Method of and Apparatus for Detecting and Indicating the Presence of Fire-damp or other Noxious Gas or Gases in the Atmosphere of Mines and other Places.
Year: 1895

page_text: Date of Application, 28th Sept., 1895
Complete Specification Left, 29th June, 1896-Accepted, 28th Dec., 1896
Method of and Apparatus for Detecting and Indicating the Presence
of Fire-damp or other Noxious Gas or Gases in the Atmosphere
of Mines and other Places.
We, ERHARD LUDWIG MAYER, of 11 Billiter Square, in the City of London,
Engineer, and GEORGE BUSH, of 3 Gracechurch Street, in the City of
London, Gentleman do hereby declare the nature of this invention to be as
follows:-
According to this invention the presence of fire-damp or other noxious gas or
gases in the atmosphere of mines and other places is detected and indicated by
causing such gas or gases to generate by means of a gas battery, charges of static
electricity that are caused to operate or control means or apparatus whereby a
visual or audible signal, or both, are brought into operation to give an indication
of a change in the constitution of the atmosphere in which the battery is
placed.
The statical charges of electricity produced by the gas battery alone, or in
conjunction with another suitable source of electricity, may act by attraction,
or repulsion, or both, to effect or control either directly or indirectly move-
iment of the means employed for producing a visual signal or an audible signal,
or both.
Apparatus to operate on the principle of my invention can be constructed in
various forms. In one arrangement the terminals of the gas battery are connected
to two metallic sheets or plates which are insulated from each other and one of
which is arranged to be oscillated, reciprocated or otherwise moved by clockwork
or other suitable mechanism. The other sheet or plate is arranged to be stationary,
except when both of the said metallic sheets or plates become oppositely charged
with static electricity, whereupon it is held by attraction to the first by which it is
moved and caused to produce a signal, as for instance by bringing an electric
bell into circuit, by shunting sufficient current from an electric lamp to visibly affect
the illuminating power thereof, or by operating a shutter.so as to cut off more or
less of the light of a lamp.
In another arrangement, one terminal of the gas battery is connected to a pair
of movable conductors suspended in proximity to two pairs of fixed conductors
connected to the opposite poles of another source of electricity, preferably of high
potential; or the fixed conductors may be connected to the gas battery and the
movable ones to one pole of the other source of electricity. The fixed conductors
may be of sheet metal or foil carried by a circular support of opaque insulating
material in which is a hole through which the light of a lamp, for example a miner's
lamp, can pass under ordinary conditions of the atmosphere.
The movable conductors, which may also be of sheet metal or foil and be bent
and arranged so as to be concentric with the fixed ones, carry a shutter adapted to
control the aforesaid hole, the arrangement being such that upon both of the
sets of conductors being charged with static electricity, the movable conductors
will be caused to partly rotate and come opposite to the aforesaid hole,
thereby shutting off more or less or otherwise modifying the supply of light
aud so indicating the presence of fire-damp or other noxious gas in the atmosphere.

page_text: It will be seen that I employ in this arrangement a device similar to the quadrant
electrometer.
In another arrangement, use is made of a device similar to the Bohnenberger
electroscope or its modifications.. In this case one terminal of the gas-battery is
connected to earth and the other to a leaf or thin flexible sheet of aluminium,
gold, or other suitable material, supported by one edge between a pair of conductors
that are connected to the opposite poles of another source of electricity, preferably
of high potential; or the fixed conductors may be connected to the gas-battery and
the flexible sheet to the other source of electricity. The fixed conductors and the
flexible sheet may be contained in a dry atmosphere in a hermetically sealed case,
which is partly or wholly made of glass or other suitable transparent material.
In suitable positions relative to the flexible sheet, there is provided a lamp and a
selenium cell, the arrangement being such that the flexible sheet normally prevents
rays from the lamp from reaching the selenium cell but allows them to do so when
the flexible sheet is deflected towards one of the fixed conductors by the action of
the gas-battery. A slight current normally passes through the selenium cell; but
when the cell is acted upon in this way by the rays from the lamp, its resistance is
reduced to such an extent as to allow an amount of current to pass through it
sufficient, if necessary with the aid of a relay, to ring a bell or to put a danger screen
before the lamp, or both. The lamp employed may be an electric one, in which
case the arrangement may be such that when the selenium cell is acted upon in this
way the additional current that passes through it may be taken from the lamp, so
as to reduce the light given out thereby. If the lamp be one by which a miner
works, the reduction may be such as to compel the miner to cease work although
not so much as to prevent him from seeing his way in the mine.
The same results may also be brought about without the aid of a second-source
of electricity by an arrangement resembling the ordinary gold-leaf electroscope,
its two leaves being connected to the same pole of the gas battery and the other
pole of this battery being connected to earth. This same arrangement may also
be used in connection with the condenser arrangement hereinbefore described, and
in conjunction with a selenium cell. The sheets or plates or condensers may be
supplied with a mirror to reflect the light upon the cell or otherwise.
The selenium cell is also applicable to the arrangement in which a device
resembling the ordinary quadrant electro-meter is used; in this case the light may
be reflected by a mirror fixed axially to the movable conductor or conducting plate
or plates so as to be thrown, when a certain angle of deflection has been reached,
upon the selenium cell.
A suitable selenium cell for use as described, comprises two metallic gratings
connected together by selenium and so arranged that a considerable surface of
selenium can be exposed to the rays of light. Such a cell may be formed of two
metallic frames one of which surrounds the other and on each of which are
arranged and secured by solder or other suitable means, so as to be in electrical
connection therewith, a number of parallel wires. Between the smaller of these
frames and its wires there are fixed pieces of mica or other suitable non-conducting
material, on which rest the wires of the other frame, the arrangement being such
that the wires of the two frames alternate and that there is no electrical connection
between the two frames or their respective wires. The two frames are or may be
held between two plates of glass or other suitable material and the interstices
between the frames and their wires, completely filled with selenium, the finished
cell being subsequently annealed in such a manner as to make the selenium
sensitive to light.
A gas-battery suitable for any of the arrangements hereinbefore described
comprises a normally closed box provided with means for enabling it to be filled
with ordinary atmospheric air and also with a device-for example, a flexible
diaphragm or ball-for ensuring that the pressure within the box shall be equal to
that outside it. In one or more of the walls of this box there are inserted, in
suitable non-conducting material and so as to be in contact both with the air inside

page_text: and with the air and gas outside the box, pieces of porous non-conducting
material-for example, fire-clay, papier mâché, or plaster of Paris-which are
arranged at suitable distances apart and are impregnated with an acid-for
example, suitably diluted sulphuric acid-which acts as the electrode of the
battery, the porous pieces being connected in series by their external and internal
ends by means of some suitable conducting material. The porous pieces may
project inwardly and outwardly as regards the box and their projecting ends may
be provided with suitable metallic caps, the external cap of each piece being
connected by a wire with the internal cap of a consecutive piece, and so on; or
connecting wires may be simply coiled round the projecting ends of consecutive
pieces, so as to form good contact therewith. Or the porous pieces may not
project from the wall or walls of the box, in which case consecutive pieces may be
connected together by strips of sheet platinum or other suitable material, which,
when of platinum, are preferably made with their surfaces of spongy platinum
and each of which has one of its ends inserted in one of the porous pieces and has
its other end connected by a wire, that passes in an air-tight manner through the
non-conducting material of the wall of the box, to another similar strip of
platinum inserted; at the other side of the box envelope, in a consecutive porous
piece.
To set the battery, the box is charged with air of ordinary purity, by drawing
air from the external atmosphere through it and then closing it. Both ends of all
the porous pieces being then in a like medium, there is equilibrium of action and no
generation of electricity takes place, but upon the composition of the air external
to the box being sufficiently changed, as for example as is likely to take place in
coal mines by mixture with the air of marsh gas, i.e. fire damp, a charge of static
electricity will be set up in the conductors connected therewith.
Dated this 28th day of Sentember 1895.
Method of and Apparatus for Detecting and Indicating the Presence
of Fire-damp or other Noxious Gas or Gases in the Atmosphere
of Mines and other Places.
We, ERHARD LUDWIG MAYER, of 11 Billiter Square, in the City of London,
Engineer, and GEORGE BUSH, of 3 Gracechurch Street, in the City of London,
Gentleman do hereby declare the nature of this invention and in what manner
the same is to be performed to be particularly described and ascertained in and
by the following statement:-
According to this invention the presence of fire-damp or other noxious gas or
gases in the atmosphere of mines and other places is detected and indicated by
causing such gas or gases (hereinafter referred to as fire-damp) to generate by
means of a gas battery, charges of static electricity that are caused to operate or
control means or apparatus whereby a visual or audible signal, or both, are brought
into operation to give an indication of a change in the constitution of the atmosphere
in which the battery is placed.
The statical charges of electricity produced by the gas battery- alone, or in
conjunction with another suitable source of electricity, may act by attraction, or
repulsion, or both, to effect or control either directly or indirectly movement of
the means employed for producing a visual signal or an audible signal, or both..

page_text: .
Apparatus to operate on the principle of this invention can be constructed in
various forms.
Figs. 1 and
of the accompanying drawings are elevations at right angles to
each other showing, diagrammatically, one arrangement in which the terminals of a
gas battery 1 (a construction of which is hereinafter described) are connected by
insulated conductors 2 and 3 to two metallic sheets or plates 2 and 3 respectively,
which are insulated from each other and one of which (2) is arranged to be moved
to and from the other (3) which is arranged to be stationary except when both of
the said metallic sheets or plates (hereinafter called plates) become oppositely
charged with static electricity, whereupon it will be held, by attraction to the first
plate 2 by which it will be moved and caused to produce a signal. The plate 2 is
carried by an insulating strip 2b pivoted at its upper forked end 2° upon supports 4
80 that it can be oscillated from time to time by clockwork 5 through an insulated
link 5. The plate 3, which is carried by an insulating strip 3b pivoted between a
pair of screws 4, is provided with an insulated contact 6, which by sufficient
movement of the plate 3, is brought against a spring contact 6ª so as to complete
the circuit of a battery 7 through an electric bell 8 which will then give an audible
signal. Or the bringing of the contacts 6, 6* against each other may be arranged
to shunt sufficient current from an incandescent electric lamp 8" (Fig. 1) to
visibly affect the illuminating power thereof and so give a visual signal. Or the
movement of the plate 3 may be caused to operate, as by an electro-magnet 8b, the
circuit of which is closed by the contacts 6, 6, an annunciator shutter 8° so as to
cut off more or less of the light of a lamp that normally passes through an
opening 8 in a suitable screen. The bell, lamp and shutter may be used
simultaneously, as in the example shown in Fig. 1, or one or the other may be used
alone.
The plate 2 is preferably made thick enough to permit of the surface thereof
facing plate 3 being made as nearly a true plane as possible. The plate 3 should be
made as light as possible, and be very delicately pivoted so that a comparatively
low E.M.F. will be sufficient to hold it (by attraction) against the plate 2 until the
angle through which the latter plate is moved by clockwork or otherwise is large
enough to suit the practical requirements of the arrangement. One way of
attaining this end is to stretch a light and flexible sheet, for example india rubber,
over a light aluminium frame 3° (Figs. 3 and 4) and provide it on the side facing
plate 2, with a conductive surface, for example of aluminium leaf, corresponding in
size with plate 2 and in connection with conductor 3 by which means the flexible
sheet will be held, by the force of attraction, to the plain surface of plate 2 when a
sufficient difference of electrical potential is set up between the two plates. The
movement imparted to the plates by clockwork or otherwise is preferably of such
a nature that the two plates will remain in undisturbed contact for, say 5 or 10
minutes, and that the pull afterwards exerted upon plate 2 shall be slow and
gradual, so that, in case the two plates are held together simply by air pressure, air
shall have time to interpose itself between them and so bring about their separation
before the plate 3 shall have been moved sufficiently to close the circuit of the
battery 7 and cause a signal. The layer 2d of insulation that separates the two
plates 2 and 3, may advantageously consist of a film of hard varnish applied to
plate 2, as this will enable the layer of insulation to be easily made of even thickness
and with a plain surface. The thickness of this insulation is, of course, kept as
small as practicable..
Fige. 5 and 6 show respectively in side elevation and plan, another arrangement
in which one terminal of the gas battery 1 is connected to a pair of movable
conductors 9 that are suspended by a wire 9* and cross bar 9b so as to be in
proximity to two pairs of fixed conductors 10 that are connected to the opposite
poles of a second source of electricity, for example a battery 11, preferably of
high potential say about 50 to 100 volts, the second pole of the gas battery
being placed to earth E. The fixed conductors 10 may be of sheet metal or
foil carried by a circular support 12. of opaque insulating material in which is

page_text: a hole or holes 13 through which the light of a lamp 14, for example an oil
lamp or an incandescent electric lamp, can pass under ordinary conditions of the
atmosphere.
The movable conductors 9 which may also be of sheet metal or foil and are bent
and arranged so as to be concentric with the fixed ones 10, carry a shutter 9° or
may be themselves made to serve as shutters, adapted to control the passage of
light through the holes 13. The arrangement is such that upon both sets of
conductors 9 and 10 being charged with static electricity, the movable conductors 9
will be caused to partly rotate and thereby shut off more or less or otherwise
modify the passage of light through the holes 13 and so indicate the
presence of fire-damp in the atmosphere in which the gas battery 1 is placed. It
will be seen that in this arrangement a device similar to a quadrant electrometer
is employed.
Fig. 7 is a perspective view showing another arrangement in which an ordinary
simple form of Lord Kelvin's quadrant electrometer is used for closing an electric
circuit and sounding an audible signal. The electrometer consists of a metal box
cut into four quadrants, each well insulated from the other, one pair of opposite
quadrants 10 being connected to one pole of a battery 11 of suitably high potential
say 50 to 100 volts, and the other pair 10° to the other pole of this battery.
Between the upper and lower surfaces of the quadrants is suspended a needle 9" of
the shape usual in these instruments, this needle being suspended by a very fine
metallic (platinum) wire 9 so that it can swing freely. The needle is charged with
static electricity through the wire 9" when the gas battery 1 is excited. Below the
quadrants, the wire 9* carries a piece of insulating material 14 with platinum wire 15
and a light metallic arm 15º, the wire and arm being in electrical connection with
each other. The wire 15 dips into a liquid, for example sulphuric acid, contained
in a receptacle 17 and connected by a conductor 18 to one pole of a battery 19 the
other pole of which is connected through a relay R with an adjustable contact 6*
against which a contact 6 on the arm 15ª will be brought, so as to complete a signal
controlling circuit when the needle 9* receives a sufficient charge of static electricity
from the gas battery 1 and is consequently deflected by the charged quadrants 10, 10ª.
In this way the movement of the needle can be caused to produce an audible signal;
or it may be a visual signal; or both audible and visual signals if desired, either
directly or, as in the arrangement shown, by a relay brought into action by the
bringing together of the contacts 6, 6*.
With a quadrant electrometer arrangement, such as shown in Fig. 7, it is
preferred to use a switch adapted to serve three different purposes viz. (a) after
contact between 6 and 6* has taken place, to short circuit the gas battery Ì so that
the latter can return to the inactive state provided that the fire-damp mixed with
the air to be tested, has been removed therefrom by means of effective ventilation ;
(b) to interrupt the primary relay circuit, and (c) to cut out both the relay and an
electro magnet belonging to the switch, at the same time leaving the signalling
device in action until the switch has been re-set for a new indication. This switch
has the further advantage that it is incapable of being re-set whereby the signalling
device, for example a bell, would become inactive, before the fire-damp has been
removed by ventilation from the place in which the air is being tested, so that the
bell will be kept ringing until this has been done. The switch comprises a disc 16
of insulating material loaded at one side and carrying two pairs of contacts
viz. 16* 16 and 16° 16°, each pair being connected by a strip of metal. Around
the disc are six spring contacts 16, 16', 16, 16¹, 16¹, and 16*. The spring contact 16°
is connected to one terminal of the battery 19, the spring contact 16 to one terminal
of the primary or actuating circuit of the relay R the other terminal of which is
connected to the contact 6; the spring contacts 168 and 16h are connected to the
two terminals of the gas battery 1 the contact 16 being also connected to the
needle 9 and the contact 168 being also connected to earth; the contact 16' is
connected to one terminal of the electric bell 8 the other terminal of which is
connected to one pole.of.the.battery 19ª and the remaining contact 16* is connected

page_text: to the other pole of the battery 19*. This pole is also connected to one viz. 16' of
the two terminals of the auxiliary relay circuit, the other terminal 16" of which is
connected to the contact 16' through an electromagnet 16" having a spring arma-
ture 16º that normally engages with a projection 16º on the disc 16 and holds the
same in the position shown. With the parts in the positions shown, the instrument
is in condition for detecting the presence of fire-damp. On the gas battery becoming
excited by presence of fire-damp, the contacts 6, 6 will be brought together by the
deflection of the needle 9* and the primary relay circuit closed. The auxiliary
relay circuit will be consequently completed, whereby the bell 8 will be set in action
and the armature 16° will attract the electro-magnet 16" and release the disc 16
which will then turn automatically until arrested by a stop 16%. The spring
contact 16 and 16 will then bear upon the disc contact 16° 16° and so short
circuits the relay R and electro-magnet 16" leaving the bell in action. The spring
contacts 16 and 16" will at the same time bear upon the disc contacts 16° and 164
and short circuits the gas battery. 16" is a handle for resetting the switch. The
fixed conductors 10 (Figs. 5 and 6) or 10 10 (Fig. 7) may be connected to the two
poles of the gas battery 1, and the movable conductors 9 (Figs. 5 and 6) or
conductor 9 (Fig. 7) to one pole of the second source of electricity 11, the other
pole of which is then placed to earth.
The signalling arrangement with primary and auxiliary relay circuits and
switch shown in Fig. 7 may be combined with the arrangement shown in Figs. 5
and 6.
Fig. 8 is a side elevation and Fig. 9 a plan showing, diagrammatically, another
arrangement in which use is made of a device similar to the Bohnenberger electro-
scope. One terminal of the gas battery 1 is connected to earth E as before, and
the other to a leaf or thin flexible sheet 21 of aluminium, gold, or other suitable
material, supported by one edge and placed perfectly symmetrically between a
pair of conductors 22, 22, which are connected to the opposite poles of another
Bource of electricity, for example a battery 23 of high potential, say about
five hundred volts or still better, much higher, the charge on the plate 21 being
also one produced by many hundreds of gas cells. Or the fixed conductors 22, 22"
may be connected to the poles of the gas-battery and the flexible sheet to one pole
of the battery 23 the other pole of which is then connected to earth. The fixed
conductors 22, 22 and the flexible sheet 21 are contained in a dry atmosphere in
a case 22 which may be hermetically sealed and be partly or wholly made of glass
or other suitable transparent material. In suitable positions relative to the flexible
sheet 21, there is provided a lamp 14 and a selenium cell 24, the arrangement
being such that the flexible sheet 21 normally prevents rays 14* from the lamp
reaching the selenium cell (Figs. 8 and 9) but allows them to do so when the
flexible sheet 21 receives a static charge from the gas battery and is consequently
deflected towards the fixed conductors 22, as indicated in dotted lines in Fig. 8.
A slight current normally passes through the selenium cell 24 from a battery 25,
but when the cell is acted upon by the rays from the lamp 14, its resistance is
reduced to such an extent as to allow an amount of current to pass through it
sufficient, (if necessary with the aid of a relay) to ring a bell 8, or to put a danger
screen before the lamp, (but so as not to affect the light falling on the selenium
cell) or both. If the lamp be one by which a miner works, the reduction of light
caused by the movement of the screen, may be such as to compel the miner to
cease work although not such as to prevent him from seeing his way in the mine.
Fig. 10 is a side elevation showing diagrammatically another arrangement
embodying the principle of Bohnenberger's electroscope. 22 and 22ª are two
metallic plates of suitable thickness, having their adjacent surfaces made as true
planes as possible, and arranged parallel with one another, at a short distance
apart. Plate 22 remains stationary; plate 22" can be oscillated, for example in
the manner and by the means hereinbefore described with reference to Figs. 1
and 2. These plates, which are insulated from each other as for example by
coating them with hard varnish, form the terminals of a battery 23 of high

page_text: potential, for example a battery consisting of a number of small cells of the
Leclanche or other suitable type, giving say 50 to 100 volts. 21 is a third plate
delicately suspended between the other two and connected to one pole of the gas
battery 1 the other pole of which is connected to earth. The plate 21 carries an
insulated contact 6 adapted to close the circuit of a battery 7 through a signalling
device 8 when it abuts against the spring contact 6ª. With this arrangement
plate 21 will, under normal conditions, be attracted in an equal degree by both
plates 22, 22ª assuming that the position of plate 21 is accurately symmetrical to
these plates. Upon plate 22" being moved to the left, plate 21, will, if it be
uncharged by the gas battery, simply obey the influence of gravity and remain at
rest, and as 22 recedes, will be firmly held to the plate 22 by attraction due to
induction. If, however, plate 21 receives from the gas battery 1 a slight charge,
say a few volts, of electricity of the same sign as that of plate 22, and therefore,
opposite to that of plate 22, it will be repelled by plate 22 and attracted by
plate 22 and will therefore follow the movement of the latter and cause a signal
to be produced in the manner hereinbefore described with reference to Figs. 1
and 2. In practice, it will be found convenient to have the thin and light sheet
composing plate 21, metallically coated on each of its two sides, and to place the
two sides in electrical connection with one another so that when the plate is lightly
pressed by the plain surface of plate 22 against the plain surface of plate 22, the
seat of the induced static charges of opposite signs, on either side of the sheet, will
be equi-distant from the insulated surfaces of the two plates 22 and 22ª. It is
preferred to so construct the apparatus that when all the plates are practically
perpendicular, plate 21 has a slight tendency to follow the movements of plate 22.
By then slightly tilting the whole system to the right (Fig. 10) a position can be
found when plate 21 owing to gravity, will just remain in contact with plate 22,
instead of following the plate 22 when the latter is withdrawn to the left, provided
that no extra charge has been imparted to it, but if an excess of potential opposite
in sign to that of plate 22 and, therefore, of the same sign to that of plate 22, is
given to plate 21 by means of the gas battery 1, the plate 21 will be repelled by
plate 22, and follow the movement of plate 22. Before plate 22 is pulled out of
its parallelism with plate 22, it is advisable that the electrical connection between
it and the battery 23 should be interrupted, and maintained so as long as its
movement lasts, in order that its potential may not fall on account of the increase
of distance from plate 22, which it is about to undergo. For this purpose, on the
rod 5 connected to the clockwork 5 for oscillating the plate 22, is a block 25 of
insulating material provided with extensions 25, 25, one of which, viz. 25ª, is
adapted, when the rod 5* moves to the left, to pull a contact 26, connected with
one pole of the battery 23, away from the plate 22ª, the extension 25° afterwards
engaging an insulated projection 27 on the plate 22" and moving the same
outward.
The plate 3 or 21 in the condenser arrangements (Figs. 1 and 2 and Fig. 10)
may be fitted with a mirror adapted to reflect a beam of light falling thereon upon
a selenium cell as soon as the desired degree of angular movement of the plate has
been reached, instead of directly actuating an audible signal by a contact arrange-
ment as shown.
Similar results to those herein before described may also be brought about
without the aid of a second source of electricity by an arrangement such as that
shown in Figs. 11 and 12 which resembles the ordinary gold-leaf electroscope, its
two leaves 21, 21" being connected to the same pole of the gas battery 1 the other
pole of which is connected to earth. 22° 22° are two plates in inductive relation to
the leaves 21, 21* respectively and connected with earth. In this case however it
would be necessary to use a gas battery having a very high E.M.F. say 500 volts
so that it is better to use in conjunction with this arrangement two condenser
plates 22, 22" that are well insulated from one another and one of which viz. 22" is
capable of being moved close up to the other, and then separated. These two
plates are connected with the two poles of the gas battery 1 and one of them.

page_text: viz. 22, with the two gold leaves 21, 21%. When the plates 22, 22" are very close
together, they will be charged from the gas-battery with electricity of opposite
sign and of much higher potential than the gas battery otherwise can supply. Oa
then disconnecting the condenser plate 22" from the gas battery, and thereafter
removing it, (still well insulated) to a distance from the plate 22 the high potential
on plate 22 will spread equally over it and the connected gold-leaves, and cause
the latter to diverge from one another in the usual manner, so that the beam of
light, in the path of which they had been interposed, can then fall upon the
selenium cell 24.
A selenium cell is also applicable to the arrangements shown in Figs. 5, 6 and 7.
In this case the light may be reflected by a mirror fixed axially to the wire 9* that
suspends the needle 9* (or conductors 9), so as to be thrown, when a certain angle
of deflection has been reached, upon the selenium cell. With an arrangement like
that shown in Figs. 5 and 6, the selenium cell may be placed inside the case and
just behind the hole 13 therein which is so arranged as to be normally covered by
a shutter 9° of non-conducting material carried by the adjacent conductor 9 and
which uncovers the hole and allows the light of the lamp to fall on the cell and
produce a signal when the conductors 9 are deflected by receiving a charge from
the gas battery.
As the force exerted by the displacement of the needle 9" in the quadrant
electrometer arrangement (Fig. 7) is exceedingly small, it sometimes happens that
the electric current does not pass between the two platinum wire contacts 6, 6* for
completing the circuit controlling the signalling device, although they are actually
bearing against one another. This difficulty can be overcome by coating the
adjacent surfaces of the platinum wires with a thick layer of spongy platinum, or
still better, by providing the ends of the two wires as shown, with two small plates
of platinum each of about half to one square inch in area and coated with spongy
platinum, which may conveniently be done electrolytically. By this means when-
ever the plates come into close and parallel proximity to one another, the attractive
forte set up between them, aided by the well known action of points, invariably
causes an effective contact between them and the passage of an electric current
to take place. The use of spongy platinum also prevents the usual sticking
together of the two uncoated platinum wires, due to some welding action of the
electric current at the point where it has been passing from one wire to the other.
In order to still further increase the attraction between the two plates a
battery 19 (Fig. 7) having a comparatively high E.M.F. say, 10 to 20 volts, may
be employed, care being taken that the resistance in circuit is high enough to
prevent a larger current flowing than is necessary for the work it is to perform.
This construction of contact is not herein claimed as forming part of the present
invention, but I contemplate including it in a separate application for Letters
Patent.
A suitable selenium cell for use as described, comprises two metallic gratings
connected together by seleuium and so arranged that a considerable surface of
selenium can be exposed to rays of light.
.
Fig. 13 is a plan and Figs. 14 and 15 vertical sections on the lines a x and y y
respectively of Fig. 14, showing one arrangement of such a selenium cell. "It
comprises two metallic frames 28 and 29, one of which (29) surrounds the
other (28), and on each of which are arranged and secured, so as to be in
electrical connection therewith, a number of parallel wires 30 and 31 respectively.
For this purpose, the frames may be notched at the edges and the wires passed
in a zig-zag. direction around the resulting projections so that the parallel
portions of wire are all on the same side of the frames and parallel with each
other as shown. Between the smaller of these frames 28 and its wires 30 there
are fixed pieces of mica or. other suitable non-conducting material on which rest
the wires of the other frame, the arrangement being such that the wires of the
two frames alternate and that there is no direct electrical connection between
the two frames or their respective wires. The two frames are, or may be, held

page_text: between two plates of glass 32, 32 or other suitable transparent material, one
of which, 32, rests directly upon the platinum wires, and the interstices between
the frames and their wires is completely filled with selenium. The finished cell is
subsequently annealed in such a manner as to make the selenium sensitive to light.
This may be effected by allowing the cell to remain for about half an hour at a
temperature just below the melting point of the selenium. Terminal wires are
connected to the plates 28 and 29.
my inven-
Fig. 16 is a front elevation and Fig. 17 a horizontal section on the line of
Fig. 16, showing a construction of gas battery suitable for carrying out
tion. It comprises a normally hermetically closed box provided with an inlet 34
and outlet 35 for enabling it to be filled with ordinary atmospheric air, and also
with a device-for example, a very flexible diaphragm or ball 36, for ensuring that
the pressure within the box shall be equal to that outside it. In one, or it may be
more, of the walls of this box there are inserted, in suitable non-conducting material
and so as to be in contact both with the air inside and with the air and gas outside
the box, pieces of porous non-conducting material 37-for example, fire-clay,
papier-mache, plaster of Paris, or compressed glass wool,-which are arranged at
suitable distances apart and are impregnated with a suitable electrolyte, for
example, diluted sulphuric acid-consisting of say one part by weight of acid to
four or six parts by weight of water according as the atmosphere to be tested is
moist or dry. The porous pieces are connected in series by connecting their
external and internal ends by means of some suitable conducting material such as
platinum. The porous pieces may project inwardly and outwardly as regards the
box, and their projecting ends may be connected by wires or strips 38 simply
coiled round the projecting ends of consecutive pieces so as to form good contact
therewith. Or the ends of the pieces 37 may be provided with tightly fitting
metallic caps or rings 39 (Fig. 18), the external cap or ring of each piece being
connected by a wire 38 with the internal cap or ring of a consecutive piece and so
Or the ends of the porous pieces may not be flush with the surface of the
wall of the box, as shown in Fig. 19, and the consecutive pieces may be connected
together by strips 38, (Fig. 19) or by wires, of platinum or other suitable
conductive material, which, when of platinum, are preferably made with their
exposed surfaces of spongy platinum and each of which has one of its ends inserted
in one of the porous pieces 37, and its other end, after passing in an air-tight
manner through the wall of the box, in a consecutive porous piece at the other
side of the wall of the box.
on.
If the battery is to be set up in the place where noxious gas, such as fire-damp,
accumulates, the box is charged with air of ordinary purity, by drawing air from
the external atmosphere through it and theu closing it. Both ends of all the
porous pieces being then in a like medium, there is equilibrium of action and
no generation of electricity takes place, but upon the composition of the air
external to the box being sufficiently changed, as for example as is likely
to take place in coal mines by admixture with the air of marsh gas, i.e., fire-
damp, a charge of static electricity will be set up in the conductors connected
therewith.
A battery of the kind described having say five dozen cells or elements
properly connected will, if the atmosphere in which the battery is placed contains
say 4% to 5% of marsh gas, have an electro-motive force of about 3 volts which
is sufficient for the arrangements shown in Figs. 5, 6, 7 and 10. For the other
arrangements a higher voltage is necessary as hereinbefore mentioned which can
be obtained by increasing the number of porous pieces or elements.
The whole of the parts constituting each of the arrangements hereinbefore
described may be placed in the mine or other place the atmosphere in which is to
be tested; or the gas battery only may be located in such place and the difference of
potential set up thereby conducted to the place where the rest of the apparatus is
set up, and the signals thereby produced transmitted to wherever it may be useful
that they should become known. The difference of potential of the gas battery.is
B

page_text: best transmitted to the indicating apparatus by means of two highly insulated
wires arranged in close proximity to one another so as not to be injuriously affected
by the inductive effect of other sources of electricity. It is also advisable to
connect the middle of the gas battery 1, or of the battery 11 (Figs. 5, 6 and 7)
or 23 (Figs. 8, 9 and 10) supplying the high potential, to earth, in cases where one
pole of such battery is not connected to earth, so as to ensure that the pro-
portionality between the potential differences of the two batteries shall remain
unaffected by earth currents. For this purpose the earth connection of the two
batteries may be made in close proximity to one another, or by means of one and
the same earth plate.
The gas battery instead of being put in the mine or other place the air in which
is to be tested, may obviously be placed in any other convenient place, as for
example at the surface of the mine, and the air to be tested be conveyed to it by
means of a pipe through which it is caused to flow in contact with the inner ends
of the elements 37, the outer ends of which are then exposed to the ordinary outer
atmosphere. The air to be tested may be drawn along the pipe and through the
gas battery by suction produced by a chimney or other suitable means.
Apparatus such as shown in Figs. 1, 2, 10, 11 and 12 may be used on board ship
for testing the atmosphere of coal bunkers or the like. In this case the condenser
or electrometer arrangements that serve to detect the presence of static charges of
electricity produced by the gas battery, should be mounted on gimbals so as not to
be affected by the motion of the ship.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. Detecting and indicating the presence of fire damp in the atmosphere of
mines and other places by causing such fire damp to produce electricity by the aid
of a gas battery and utilizing such electricity to operate or control means or
apparatus whereby a signal will be produced.
2. The herein described method of detecting and indicating the presence of fire-
damp or other noxious gas or gases in the atmosphere of mines and other places
by causing such gas or gases to generate by means of a gas battery static
electricity and utilizing said static electricity to operate or control means or
apparatus whereby a visual or audible signal, or both an audible and visual signal
is or are produced to give an indication of a change in the constitution of the
atmosphere in which the gas battery is placed as set forth.
3. For carrying out the method referred to in the preceding claim, apparatus
comprising a gas battery, two movable conducting plates connected to the terminals
of the said battery, arranged parallel and close together but insulated from each
other, means for directly moving one of said plates, and a signalling device the
action of which is controlled by the other of said plates, the arrangement being
such that the second plate will remain practically stationary until both plates are
oppositely charged with static electricity by the gas battery and are held together
by attraction whereupon it will be moved by the first plate and produce a signal
substantially as described.
4. For carrying out the method referred to in Claim 1, apparatus comprising
fixed and movable conductors arranged in proximity to each other, a gas battery
connected with one of the conductors or sets of conductors and a second electric
generator connected to the other remaining conductor or conductors so as to
constantly charge the same with static electricity when the apparatus is in use, and
a signalling device under the control of the movable conductor or conductors, the
arrangement being such that when the gas battery is excited and charges the
conductor or conductors connected therewith with static electricity, the movable
conductor or conductors will be set in motion and cause a signal to be produced
substantially as described.
14
5. The modified arrangement of apparatus wherein the movable conducting

page_text: plate for controlling the signalling device is placed between two other insulated
conducting plates that are arranged parallel and near together and one of which is
connected with a device by which it can be intermittently moved towards and from
the other which is stationary, and the gas battery is connected to the one plate or
to the two plates and the second electric generator to the two last mentioned plates
or to the first plate, as the case may be so as to constantly charge the same with
static electricity the arrangement being such that the first mentioned plate will
remain at rest until the gas battery comes into action when it will be held by
attraction to and moved by the intermittently operated plate, substantially as
described.
6. Apparatus of the kind referred to in Claims 3 and 4 in which the signalling
device is controlled by an electric circuit having a selenium cell therein, and a lamp
or burner the light from which is caused to fall on the selenium cell and produce a
signal when the movable conductor (or conductors) in the one case, or the movable
third plate into the other, is moved by reason of the gas battery coming into action
substantially as described.
7. In apparatus of the kind herein referred to, a gas battery comprising a
normally closed box carrying in one or more of its walls a number of pieces of
porous non-conducting material that are insulated from each other, are impregnated
with a suitable electrolyte and are connected in series by suitable conducting
material that joins the inner end of the several pieces with the outer ends of the
next adjacent pieces substantially as hereinbefore described with reference to the
several examples shown in Figs. 16 to 19, inclusive of the drawings annexed.
8. For detecting and indicating the presence of fire-damp or other noxious gas
or gases in the atmosphere of mines and other places, apparatus constructed
arranged and operating substantially as herein before described with reference
respectively to and shown in Figs. 1 to 4 inclusive; in Figs. 5 and 6; in Fig. 7;
in Figs. 8 and 9; in Fig. 10; in Figs. 11 and 12 of the drawings annexed, or
modified as set forth.