High-tension current, or that from an
induction-coil, was connected with the wires, and the resulting voltage
was strong enough to give one a severe shock if the fingers of one hand
were placed on one plate and those of the other hand on the other plate.
This device was arranged across the window-casing in the path the
roaches were accustomed to travel on their nightly trips up the side
wall. It was not long after dark before roach number one sauntered up
the wall, crossed the under strip, and stepped over on the upper one.
But he went no farther, and he, with many of his friends and relations,
were gathered up in a dust-pan the next morning and thrown into the
stove.
[Illustration: FIG. 17]
[Illustration: FIG. 18]
In electricity, as in many other things, simplicity is the key-note of
success; and from this little device to employ the alternating current
for ridding a house of an insect nuisance sprang the grim apparatus
known as the “death chair,” used in the execution of first-degree
criminals in the State of New York. Many people think the mechanism for
electrocution is a complicated one, but it is quite as simple as the
Edison roach-killer. One pole is placed at the head of the criminal and
the other at the feet, the latter being bound fast so that perfect
contact can be had. Then an alternating current of fifteen hundred to
two thousand volts is run through the body, and death is instantaneous
and void of pain.
An Electric Mouse-killer
A modification of the simple roach-killer was recently used by the
author in his laboratory to get rid of some troublesome mice. A piece of
board was cut twelve inches square, the edges being bevelled so that it
would be an easy matter for the mice to climb up on it. An inch-wide
circle of sheet brass was prepared measuring eleven inches outside
diameter and nine inches inside. Another circle was cut measuring eight
inches and a half outside and six inches inside diameter. Both circles
were attached to the board with copper tacks and polished as bright as
possible, the finished board appearing as shown in Fig. 18.
Wires were soldered to each strip, and these in turn were connected to a
high-tension current of several thousand volts. Crumbs and small pieces
of meat were placed on the board inside the circles, and the trap was
set in a convenient place on the floor of the laboratory.
The next morning several mice lay dead on the floor, but at some
distance from the board, and this seemed a little mysterious. The
following night the author worked late in the laboratory. After
finishing what he had on hand, he turned down the lights and sat down
and watched the trap. Presently Mr. Mouse appeared from somewhere. He
sniffed the air, then approached closer to the board, sniffed again,
and, evidently concluding that he was on the right trail, he climbed up
the side of the board and stood on the outer strip. He placed one
fore-foot on the inner strip, and, bang! up he went in the air, and
landed on the floor a foot or more away. His jump into space was due to
the electric action on his muscles, for the current literally tore his
nervous system into shreds.
Mr. Mouse lost a great many friends and relatives that season in the
same manner, and the apparatus is confidently recommended as a certain
and humane agent for the destruction of all small vermin.