IMPROVEMENTS IN APPARATUS FOR INDICATING AND " MEASURING FIRE-DAMP IN MINES
Year: 1879

page_text: LETTERS PATENT to George Forbes, of Glasgow, in the County of Lanark,
North Britain, M.A., Professor of Natural Philosophy in Anderson's College,
for the Invention of IMPROVEMENTS IN APPARATUS FOR INDICATING AND
"
MEASURING FIRE-DAMP IN MINES."
Sealed the 6th February 1880, and dated the 13th August 1879.
Sealed the 6th February 1880, and dated the 13th August 1879.
PROVISIONAL SPECIFICATION left by the said George Forbes at the Office
of the Commissioners of Patents on the 13th August 1879.
GEORGE FORBES, of Glasgow, in the County of Lanark, North Britain, M.A.,
Professor of Natural Philosophy in Anderson's College. "IMPROVEMENTS IN
APPARATUS FOR INDICATING AND MEASURING FIRE-DAMP IN MINES."
This Invention has for its object the combining of parts to form a simple,
portable, convenient, and reliable instrument for indicating and measuring fire-
damp in mines, such instrument acting on the principle of ascertaining the density
of the air by means of a musical note, and thence inferring the proportion of fire-
damp present from its effect in modifying the density of the air with which it is
mixed.
For producing the musical note the instrument is provided with a tuning fork of
definite pitch, and this tuning fork is held by a bracket by preference of brass or
other metal, which can be clamped or otherwise fixed to a variable resonator, so
that the points of the tuning fork are in front of the mouth of the resonator. The
resonator is by preference a metal tube fitted with a piston or plunger by the
adjustment of which the length of the interior of the tube, that is, the resonant
cavity can be varied. The piston or plunger is conveniently made of a tube of a
size to slide within the resonator tube, and its outer end is fitted with a handle
which is by preference made of ebonite or other material which does not easily
conduct heat, whilst a similar handle, but of a tubular form, is fixed on the resonator
tube near its outer end. The resonator tube is held by one hand, whilst the sliding
or piston tube is held and adjusted by the other hand, and when using the instru-
ment, the tuning fork having been sounded the piston tube is adjusted in the position
which is found to yield the maximum sound of the musical note. A point or
projection fixed on the sliding or piston tube acts on a small rack fitted to slide in
11

page_text: a guide on the resonator tube, and this rack gears with a pinion on the arbor of a
pointer fitted to move over a suitably graduated dial attached to the resonator
tube. A spring is provided to return the pointer and rack to their normal
positions. By this means the indications obtained by adjusting the piston tube so
that the maximum sound is yielded are shown on a sufficiently enlarged scale. It
is desirable to correct the indications thus obtained for variations of temperature,
and for this purpose a thermometer is conveniently fitted upon the bracket which
holds the tuning fork. A special scale is marked beside the thermometer with
suitably calculated numbers, which are to be subtracted from the indications on
the dial attached to the resonator tube in order to obtain corrected readings.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said George Forbes in the Great Seal Patent Office on the 11th February
1880.
GEORGE FORBES, of Glasgow, in the County of Lanark, North Britain, M.A.,
Professor of Natural Philosophy in Anderson's College. "IMPROVEMENTS IN
APPARATUS FOR INDICATING AND MEASURING FIRE-DAMP IN MINES."
: My said Invention has for its object the combining of parts to form a simple,
portable, convenient, and reliable instrument for indicating and measuring fire-damp
in mines, such instrument acting on the principle of ascertaining the density of the
air by means of a musical note, and thence inferring the proportion of fire-damp
present from its effect in modifying the density of the air with which it is mixed.
For producing the musical note my instrument is provided with a tuning fork of
definite pitch, and this tuning fork is held by a bracket fixed to a variable resonator
so that the points of the tuning fork are in front of the mouth of the resonator.
The resonator is by preference a metal tube fitted with a piston or plunger by the
adjustment of which the length of the interior of the tube, that is, the resonant
cavity can be varied. The resonator tube is held by one hand whilst the piston or
plunger is adjusted by the other hand, and when using the instrument, the tuning
fork having been sounded the piston or plunger is adjusted in the position which is
found to yield the maximum sound of the musical note. The instrument is fitted
with a graduated dial on which the indications are shown on an enlarged scale, and
which may be either stationary with a pointer moving over it, or movable under
a stationary pointer, the moving part in either case having attached to it a pinion
which gears with a rack moving with the piston or plunger. It is desirable to
correct the indications obtained in the manner hereinbefore described for variations
of temperature, and for this purpose a thermometer is conveniently fitted upon the
bracket which holds the tuning fork. A special scale is marked beside the ther-
mometer with suitably calculated numbers, which are to be subtracted from the
indications shown on the dial attached to the resonator tube in order to obtain
corrected readings.

page_text: And in order that my said Invention and the manner of performing the same may
be properly understood I hereunto append a Sheet of explanatory Drawings, to be
hereinafter referred to, and representing two modifications of the "Damposcope," as
I designate my improved instrument for indicating and measuring fire-damp in
mines. In these Drawings the same reference numerals are used to mark the same
or like parts wherever they are repeated.
Figures 1 and 2 on the accompanying Sheet of Drawings are an end view and
a side elevation of one modification of the Damposcope; and Figure 3 is an enlarged
section of part of the instrument as turned over relatively to Figure 2. In this
modification the tuning fork 8 is fixed by means of a pinching screw 9, in a socket
at the end of a bracket 10, which when the instrument is used is clamped by means
of a pinching screw 11 on the end of a tube 12; this tube 12, the interior of
which constitutes the resonant cavity, has fixed on it a tubular handle piece 13,
which is by preference of ebonite or other suitable material not readily conducting
heat, the tube itself being of brass or other suitable material. Inside of the resonator
tube 12 there is a piston or plunger 14, which is conveniently made of a metal tube
with its inner end closed, and which has at its outer end a handle 15 of ebonite or
other suitable material. The piston or plunger 14 is entered into the resonator tube
12 from the end opposite to that at which the tuning fork 8 is held, and when
pushed in as far as it will go it leaves a length of resonant cavity at least as small
as any that will be required. The resonant cavity is lengthened by drawing out
the piston or plunger 14, which may be completely withdrawn for the purpose of
charging the resonant tube with the air or mixture of gases which it is wished to
test. A point or projection 16 fixed in the side of the piston or plunger 14 projects
through a slot in the side of the resonator tube 12, and bears against one end of
a toothed rack 17 fitted to slide in guides on the outside of the resonator tube. The
rack 17 gears with a pinion 18, on the arbor of which there is fixed a pointer 19
arranged to move over a suitably graduated dial 20 attached to the resonator tube.
The face of the dial 20 is by preference coated with a phosphorescent substance so
as to show the indications in the dark. A volute spring indicated by dotted lines
at 21, in Figure 3, and contained in a small box at the back of the dial 20 is
connected to the arbor of the pointer 19 and pinion 18 so as to return these and the
rack 17 to their normal positions, an arrangement which allows of the piston or
plunger 14 being completely withdrawn without deranging the connection with the
pointer 19. A thermometer 22 is attached to the bracket 10, and a scale beside it
is marked with the numbers, which, as herein before explained, require to be sub-
tracted from the indications on the dial 20 to give readings corrected for differences
of temperature.
Figure 4 represents a convenient instrument for sounding the tuning fork by the
end 23, being slightly larger than the space between the ends of the prongs, and
the instrument being used by drawing the end 23 between the prongs.
Figures 5, 6, and 7 represent a second modification of the Damposcope having
some parts a little more advantageously and conveniently arranged than in that
shown in Figures 1, 2, and 3. In this second modification the inner tube 14 has
the rack 17 fixed to it, and the pinion 18 is fixed to the dial 20 which is mounted
so that it can be turned by hand, whilst a stationary pointer 24 is fixed so as to
project over the front of the dial and indicate the extent to which the dial is turned
and thereby show the movement of the tube 14 and the length of the resonant
cavity. The tube 14 has passing through it a rod 25 having a piston 26 at its
inner end and a handle 27 at its outer end, and the rod 25 is long enough to allow
of the piston 26 being moved quite to that end of the resonator tube 12, at which
the tuning fork 8 is held. When the piston 26 is thus moved it drives the air or
gas completely out of the resonant cavity, and when the piston is afterwards drawn
in, the instrument being then held in the atmosphere or mixture of gases to be
tested, it draws a portion of such atmosphere or gaseous mixture into the resonant
cavity. In this way it is easy to make certain that the gaseous mixture in the
resonant cavity is that which it is wished to test. When the piston 26 has been

page_text: drawn in close to the inner end of the tube 14 it is locked to that tube by turning
the rod 25 so as to move a projection 28 thereon under the end of the tube, as in a
bayonet joint, and then the tube 14 and piston 26 can be moved as one piece by
turning the dial 20, which acts by means of the pinion 18 and rack 17.
Amongst other modifications of which the details of the instrument are suscep-
tible is the making of the inner tube 14 adjustable by screwing it into or out of the
resonator tube, and fixing the dial or indicating scale in a flat or cylindrical form on
either of the tubes, the pointer being on the other tube. The thermometer may also
be arranged to act automatically, thus in the case of a mercurial thermometer it
may be placed on.or beside the dial so that the variable end of the'mercury consti-
tutes the point at which the dial indication is to be read; or the pointer may be
held by a composite metallic arm on which heat acts differentially.
Having thus particularly described my said Invention, and the manner of
performing the same, I have to state that I do not restrict myself to the precise
details herein described or delineated, but that what I believe to be novel and
original, and claim as the Invention secured to me by and in terms of the herein-
before in part recited Letters Patent, is,-
The arranging or combining together of the parts of apparatus for indicating and
measuring fire damp in mines by means of a variable resonant cavity substantially
in the improved manner herein before described.
In witness whereof, I, the said George Forbes, have hereunto set my hand
and seal, this Tenth day of February, in the year of our Lord One thousand
eight hundred and eighty.