Year: 1887

page_text: Date of Application, 2nd Sept., 1887
Complete Specification Left, 2nd July, 1888
Complete Specification Accepted, 3rd Aug., 1888
I JOSEPH WILSON SWAN of Laureston Bromley in the County of Kent Gentleman
do hereby declare the nature of this Invention to be as follows :-
My Invention has for its object to diminish the danger of explosions of fire damp
in Coal mines or other places.
It consists of an improved apparatus capable of indicating continuously and auto-
matically the proportion of fire damp (marsh Gas) in admixture with atmospheric air.
According to my Invention I employ a differential air thermometer formed of an
upright tube of glass with mercury or other liquid in the bend and with each limb
of the U terminating in a bulb. Passing into or through each of the bulbs, and
sealed into them there is a tube containing a thin platinum wire. The tube in one of
the bulbs is closed so that the atmospheric air which it contains and which surrounds
the platinum wire is never changed. The other tube in the other bulb is open and
therefore the air within it which surrounds the other platinum wire, varies in
composition with the varying condition of the air of the mine in which the apparatus
is placed.
The platinum wire in the closed tube and the platinum wire in the open tube are
connected together in series and joined in the circuit of a Voltaic battery or other
generator of Electricity of sufficient power to maintain them at a red heat.
The apertures of the open tube, containing the red hot wire, are covered with wire
gauze, and I may further guard against the passage of fire to the outer air by placing
the apparatus or a portion of it within a box or casing formed partly or entirely of
wire gauze.
When the apparatus is surrounded with air free from fire-damp, the wires within
the thermometer bulbs are equally hot, and the air-pressure is equal upon the surface
of the mercury or other liquid in each limb of the U tube and the two columns of
mercury or other liquid are therefore equal in height.

page_text: When fire-damp is present in the air, the platinum wire in the open tube becomes
hotter than that in the closed tube and the air pressure is greater on' the hotter side,
consequently the mercury or other liquid is depressed on that side and correspondingly
raised on the other side. A greater or less difference of height of the liquid in the
two limbs of the U tube therefore indicates (within limits) a greater or less proportion
of fire-damp in the air.
If in any case it is required that an audible signal shall be given on the accumu-
lation to a certain amount of fire damp in the air, I make the following addition to
the apparatus as described.
On that side of the U tube which has the platinum wire completely closed within
the bulb I seal a short piece of platinum-wire through the wall of the U tube, with
one end projecting thereinto slightly above the zero point of the liquid (which in this
case is mercury) and with the other end projecting on the outside of the tube and
1 seal another similar piece of platinum wire through the tube lower down so that its
inner end is always immersed in the mercury and its outer end projects from the
outside of the tube. Conducting wires are continued from these two platinum wires
to the terminals of a generation of electricity which may be the battery employed to
make the platinum wires in its path the magnet coil of an ordinary electro-magnetic
bell or signalling device. The upper wire of the two thus sealed through the U tube
and connected to the bell circuit will when the air is pure be out of contact with the
mercury in the U tube and consequently the bell circuit will be incomplete but when
fire damp is present in sufficient proportion to cause the column of mercury to rise
and touch the upper wire the bell circuit will be completed and the bell will ring.
With the view of simplifying the apparatus and avoiding the use of the electric
current for heating the wires I sometimes modify the arrangement described by
employing instead of a differential thermometer a differential balance that is to say
instead of employing heat as the motive power of the apparatus I in that case employ
gravity. In this modification of the inductor the difference in the specific gravity of
pure atmospheric air and of air mixed with fire damp is the cause of the indication.
The apparatus depending on this principle may take the form of a pair of light glass
bulbs of equal size fixed on the top of the stems of a pair of Hydrometers of sufficient
floating power to keep the bulbs erect and above the liquid in which the hydrometers
float. The bulbs are placed side by side in a small tank containing a suitable liquid
such as Glycerine and Water and one of the bulbs is covered by a receiver or vessel
containing pure air while the other is exposed to the air of the mine. If the stems
float at an equal height in pure air they will float at different heights if the air of the
mine or portion of which is displaced by one of the bulbs is mixed with fire-damp in
consequence of the less specific gravity of such mixture and the difference of floatation
will show the extent of the contamination. Instead of supporting the air displacement
bulbs by means of Hydrometers as described I may employ a pair of scale beams or a
pair of spiral springs for that purpose.
DL: 11
1
1004
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C.,
Agents.

page_text: I JOSEPH WILSON SWAN of Lauriston Bromley in the County of Kent 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:-
My Invention has for its object to diminish the danger of explosions of fire damp
in coal mines or other places. It consists of an improved apparatus capable of
indicating continuously and automatically the presence of fire-damp (Marsh gas) in
admixture with atmospheric air, the said apparatus having for its essential feature the
combination of two wires or resistances of equal gauge in contact respectively with
atmospheric air and with the atmosphere of the mine or place, the atmosphere of
which is to be tested and a differential thermometer, by which the difference between
the temperatures of the two wires or resistances is caused to give an indication of the
presence of explosive gas or to signal when such gas is present to any pre-determined
extent. I will describe, with reference to the accompanying drawings, the best ways
with which I am acquainted of carrying my invention into effect. Referring first to
Figure 1, employ a differential air thermometer formed of an upright U tube A
preferably of glass with mercury or other liquid in the bend and with each limb of
the U tube terminating in a bulb or chamber (B and C).
Passing into or through each of the bulbs or chambers and sealed into them there
is a tube containing a thin platinum wire. The tube D in the bulb or chamber C is
closed, so that the atmospheric air which it contains and which surrounds the platinum
wire d within it, is never changed. The other tube E, in the bulb or chamber B is
open at both ends, and therefore, the air which it contains and which surrounds the
other platinum wire e, varies in composition with the varying condition of the air ot
the mine or place in which the apparatus is used. The platinum wire d, in the
closed tube D, and the platinum wire e, in the open tube E, are connected together
in series and joined in the circuit of a voltaic battery or other generator of electricity
of sufficient power to maintain them at a dull red heat. The electric current may
be derived from the battery of an electric safety lamp in conjunction with which the
apparatus may be used. The apertures of the open tube E are covered with wire
gauze with a view to prevent the flame which may be caused by contact of the hot
wire e, with an explosive atmosphere, from being conveyed to a similarly explosive

page_text: atmosphere outside the tube. The wire gauze e may be protected by perforated
metal caps, as at e. I may further guard against the passage of fire to the outer air
and protect the apparatus against injury by placing it, or a portion of it, within a
metallic box or casing F, having perforated sides at f, covered internally with wire
gauze ƒ³.
The exterior of the case F may be provided with an adjustable perforated cover F
capable of being moved so that the perforations in it coincide with those in the
casing For so that they do not so coincide and thus the external atmosphere may be
admitted to the apparatus or not as desired.
The wires d, e, may of course enter the tubes at any convenient place and the
details of construction may, it will be evident, be greatly varied, without departing
from the nature of my invention. e and dare glass beads to keep the wires rigid
and in position and are straps or rings to hold the tubes or chambers D and E in
position.
The action of the apparatus is follows
:-
When the apparatus is surrounded with air, free from fire damp, the wires de
within the bulbs or chambers DE are by the passage of an electric current made
equally hot, and consequently the air pressure is equal upon the surface of the mercury
or other liquid in each limb of the U tube A, and the two columns of mercury or other
liquid are therefore equal in height.
When fire-damp is present in the air, the platinum wire e in the open tube E
becomes hotter than does the platinum wire d in the closed tube D and the air
pressure consequently becomes greater on the hotter side, and the mercury or other
liquid is depressed in the leg of the Ụ tube on the hotter side, and is correspondingly
raised in the leg of the U tube on the other side. A greater or lesser difference of
height of the liquid in the two limbs of the U tube therefore indicates a greater or
lesser proportion of fire-lamp in the air up to the limit at which the gas and
atmospheric air form the most explosive or combustible mixture. The U tube may
be marked or furnished with a scale for readily ascertaining the amount of gas
present.
If in any case it be required that an audible or visible signal shall be given on the
accumulation to a certain extent of fire damp in the air, I make one or other of the
following additions to the apparatus hereinbefore described. To make the apparatus,
so as to give audible signals. On that side of the U tube A which has the platinum
wire d, completely enclosed within the bulb D 1 scal a piece of platinum wire g,
through one leg of the U tube at any suitable part thereof and with one end
projecting thereinto, so as to be situated above the zero level of the liquid (which in
this case is mercury) and with the other end projecting on the outside of the tube and
I seal another piece of platinum wire h through the other leg of the U tube at any
suitable part thereof and so that its inner end is always immersed in the mercury,
and its outer end projects from the outside of the tube. Conducting wires ii are
continued from these two platinum wires to the circuit of a generator of electricity
(which may be the battery employed to light a lamp and to heat the platinum wires
of the indicator) and which also includes the magnet coil of an electro magnetic bell
or signalling device J, which may be of any ordinary or suitable kind as I do not
restrict myself to the particular arrangement of such bell illustrated in the drawings.
The wire g will, when the air of the mine or other place is pure or practically so, be
out of contact with the mercury in the U tube and consequently the bell circuit will
be incomplete, but when fire damp is present in sufficient proportion to cause, as
aforesaid, the column of mercury to rise so that it touches the wire g the electric
circuit which includes the bell will be completed and the bell will ring.
e
Or in place of the sounding of an audible signal I may, when an electric lamp is
used with my apparatus, cause the lamp to be extinguished when there is a dangerous
amount of gas present. To effect this I include the wires g and h in the lamp circuit
but I make both the wires g and h normally in contact with the mercury so that when
the mercury is depressed in the leg of the U tube on the side at which the open

page_text: tube E is situated the circuit to the lamp is broken and the light will consequently be
extinguished.
I may provide a bridging as at x so that the lamp can be relighted by turning the
switch y whilst the wires d and e are cut out of the circuit.
I do not limit myself to the use of air thermometers as illustrated in Figure 1 as
it will be evident that other kinds of thermometers can be used to cause the making
or breaking of the electric circuit and the consequent action of the signal.
Figures 2 and 3 of the accompanying drawings shew in front elevation and
horizontal section respectively an arrangement of two thermometers A A' each
consisting of a helical tube of oval or double convex section and containing liquid
and acting on the principle of what is known as Immisch's thermometer. The two
thermometers A A' are fixed in a perforated box F lined with wire gauzef and
enclosed in an outer casing F² also perforated with holes corresponding to the holes
in box F. The outer casing F2 is capable of being turned on the inner casing F
(or vice versa) so as to close the perforations to prevent the entrance of air to the
interior of the box or open then to admit the air as required. The thermometer
coils A A² are arranged side by side and in the interior of the coils are the tubes D
and E containing the wires ed. The ends a a² respectively of the two coils A A² are
attached to the interior of the box F but electrically insulated from it and also to the
respective poles of the battery which are also electrically insulated whilst their
opposite ends are free but are in contact with each other so as to complete an
electric circuit through the coils. The ends 62 should be shaped so that, when the
coils expand and contract owing to the ordinary varying temperature of the atmosphere,
they will remain in contact to maintain the electric circuit. For this purpose the
end of the coil A' may be curved as shewn at c to engage a stirrup or projection c
on the end b of the coil A so that they will remain in contact so long as the two coils
expand and contract equally. When however by reason of the presence of explosive
gas the wire in the tube E becomes more highly heated than the wire in the tube D
the coil A will expand to a greater extent than the coil A2 and cause the ends b
to separate and thereby interrupt the electric circuit and extinguish the light of the
electric lamp in the same circuit. If desired instead of the ends bb separating when
the coil E expands the said ends may normally be out of contact and be made to
come into contact when the expansion of the coil takes place and thereby establish an
electrical circuit to give an indication or signal by means of a bell or other device
included in the circuit which they then complete.
Figures 4 and 5 represent in vertical section and horizontal section respectively
another modification in which the two helical tubular thermometers are arranged one
above the other instead of side by side as in the arrangement last described. The
perforated box or case F containing the coils A A² is preferably cylindrical and is
surrounded by an outer perforated cylinder F2 screwed into a socket F attached to
the miners electric lamp or to other suitable support. The box or casing F is arranged
to turn in the outer casing F* for the purpose of opening and closing the perforations
when required; the distance to which it is permitted to turn for this purpose being
governed by a screw f1 passing through a slot in the outer casing and screwed into
the inner casing. In the bottom of the tube F2 is a block or disc G of steatite or
other suitable insulating material and to the upper surface of this block are screwed
two plates g, g², the one g being provided with a socket g³ forming a foot step, bearing
for the rotating box or cylinder F. To this plate g is connected one pole of the
battery whilst the other conductor after passing through the lamp is connected to the
plate In the lower end of the inner box or casing F is secured (by screws h or
otherwise) a block or disc H of steatite or other suitable material to which the lower
end a of the coil A2 is connected by a bolt and nut a¹ or otherwise. In the upper end
of the box or cylinder F is fitted another block or disc I of steatite or other suitable
material to which the upper coil A' is connected by the bolt and nut b¹ or otherwise.
The free ends bb' of the coils A and A' carry each a projecting piece c c which in
their normal position are in contact with each other. The tubes D and E are arranged

page_text: within the coils A and A2 and are supported in sockets i¹¹ the sockets ¹ ♬ in
which the tube E is fitted being perforated as shewn at for the purpose of admitting
the external gases as hereinbefore described, the perforations being covered on the
inside of the sockets with wire gauze e². The sockets and are respectively
secured by nuts and to the blocks or discs I and H whilst the sockets and k¹
are connected together by a screw formed on the one and screwing into the other, a
disc of mica or other suitable material being interposed as shewn at 12. The wires d and e
in the tubes D and E are attached to stems m which enter holes in the sockets i¹² k¹ k³
and are secured therein by screws as shewn. The stem on the lower socket k³ by
which it is secured to the disc H passes through the said disc and forms a pivot o
upon which turns the foot step bearing 9. To the underside of the disc H is secured
a bow spring or contact piece which, when the inner case F is turned so as to open the
apertures therein, is brought into contact at one of its ends with the pole plate g so as
to complete the circuit through the indicator the lamp and the battery and which when
the case is turned so as to close the said apertures bridges the plates g² and g and cuts
the indicator out of the battery and lamp circuit.
P
When the circuit is completed so as to include the indicator the current from the
battery is through the foot step bearing g pivot o socket wire d sockets k¹ and
wire e socket and by the plate and screw to the coil A thence by the contact
pieces to the coil A2 and by the screw a spring contact p and plate g² to the
battery.
The wires and e will under ordinary conditions of the atmosphere then become
equally hot but if fire damp be present the wire e in the open tube E will become
hotter than will the wire d in the closed tube D and the coil A will in consequence of
the increased heat expand to a greater extent than will the coil A³ and cause the
contact pieces cc to separate and thereby break the electric circuit in which the lamp is
included. When the apparatus is not required for use or when by the action of fire
damp the light has been extinguished the cylinder F is turned in the outer case or
cylinder F so as to cover the perforations in the cylinders F and F and this action
brings the one end of the bow contact spring p into contact with the plate g the other
end remaining in contact with the plate and thus short circuits the plates g g³
thereby closing the circuit which includes the lamp and battery and cutting out the
indicator.
Instead of arranging the contact pieces pg and g³ so that on turning the tube F
to close the apertures the indicator wire will be cut out of the lamp circuit as described,
I may arrange them in such a manner that in remaking the broken circuit by turning
the tube as before said the indicator wires shall still be included in the circuit the
thermometric portion only being cut out. Figures 6 and 7 shew in vertical section
and plan respectively an arrangement by which this may be effected-An additional
metallic plate is attached to the lower disc H and insulated from the spring contact p.
This plate carries a spring contact piece p2 and is connected by a wire p³ with the
upper central plate 3 to which the upper coil A is connected. The springs p and p
are arranged so that on turning the tube F to close the apertures therein the spring
contact p will be moved out of contact with the plate g² and thereby break the circuit
through the coils A, A2 and at the same time the spring contact piece p* will make
contact with the said plate g², the current being then from the battery through the
plate g and footstep bearing g³ pivot o socket k² wire d socket k¹ and wire e socket i¹
plate side wire p³ spring contact p³ and plate g³ to the battery.
Having now particularly described and ascertained the nature of my said Inven-
tion and in what manner the same is to be performed I declare that what I
claim is,
1. In apparatus for indicating the presence of fire damp in coal mines or other
places the combination with wires or resistances respectively protected from and
exposed to the atmosphere of the mine or other place of a differential thermometer
and means for giving an indication or signal of the presence of fire-damp substantially

page_text: as hereinbefore described whether there be or be not used in combination therewith a
bell or audible signal which is given or sounded or a lamp which is extinguished when
a dangerous amount of gas is present.
2. The combination of a differential thermometer with electrically heated exposed
and non-exposed wires and an electric lamp in such a manner substantially as herein-
before described as to cause extinction of the light in the presence of fire-damp.
3. The several arrangements of apparatus for the purpose herein before stated and
substantially as herein before described and illustrated in Figure 1 in Figures 2 and 3
in Figures 4 and 5 and in Figures 6 and 7 of the accompanying drawings.