Improvements in Apparatus for Detecting and Estimating the Proportion of Fire-damp or other Inflammable Gases in the Atmosphere of Mines and other Spaces.
Year: 1893

page_text: Date of Application, 22nd June, 1893
Complete Specification Left, 22nd Mar., 1894-Accepted, 21st Apr., 1854
PROVISIONAL SPECIFICATION.
Improvements in Apparatus for Detecting and Estimating the
Proportion of Fire-damp or other Inflammable Gases in the
Atmosphere of Mines and other Spaces.
GEORGE FLETCHER 59, Wilson Street Derby Teacher of Science do hereby
declare the nature of this invention to be as follows:-
This invention relates to apparatus for detecting and estimating the proportion
of fire-damp or other inflammable gases in the air of mines and other spaces.
The action of the instrument which constitutes my invention depends upon the
well-known fact that a luminous spiral of wire glows more brightly when the
surrounding air contains a small proportion of some inflammable gas such as
hydrogen or methane. The instrument consists of two spirals of fine platinum
wire. one of which is contained in an air-tight tube containing air, and having
the upper end closed by glass. The other spiral is contained within a tube of
wire gauze having the upper end also closed by glass. These tubes are placed
within a box or case (hereinafter called the outer case) and a suitable current of
electricity allowed to pass through both spirals. If the spirals are similar as
regards material and dimensions the spirals will glow with equal brightness and
may be observed through a screen of ground glass or other suitable substance.
The outer case is divided into two compartments by an opaque screen, each
compartment containing one of the tubes hereinbefore described.
apparatus be placed in an atmosphere containing an inflammable gas such as
fire-damp the spiral placed within the wire-gauze tube will glow more brightly,
and the luminosity of the spiral will increase with the proportion of the inflammable
gas present. These changes may be observed by reference to the ground glass
screen.
If now the
In order to estimate the percentage of gas present the relative distance between
the tubes and ground glass screen is varied. This is accomplished by means of a
rack and pinion. The pinion is fixed between the tubes containing the spirals,
each one being provided with a rack. The pinion is turned by means of a milled
screw placed outside the outer case and the wire gauze tube moves away from the
screen while the other approaches it. The pinion is turned until the illuminated
portions of the screen are equally bright. The distance through which the pinion
is turned is indicated by a pointer fixed to the spindle and moving over a graduated
circle marked on the outside of the outer case. This circle is in the first place
graduated by experiment with measured percentages of gas and so when used
indicates directly the percentage of gas present.
As a source of electricity I employ any convenient form of primary or secondary
battery of suitable electromotive force and which may be employed to light an
incandescence lamp when a test is not being made. Inside the outer case is a
resistance switch by means of which the circuit can be opened or closed and a
suitable resistance inserted in order to raise the spirals to any desired state of
incandescence. This switch consists of a circular disc of any suitable insulating
material with a wire of some high-resistance metal such as German-silver fixed
round its periphery. This ring of wire is not quite complete and one end of it is
connected to the axis of the disc. A small spring presses against the periphery
and the circuit to the spirals is completed through this spring, the resistance wire
and axle. In a certain position of the disc the spring presses against its insulating
material and the circuit is broken. On turning the disc the spring presses against
the wire, completing the circuit, and the resistance may be reduced until a suitable

page_text: state of incandenscence in the spirals is obtained by turning the disc through a
smaller or larger angle. The conducting wire leading from the spirals are flexible.
The outer case is provided with suitable terminals or connecting pieces which
allow it to be conveniently fixed to the source of electricity.
The outer case is provided with tubes by means of which gas may be introduced
from any desired space by aspiration or otherwise.
Dated this 21st day of June 1893.
GEORGE FLETCHER.
COMPLETE SPECIFICATION.
Improvements in Apparatus for Detecting and Estimating the
Proportion of Fire-damp or other Inflammable Gases in the
Atmosphere of Mines and other Spaces.
I GEORGE FLETCHER of 59, Wilson Street, Derby, Teacher of Science 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 :-
.
This invention relates to apparatus for detecting and estimating the proportion
of fire-damp or other inflammable gases in the air of mines and other spaces. The
action of the instrument which constitutes my invention depends upon the observed
fact that a luminous spiral of wire glows more brightly when the surrounding air
contains a small percentage of some inflammable gas or vapour such as hydrogen
or methane.
The instrument consists of two spirals of fine platinum wire, one of which is
contained in an air-tight tube T containing pure atmospheric air and having the
upper end closed by a disc of glass a or other suitable transparent substance. The
other spiral is contained within a tube of wire gauze T having the upper end
also closed by glass or other suitable substance. These tubes are placed within a
box or case which is provided with tubes t and t¹ for the free admission of the
surrounding air. This case is partially or completely divided into two compartments
by the partition p. The tubes T and T¹ slide inside two other tubes B and B'.
To each of the inner tubes is fixed a rack r and which engage with the pinion P
which is turned by a milled screw N placed on the outside of the case. The outer
tubes B and B are slotted to permit the racks to work up and down. The platinum
spirals S and S are connected to stout upright wires which pass through air-tight
plugs of ebonite fitted in the lower ends of the tubes T and T¹. They are
connected in series with each other by a flexible wire w and, by means of flexible
wires to the connecting pins p³ and p after passing through the resistance switch
shewn in Figure 3. The construction of this switch is as follows: D is an ebonite
disc turning about the axle A. It is fitted within the case and can be rotated
about its axle by means of a milled screw S which is placed outside the case.
Round the periphery of this disc is a wire of German-silver or other substance of
high electrical resistance. One end of this wire is connected to the axle against
which presses a spring a. Another spring a¹ presses against the periphery of the
wheel. In the position shewn in Fig. 3 it rests against the ebonite the circuit
being broken. On rotating the disc in the direction shown by the arrow the
spring a¹ presses against the resistance wire and by turning it through a greater
angle the resistance in circuit can be diminished.
As a source of electricity I employ a miner's electric lamp or any other suitable
primary or secondary battery, provided with suitable contact pieces. The course
of the current is from pl through the spiral s¹ the connecting wire w the spiral s
the spring a' of the resistance switch the German-silver wire, spring a to p³. The
resistance switch is, for the sake of clearness omitted from Fig. 1. I will now
describe how the instrument may be employed for measuring the proportion of

page_text: inflammable gas in the atmosphere surrounding the instrument. When it is desired
to make the test the resistance switch is turned round until the current passing
raises the spirals to a suitable degree of luminosity. As they are of equal
dimensions they glow with equal brightness if the surrounding air be free of
inflammable gas. The light emitted by each may be compared by looking down
upon the screen W which is made of glass or other suitable translucent substance.
If, however, there should be a small percentage of inflammable gas present in the
Burrounding air it is found that the spiral enclosed in the wire gauze tube glows
more brightly. The relative distance of the spirals from the screen W is now
varied by rotating the milled screw N in such a direction that the tube T moves
towards while T¹ moves away from W and until the two halves of the screen are
equally illuminated. The angle through which the pinion has been turned is read
by reference to a dial on the outside of the case, a needle u being attached to the
pivot as shown in Fig. 2. The percentage of inflammable gas present may also
be observed from the dial which is in the first place graduated by experiment with
measured percentages of inflammable gas in air. The source of electricity may
be employed to light a small incandescence lamp when a test is not being made.
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. The arrangement and combination, in apparatus for detecting and estimating
inflammable gas, of tubes rackwork screen and dial substantially in the manner
described.
2. The application of a screen of translucent material for photometric purposes
to an electrical instrument for measuring the percentage of inflammable gas in air.
3. The application of an indicating dial in an instrument for measuring the
proportion of inflammable gas in air.
4. The form and arrangement of resistance switch for the purpose of regulating
an electric current substantially as described.
5. The combination of a resistance switch with an instrument for measuring the
proportion of inflammable gas in air.
6. The combination of a miner's electric lamp with an instrument for measuring
the proportion of inflammable gas in air.
Dated this 20th day of March 1894.
GEO FLETCHER
GEO FLETCHER