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* * * * *
ELECTRIC BELLS AND
ALL ABOUT THEM.
A Practical Book for Practical Men.
_WITH MORE THAN 100 ILLUSTRATIONS._
BY
S. R. BOTTONE,
CERTIFICATED BY SOUTH KENSINGTON (LATE OF THE COLLEGIO
DEL CARMINE, TURIN, AND OF THE ISTITUTO
BELLINO, NOVARA);
_Author of "The Dynamo," "Electrical Instruments for
Amateurs," &c._
LONDON:
WHITTAKER & CO., PATERNOSTER SQUARE, E.C.
1889.
(_All rights reserved._)
PREFACE.
So rapidly has the use of electric bells and similiar signalling
appliances extended, in modern houses, offices, hotels, lifts, and
ships, that every bell-fitter must have felt the need of accurate
knowledge of the manner in which these instruments act and are made.
In the following pages the author has attempted to supply this need, by
giving full details as to the construction of batteries, bells, pushes,
detectors, etc., the mode of wiring, testing, connecting up, localizing
faults, and, in point of fact, by directing careful attention to every
case that can present itself to the electric-bell fitter.
CARSHALTON, SURREY,
_November, 1888_.
CONTENTS.
CHAP. PAGE
I. PRELIMINARY CONSIDERATIONS 1
II. ON THE CHOICE OF BATTERIES FOR ELECTRIC BELL WORK 18
III. ON ELECTRIC BELLS AND OTHER SIGNALLING APPLIANCES 59
IV. ON CONTACTS, PUSHES, SWITCHES, KEYS, ALARMS, AND RELAYS 109
V. ON WIRING, CONNECTING UP, AND LOCALISING FAULTS 144
LIST OF ILLUSTRATIONS.
FIG. PAGE
1. Direction of current in cell 9
2. " " out of cell 10
3. Bar and horse-shoe magnets 14
4. The Dynamo 16
5. " Smee cell 28
6. " Daniell cell 30
7. " Gravity cell 32
8. " Leclanch['e] cell and parts 34
9. " Agglomerate cell 40
10. " Judson cell 42
11. " Battery in box 43
12. " Gent cell 44
13. " Bichromate cell 48
14. " Fuller cell 50
15. " Cells coupled in series 54
16. " " " Parallel 57
17. Outline of electric bell 61
18. Frame of bell 62
19. E-shaped frame 63
20. Electro-magnet, old form 64
20A. " " modern form 65
21. Magnet frame 66
21A. Winder 72
22. Mode of joining electromagnet wires 73
23. Armature spring 74
24. " " Another form 74
25. Platinum tipped screw 75
26. " " spring 76
27. Binding screws 77
28. Bell or gong 78
29. Pillar and nuts 78
30. Washers 78
31. Trembling bell 81
32. Bell action enclosed in case 88
33. Ordinary trembling bells 90
34. Single stroke bell 91
35. Continuous ring bell 94
36. Release action 95
37. Continuous ringing with relay 96
38. Continuous ringing action with indicator 97
39. Relay and detent lever for indicator 97
40. Callow's attachment 99
40A. Thorpe's arrangement 101
41. Jensen bell, _section_ 102
42. " " _exterior_ 104
43A. Circular bell 106
43B. Mining bell 106
44. Electric trumpet (Binswanger's) 107
45. Various forms of pushes 110
46. Pressel 111
47. Pull 112
48. Bedroom pull 113
49A. " " Another form 114
49B. Floor contact, ball form 114
50. Burglar alarm 115
51. " " Another form 115
52. Floor contact 115
53. Door contact 116
54. Sash contact 117
55. Shop door contact 117
56A. Closed circuit system, _single_ 119
56B. Closed circuit system, _double_ 119
57. Modified gravity, Daniell 120
58. Contact for closed circuit 121
59. Thermometer alarm 122
60. Fire alarm 123
61A. " " Another form 123
61B. " " " " in action 123
62. Binswanger's "watch alarm" contact 125
63. Watchman's electric tell-tale clock 126
64. Lever switch, _two-way_ 128
65. Morse key, _double contact_ 133
66. Relay 134
67. Indicator, drop 137
68. " Semaphore 138
69. " Fall back 139
70. " Pendulum 140
71. " Coupled up 142
72. " Gent's tripolar 143
73. Soldering iron and wires 148
74. Push, interior of 151
75. Bell, battery and push 159
76. " " And earth return 160
77. " and two pushes 161
78. " two pushes and one pull 161
79. Two bells in parallel 162
80. " " Another mode 162
81. " " with two-way switch 163
82. Series coupler 163
83. Bell with local battery and relay 164
84. Continuous ringing bell with wire return 165
85. Bells with Morse keys for signalling 165
86. Bells with double contact pushes for signalling 166
87. Bells with double contact with one battery only 167
88. Two-way signalling with one battery only 168
89. Complete installation of bells, batteries, pushes, etc. 169
90. Mode of getting out plan or design 170
91. Lift fitted with bells 173
92. Magneto bell: generator 174
93. " " Receiver 175
94. " " Combined 176
95. Detector or galvanometer 176
ELECTRIC BELLS.
CHAPTER I.
PRELIMINARY CONSIDERATIONS.
[S] 1. ELECTRICITY.--The primary cause of all the effects which we are
about to consider resides in a force known as _electricity_, from the
Greek name of amber (electron), this being the body in which the
manifestations were first observed. The ancients were acquainted with a
few detached facts, such as the attractive power acquired by amber after
friction; the benumbing shocks given by the torpedo; the aurora
borealis; the lightning flash; and the sparks or streams of light which,
under certain conditions, are seen to issue from the human body. Thales,
a Grecian philosopher, who flourished about 600 years B.C., observed the
former of these facts, but nearly twenty centuries elapsed before it was
suspected that any connection existed between these phenomena.
[S] 2. According to the present state of our knowledge, it would appear
that electricity is a mode of motion in the constituent particles (or
atoms) of bodies very similar to, if not identical with, _heat_ and
_light_. These, like _sound_, are known to be dependent on undulatory
motion; but, whilst _sound_ is elicited by the vibration of a body _as a
whole_, electricity appears to depend, in its manifestations, upon some
motion (whether rotary, oscillatory, or undulatory, it is not known) of
the atoms themselves.
However this be, it is certain that whatever tends to set up molecular
motion, tends also to call forth a display of electricity. Hence we have
several practical means at our disposal for evoking electrical effects.
These may be conveniently divided into three classes, viz.:--1st,
mechanical; 2nd, chemical; 3rd, changes of temperature. Among the
_mechanical_ may be ranged friction, percussion, vibration, trituration,
cleavage, etc. Among the _chemical_ we note the action of acids and
alkalies upon metals. Every chemical action is accompanied by electrical
effects; but not all such actions are convenient sources of electricity.
_Changes of temperature_, whether sudden or gradual, call forth
electricity, but the displays are generally more striking in the former
than in the latter case, owing to the accumulated effect being presented
in a shorter time.
[S] 3. We may now proceed to study a few of these methods of evoking
electricity, so as to familiarise ourselves with the leading properties.
If we rub any resinous substance (such as amber, copal, resin,
sealing-wax, ebonite, etc.) with a piece of warm, dry flannel, we shall
find that it acquires the power of attracting light bodies, such as
small pieces of paper, straw, pith, etc. After remaining in contact with
the rubbed (or electrified) substance for a short time, the paper, etc.,
will fly off as if repelled; and this apparent repulsion will be more
evident and more quickly produced if the experiment be performed over a
metal tray. If a small pith-ball, the size of a pea, be suspended from
the ceiling by a piece of fine cotton, previously damped and then
approached by an ebonite comb which has been briskly rubbed, it will be
vigorously attracted, and never repelled; but if for the cotton there be
substituted a thread or fibre of very fine dry silk, the pith-ball will
be first _attracted_ and then _repelled_. This is owing to the fact that
the damp cotton allows the electricity to escape along it: _id est_,
damp cotton is a CONDUCTOR of electricity, while silk does not permit
its dissipation; or, in other words, silk is a NON-CONDUCTOR. All bodies
with which we are acquainted are found, on trial, to fall under one or
other of the two heads--viz., conductors and non-conductors. Nature
knows no hard lines, so that we find that even the worst conductors will
permit the escape of some electricity, while the very best conductors
oppose a measurable resistance to its passage. Between the limits of
good conductors, on the one hand, and non-conductors (or insulators) on
the other, we have bodies possessing varying degrees of conductivity.
[S] 4. As a knowledge of which bodies are, and which are not, conductors
of electricity is absolutely essential to every one aspiring to apply
electricity to any practical purpose, the following table is subjoined,
giving the names of the commoner bodies, beginning with those which most
readily transmit electricity, or are _good_ conductors, and ending with
those which oppose the highest resistance to its passage, or are
insulators, or non-conductors:--
[S] 5. TABLE OF CONDUCTORS AND INSULATORS.
-----------------+------------------------------+---------------------
Quality. | Name of Substance. | Relative Resistance.
-----------------+------------------------------+---------------------
Good {|Silver, annealed | 1.
Conductors {|Copper, annealed | 1.063
{|Silver, hard drawn | 1.086
{|Copper, hard drawn | 1.086
{|Gold, annealed | 1.369
{|Gold, hard drawn | 1.393
{|Aluminium, annealed | 1.935
{|Zinc, pressed | 3.741
{|Brass (variable) | 5.000
{|Platinum, annealed | 6.022
{|Iron | 6.450
{|Steel, soft | 6.500
{|Gold and silver alloy, 2 to 1 | 7.228
{|Nickel, annealed | 8.285
{|Tin, pressed | 8.784
{|Lead, pressed | 13.050
{|German silver (variable) | 13.920
{|Platinum-silver alloy, 1 to 2 | 16.210
{|Steel, hard | 25.000
{|Antimony, pressed | 23.600
{|Mercury | 62.730
{|Bismuth | 87.230
{|Graphite | 145.000
{|Nitric Acid | 976000.000
| |
Imperfect {|Hydrochloric acid | [1]
Conductors {|Sulphuric acid | 1032020.000
{|Solutions of metallic salts | varies with strength
{|Metallic sulphides | [1]
{|Distilled water | [1] 6754208.000
| |
Inferior {| Metallic salts, solid | [1]
Conductors. {| Linen } |
{| Cotton } and other forms of | [1]
{| Hemp } cellulose |
{| Paper } |
{| Alcohol | [1]
{| Ether | [1]
{| Dry Wood | [1]
{| Dry Ice | [1]
{| Metallic Oxides | [1]
| |
Non-conductors, {| Ice, at 25 c. | [1]
or {| Fats and oils | [1]
Insulators. {| Caoutchouc | 1000000000000.
{| Guttapercha | 1000000000000.
{| Dry air, gases, and vapours | [1]
{| Wool | [1]
{| Ebonite | 1300000000000.
{| Diamond | [1]
{| Silk | [1]
{| Glass | [1]
{| Wax | [1]
{| Sulphur | [1]
{| Resin | [1]
{| Amber | [1]
{| Shellac | [1]
{| Paraffin | 1500000000000.
-----------------+------------------------------+---------------------
[Footnote 1: These have not been accurately measured.]
The figures given as indicating the relative resistance of the above
bodies to the passage of electricity must be taken as approximate only,
since the conductivity of all these bodies varies very largely with
their purity, and with the temperature. Metals become worse conductors
when heated; liquids and non-metals, on the contrary, become better
conductors.
It must be borne in mind that _dry air_ is one of the _best
insulators_, or worst _conductors_, with which we are acquainted; while
damp air, on the contrary, owing to the facility with which it deposits
_water_ on the surface of bodies, is highly conducive to the escape of
electricity.
[S] 6. If the experiment described at [S] 3 be repeated, substituting a
glass rod for the ebonite comb, it will be found that the pith-ball will
be first attracted and then repelled, as in the case with the ebonite;
and if of two similar pith-balls, each suspended by a fibre of silk, one
be treated with the excited ebonite and the other with the glass rod,
until repulsion occurs, and then approached to each other, the two balls
will be found to attract each other. This proves that the electrical
condition of the excited ebonite and of the excited glass must be
different; for had it been the same, the two balls would have repelled
one another. Farther, it will be found that the _rubber_ with which the
ebonite or the glass rod have been excited has also acquired electrical
properties, attracting the pith-ball, previously repelled by the rod.
From this we may gather that when one body acting on another, either
mechanically or chemically, sets up an electrical condition in one of
the two bodies, a similar electrical condition, but in the opposite
sense, is produced in the other: in point of fact, that it is impossible
to excite any one body without exciting a corresponding but opposite
state in the other. (We may take, as a rough mechanical illustration of
this, the effect which is produced on the pile of two pieces of plush or
fur, on being drawn across one another in opposite directions. On
examination we shall find that both the piles have been laid down, the
upper in the one direction, the lower in the other.) For a long time
these two electrical states were held to depend upon two distinct
electricities, which were called respectively _vitreous_ and _resinous_,
to indicate the nature of the bodies from which they were derived. Later
on (when it was found that the theory of a single electricity could be
made to account for all the phenomena, provided it was granted that some
electrified bodies acquired more, while others acquired less than their
natural share of electricity), the two states were known as _positive_
and _negative_; and these names are still retained, although it is
pretty generally conceded that electricity is not an entity in itself,
but simply a mode of motion.
[S] 7. It is usual, in treatises on electricity, to give a long list of
the substances which acquire a positive or a negative condition when
rubbed against one another. Such a table is of very little use, since
the slightest modification in physical condition will influence very
considerably the result. For example: if two similar sheets of glass be
rubbed over one another, no change in electrical condition is produced;
but if one be roughed while the other is left polished, this latter
becomes positively, while the former becomes negatively, electrified.
So, also, if one sheet of glass be warmed, while the other be left cold,
the colder becomes positively, and the latter negatively, excited. As a
general law, _that body, the particles of which are more easily
displaced, becomes negatively electrified_.
[S] 8. As, however, the electricity set up by friction has not hitherto
found any practical application in electric bell-ringing or signalling,
we need not to go more deeply into this portion of the subject, but pass
at once to the electricity elicited by the action of acids, or their
salts, on metals.
Here, as might be expected from the law enunciated above, the metal more
acted on by the acid becomes negatively electrified, while the one less
acted on becomes positive.[2] The following table, copied from Ganot,
gives an idea of the electrical condition which the commoner metals and
graphite assume when two of them are immersed at the same time in dilute
acid:--
{ v Zinc. ^ }
{ v Cadmium. | }
{ | Tin. | }
{ | Lead. | }
{ | Iron. | }
The portion { | Nickel. | } The portion out
immersed in the { | Bismuth. | } of the acid fluid
acid fluid. { | Antimony. | }
{ | Copper. | }
{ | Silver. | }
{ | Gold. | }
{ | Platinum. ^ }
{ v Graphite. ^ }
[Footnote 2: This refers, of course, to those portions of the metals
which are out of the acid. For reasons which will be explained farther
on, the condition of the metals in the acid is just the opposite to
this.]
The meaning of the above table is, that if we test the electrical
condition of any two of its members when immersed in an acid fluid, we
shall find that the ones at the head of the list are _positive_ to those
below them, but negative to those above them, if the test have reference
to the condition of the parts _within_ the fluid. On the contrary, we
shall find that any member of the list will be found to be _negative_ to
any one below it, or _positive_ to any above it, if tested from the
portion NOT immersed in the acid fluid.
[Illustration: Fig. 1.]
[Illustration: Fig. 2.]
[S] 9. A very simple experiment will make this quite clear. Two strips,
one of copper and the other of zinc, 1" wide by 4" long, have a 12"
length of copper wire soldered to one extremity of each. A small flat
piece of cork, about 1" long by 1" square section, is placed between the
two plates, at the end where the wires have been soldered, this portion
being then lashed together by a few turns of waxed string. (The plates
should not touch each other at any point.) If this combination (which
constitutes a very primitive galvanic couple) be immersed in a tumbler
three-parts filled with water, rendered just sour by the addition of a
few drops of sulphuric or hydrochloric acid, we shall get a
manifestation of electrical effects. If a delicately poised magnetic
needle be allowed to take up its natural position of north and south,
and then the wires proceeding from the two metal strips twisted in
contact, so as to be parallel to and over the needle, as shown in Fig.
1, the needle will be impelled out of its normal position, and be
deflected more or less out of the line of the wire. If the needle be
again allowed to come to rest N. and S. (the battery or couple having
been removed), and then the tumbler be held close over the needle, as in
Fig. 2, so that the needle points from the copper to the zinc strip, the
needle will be again impelled or deflected out of its natural position,
but in this case in the opposite direction.
[S] 10. It is a well-known fact that if a wire, or any other conductor,
along which the electric undulation (or, as is usually said, the
electric current) is passing, be brought over and parallel to a
suspended magnetic needle, pointing north and south, the needle is
immediately deflected from this north and south position, and assumes a
new direction, more or less east and west, according to the amplitude of
the current and the nearness of the conductor to the needle. Moreover,
the direction in which the north pole of the needle is impelled is found
to be dependent upon the direction in which the electric waves (or
current) enter the conducting body or wire. The law which regulates the
direction of these deflections, and which is known, from the name of its
originator, as Amp[e']re's law, is briefly as follows:--
[S] 11. "If a current be caused to flow _over_ and parallel to a freely
suspended magnetic needle, previously pointing north and south, the
north pole will be impelled to the LEFT of the _entering_ current. If,
on the contrary, the wire, or conductor, be placed _below_ the needle,
the deflection will, under similar circumstances, be in the opposite
direction, viz.: the north pole will be impelled to the RIGHT of the
_entering_ current." In both these cases the observer is supposed to be
looking along the needle, with its N. seeking pole pointing at him.
[S] 12. From a consideration of the above law, in connection with the
experiments performed at [S] 9, it will be evident that inside the tumbler
the zinc is _positive_ to the copper strip; while, viewed from the
outside conductor, the copper is positive to the zinc strip.[3]
[Footnote 3: From some recent investigations, it would appear that what
we usually term the negative is really the point at which the undulation
takes its rise.]
[S] 13. A property of current electricity, which is the fundamental basis
of electric bell-ringing, is that of conferring upon iron and steel the
power of attracting iron and similar bodies, or, as it is usually said,
of rendering iron magnetic. If a soft iron rod, say about 4" long by
1/2" diameter, be wound evenly from end to end with three or four layers
of cotton-covered copper wire, say No. 20 gauge, and placed in proximity
to a few iron nails, etc., no attractive power will be evinced; but let
the two free ends of the wire be placed in metallic contact with the
wires leading from the simple battery described at [S] 9, and it will be
found that the iron has become powerfully magnetic, capable of
sustaining several ounces weight of iron and steel, so long as the wires
from the battery are in contact with the wire encircling the iron; or,
in other words, "_the soft iron is a magnet, so long as an electric
current flows round it_." If contact between the battery wires and the
coiled wires be broken, the iron loses all magnetic power, and the
nails, etc., drop off immediately. A piece of soft iron thus coiled with
covered or "insulated" wire, no matter what its shape may be, is termed
an "electro-magnet." Their chief peculiarities, as compared with the
ordinary permanent steel magnets or lodestones, are, first, their great
attractive and sustaining power; secondly, the rapidity, nay,
instantaneity, with which they lose all attractive force on the
cessation of the electric flow around them. It is on these two
properties that their usefulness in bell-ringing depends.
[S] 14. If, instead of using a _soft_ iron bar in the above experiment, we
had substituted one of _hard_ iron, or steel, we should have found two
remarkable differences in the results. In the first place, the bar would
have been found to retain its magnetism instead of losing it immediately
on contact with the battery being broken; and, in the second place, the
attractive power elicited would have been much less than in the case of
soft iron. It is therefore of the highest importance, in all cases where
rapid and powerful magnetisation is desired, that the _cores_ of the
electro-magnets should be of the very softest iron. Long annealing and
gradual cooling conduce greatly to the softness of iron.
[Illustration: Fig. 3.
MAGNETS, showing Lines of Force.]
[S] 15. There is yet another source of electricity which must be noticed
here, as it has already found application in some forms of electric
bells and signalling, and which promises to enter into more extended
use. If we sprinkle some iron filings over a bar magnet, or a horse-shoe
magnet, we shall find that the filings arrange themselves in a definite
position along the lines of greatest attractive force; or, as scientists
usually say, the iron filings arrange themselves in the direction of the
lines of force. The entire space acted on by the magnet is usually known
as its "field." Fig. 3 gives an idea of the distribution of the iron
filings, and also of the general direction of the lines of force. It is
found that if a body be moved before the poles of a magnet in such a
direction as to cut the lines of force, electricity is excited in that
body, and also around the magnet. The ordinary magneto-electric machines
of the shops are illustrations of the application of this property of
magnets. They consist essentially in a horse-shoe magnet, in front of
which is caused to rotate, by means of appropriate gearing, or wheel and
band, an iron bobbin, or pair of bobbins, coiled with wire. The ends of
the wire on the bobbins are brought out and fastened to insulated
portions of the spindle, and revolve with it. Two springs press against
the spindle, and pick up the current generated by the motion of the iron
bobbins before the poles of the magnet. It is quite indifferent whether
we use permanent steel magnets or electro-magnets to produce this
effect. If we use the latter, and more especially if we cause a portion
of the current set up to circulate round the electro-magnet to maintain
its power, we designate the apparatus by the name of DYNAMO.
[Illustration: Fig. 4.
TYPICAL DYNAMO, showing essential portions.]
[S] 16. Our space will not permit of a very extended description of the
dynamo, but the following brief outline of its constructive details will
be found useful to the student. A mass of soft iron (shape immaterial)
is wound with many turns of insulated copper wire, in such a manner
that, were an electrical current sent along the wire, the mass of iron
would become strongly north at one extremity, and south at the other. As
prolongations of the electro-magnet thus produced are affixed two masses
of iron facing one another, and so fashioned or bored out as to allow a
ring, or cylinder of soft iron, to rotate between them. This cylinder,
or ring of iron, is also wound with insulated wire, two or more ends of
which are brought out in a line with the spindle on which it rotates,
and fastened down to as many insulated sections of brass cylinder placed
around the circumference of the spindle. Two metallic springs,
connected to binding screws which form the "terminals" of the machine,
serve to collect the electrical wave set up by the rotation of the
coiled cylinder (or "armature") before the poles of the electro-magnet.
The annexed cut (Fig. 4) will assist the student in getting a clear idea
of the essential portions in a dynamo:--E is the mass of wrought iron
wound with insulated wire, and known as the _field-magnet_. N and S are
cast-iron prolongations of the same, and are usually bolted to the
field-magnet. When current is passing these become powerfully magnetic.
A is the rotating iron ring, or cylinder, known as the _armature_, which
is also wound with insulated wire, B, the ends of which are brought out
and connected to the insulated brass segments known as the
_commutator_, C. Upon this commutator press the two springs D and D',
known as the _brushes_, which serve to collect the electricity set up by
the rotation of the armature. These _brushes_ are in electrical
connection with the two terminals of the machine F F', whence the
electric current is transmitted where required; the latter being also
connected with the wire encircling the field-magnet, E.
When the iron mass stands in the direction of the earth's magnetic
meridian, even if it have not previously acquired a little magnetism
from the hammering, etc., to which it was subjected during fitting, it
becomes weakly magnetic. On causing the armature to rotate by connecting
up the pulley at the back of the shaft (not shown in cut) with any
source of power, a very small current is set up in the wires of the
armature, due to the weak magnetism of the iron mass of the
field-magnet. As this current (or a portion of it) is caused to
circulate around this iron mass, through the coils of wire surrounding
the field-magnet, this latter becomes more powerfully magnetic ([S] 13),
and, being more magnetically active, sets up a more powerful electrical
disturbance in the armature.
This increased electrical activity in the armature increases the
magnetism of this field-magnet as before, and this again reacts on the
armature; and these cumulative effects rapidly increase, until a limit
is reached, dependent partly on the speed of rotation, partly on the
magnetic saturation of the iron of which the dynamo is built up, and
partly on the amount of resistance in the circuit.