An Improved Method of and Apparatus for Detecting and Measuring the Presence and Amount of Inflammable Gases or Vapours Mixed with Air.
Year: 1894

page_text: Date of Application, 14th Aug., 1894-Accepted, 15th Sept., 1894
COMPLETE SPECIFICATION.
An Improved Method of and Apparatus for Detecting and
Measuring the Presence and Amount of Inflammable Gases
or Vapours Mixed with Air.
I, BENJAMIN CHEW TILGHMAN, Jr., residing at 2210, St. James Street, in
the City and County of Philadelphia, in the State of Pennsylvania, one of the
United States of America, Chemist, do hereby declare the nature of this inven
tion and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement:-
My invention relates to an improvement in the method and apparatus for
detecting the presence and measuring the amount of inflammable gases or vapours
contained in the air of mines, oil tanks, and similar places where such gases are
apt to occur. It is well known that if a thin wire or strip of metal be arranged
so as to be heated to a suitable temperature by proper means, as by an electric
current of suitable quantity passing through the strip, that if there are any.
inflammable gases or vapours in the air surrounding the wire so heated, that
these inflammable gases will be burned on the surface of the heated wire; and
the wire will consequently be heated by the burning of the inflammable gases.
and the passage of the electric current to a higher temperature than the passing
of the electric current alone would effect. This increase in heat in the wire due to
the burning of the inflammable gases has a fixed relation to the amount of gas
present in the surrounding atmosphere and burned on the surface of the wire or
metal strip. It is also well known that certain metallic conductors, as, for instance,
platinum, increase their electrical resistance on an increase of temperature, and in
a fixed ratio to this increase of temperature. Therefore, by, properly arranging. a
circuit, including a suitable wire or strip of metal, so that it will be carried into a
place or places where the condition of the air is to be tested, passing a suitable
current of electricity through it and measuring the increase of resistance due to
inflammable gas, if any occurs, over the normal resistance of the current due to the
passage of the electric current alone, the amount of inflammable gases can be
ascertained and that too without the necessity of the observer going to the place to
be tested, which might be dangerous to do, and by this process also the indications
given are positive and do not in any way depend upon the judgment of the person
making the test, but on a properly constructed instrument may be read off in
per cents. of inflammable gas in the air.
My invention consists in an apparatus and method of operation designed to
accomplish this end, also in a special form of galvanometer designed to be used in
connection therewith, and also in an arrangement of the apparatus so that it my
be compact and portable.
My invention is illustrated in the acompanying drawings, in which,
Figure 1 is a diagrammatic view showing a convenient mode of arranging the
apparatus in a mine shaft.
Figure 2 is a diagram of a modified form of determining apparatus.
Figure 3 is a diagram illustrating another form of determining apparatus.
Figure 4 is a section of the casing designed to protect the testing spiral.
Figure 5 is a side view, partly in section, of a portable arrangement of my
testing apparatus.
Figure 6 is a plan view of a differential galvanometer specially designed for
quick measurements.
Figure 7 is a side view of the galvanometer, showing the arrangement of the
lower electro-magnet, and
Figure 8 is a diagrammatic view showing the windings of the magnet,
::

page_text: M represents the shaft of a mine, and A' and A2 places where it is desired to test
the presence of inflammable gases; is a station at any suitable place, as at the
mouth of the shaft, where it is desired to observe and record the condition of the
air at the different testing stations in the mine. B is a suitable source of electrical
supply, here shown as a battery, a a line wire, and a¹ a return wires from the
stations AA respectively. These return wires may conveniently end at contact
points as and a key as K is preferably so arranged that any one of the circuits
may be closed at pleasure. A suitable indicator I is arranged in circuit, preferably
at the station M and near to the key K, which shows at any desired distance from
a testing station A¹ or A2 étc., the resistance in the circuit due to the heating of
a metal strip introduced therein at the testing stations, and so the amount of
imflammable gases at said stations.
Before describing the details of the apparatus and the various means which may
be used to indicate the amount of resistance in the circuit, I would remark that the
substance introduced into the circuit at the testing station should have an
appreciable resistance in relation to the rest of the circuit, so that the variations of
resistance under the different percentages of gases or vapours may be measured
without the use of instruments of excessive refinement, and the most convenient
substance I have contemplated using is a thin wire of platinum preferably wound
in a spiral to present as much surface as possible to the air. The current to be
used may be such as will heat the platinum spirals to a temperature at which they
will be just below visible redness in the dark, though I have found that if the
current used is much stronger, so that the spirals will glow brightly, that the
increase in resistance under the same proportions of gas or vapour in the air will be
practically the same as when less strength of current is used; I prefer, however,
to use a current which will heat the spiral to such a temperature as will cause it to
be barely luminous in diffused daylight. The increase in temperature of the spiral
over that induced by the current is due, as has been said, to the amount of
inflammable gas burned on its surface, but if there is a current of comparatively
cool air flowing quickly over the surface of the heated spiral the temperature of the
spiral falls, about proportionally, to the quickness of the current of air in which
the testing wire is situated. The effect of an unduly quick current is therefore to
show apparently less inflammable gas present in the air of this current than really
exists therein. In order to avoid having the indications affected in this way I
prefer to enclose the spiral in a casing so constructed that while a perfectly free
access of air is permitted to the testing spiral, a draft of air in the shaft in which
the spiral is placed will have no effect on it.
Returning now to the drawings, A, Figure 4. represents a casing in which the
spiral S of platinum wire is enclosed and it may conveniently be constructed as
shown, where it consists of a box preferably long in comparison to its width and
breadth and conveniently made of metal. At their lower end is a cover partly
closing the bottom of the box but having an opening d preferably arranged with
inclined edges as shown. At about the centre of the box or casing I arrange a
spiral S of suitable metal, as explained, preferably surrounding it with some
refractory substance which is not a good conductor of heat or electricity, such as
fire-brick or asbestos. This is preferably arranged as a block 2, as shown, having
a hole therein, which forms a flue or chimney so that all the air going through
the casing will pass close to the spiral. At the top of the casing is arranged a
cover with holes therein and a sloping roof as is preferably arranged over
the whole and acts with the cover as baffles to prevent any outside draft from
having effect on the spiral within the casing. The spiral however, when heated.
heats the air surrounding it which, rising, creates a draft in the casing A and so
furnishes continually a fresh supply of air to act on the spiral, which supply is
dependent on the heat of the spiral and independent of any draft in the mine
shaft.
In order to prevent the ignited gases from setting fire to or exploding the
inflammable gases in the surrounding atmosphere, sheets of gauze F F¹ as many as

page_text: are deemed necessary are placed above and below the spiral many convenient
manner.
For measuring the resistance of the circuit any proper instrument may be used.
For the measurement of the resistance in circuits where the air to be tested is at
any considerable distance from the place at which the indications are read, the
Wheatstone's bridge method I consider preferable; in this, as shown at W,
Figure 1, a suitable comparing resistance being introduced as at the variations
in the main circuit can be easily read off by proper manipulation of the instrument.
A rheostat R, as shown in Figure 2. may also be used and resistance added or
subtracted till the resistance in the circuit """ balances that in the main circuit,
as will be seen from an ordinary galvanometer G'connected to the two circuits by
short wires as gg. Any proper means for measuring resistance may of course be
used, and I do not wish to be considered as limiting myself to any particular
means shown.
In cases where a fixed resistance is used against that of the testing wire or strip,
said fixed resistance being practically unchanged by the current flowing through it,
then the connection with the indicating instrument should not be made until such
time as the testing wire or strip has attained a steady temperature, and therefore a
steady electrical resistance under the joint effects of the testing current and
whatever inflammable gases or vapour may be present in the air being tested. By
making the testing wire or strip very thin and light so as to expose a large amount
of surface in proportion to its bulk, it will attain a steady temperature in less time
than if otherwise constructed, but in many cases, particularly when quickness of
manipulation is desired, I prefer to use as a balancing resistance a coil or strip
similar to the testing coil or spiral except that the balancing coil is surrounded by
an atmosphere free from any inflammable gases, this may be introduced in the
resistance as shown in Figure 1, or arranged. as shown in Figure 3. In this case
no account need be taken of the time in which the testing circuit is heating up, and
thus attaining a constant resistance, as the two circuits heat up concurrently. This
arrangement is shown diagrammatically in Figure and is preferably used in the
portable apparatus described hereafter. A Figure 3, being a housing containing
a spiral S similar to those used in the stations A' A² etc., arranged on a circuit at all
and a galvanometer is arranged to indicate the relative amount of current in the
two circuits a⁰ a¹ and a a², and keys are arranged in any convenient manner to
close the line circuits and the testing circuit at will..
It is of course obvious that while I have shown but two testing stations A¹ A²
that any number may be arranged on the line wire a.
In connection with the portable apparatus above referred to I prefer to use a
particular form of galvanometer wound in a manner to be hereafter explained,
which is particularly adapted for rough work and is not disturbed by a small
amount of jostling and is arranged to give quick readings.
This portable instrument is shown in Figure 5 where B is a source of electricity
which may be a battery or small hand dynamo, or any other proper arrangement
to generate a current, and cel are binding screws on the plus and minus poles
thereof respectively: 23 being proper binding screws on the outside of the
carrying case N.
From the battery or source of electricity two electrical circuits are led, one,
indicated in dot and dash lines from the binding screw e to
a galvanometer G¹
entering at e then through the galvanometer in a manner to be explained, out at e,
through circuits a a¹, including the spiral S. and when the key is depressed, back to
the minus pole c', completing the circuit. The other circuit, indicated in full lines,
passes in similar fashion from the binding screw through the galvanometer,
entering at and emerging at e² to the spiral S¹ and when the key K' is depressed,
back to the minus pole completing the circuit. The key K' is preferably
arranged as shown so that both circuits can close simultaneously. The spiral S is
arranged in this form of instrument on the end of a pole T so that it can be poked
into corners where inflammable gases are supposed to occur, and is, of course,

page_text: suitably covered by gauze and protected by guards t. The galvanometer G¹ is
arranged with a needle g preferably pivoted on a stretched fibre g³ and covered
by glass plates ; an index plate g is arranged as usual and by the amount of
deflection of the needle the amount of inflammable gas can be ascertained. The
galvanometer G₁ and spiral St may be arranged as shown so that the light from the
spiral S will fall on the dial of the galvanometer to assist reading in dark places.
These instrumentalities are all arranged in a portable box or carrying case N so as
to be conveniently carried wherever desired. The most convenient form of
apparatus has been shown in Figure 5. but obviously any other proper indicator
could be substituted for the indicator shown.
The galvanometer I prefer to use consists of two electromagnets, each wound with
two circuits in such a manner that when the amount of current in each is equal or
when one current bears any other fixed and predetermined relation to the other, one
of these electromagnets will be freely excited, and the other will be entirely
unexcited but when the currents in the two circuits vary from this fixed and
predetermined ratio, then the excited magnet begins to lose a portion of its
excitement while the previously unexcited magnet begins to get excited; and when
the circuit in one branch ceases entirely, then the previously excited magnet loses
all its excitement, and the previously unexcited magnet becomes fully excited. A
galvanometer acting in this manner is shown in Figures 6, 7 and 8, where P is a
continuous bar of soft iron constituting a closed magnet circuit carrying exciting
spools P1 P2 P3 P+ of which P P are traversed by one current, and P2 P+ by the
other, and which are wound in such a manner that their magnetic effect is opposed
to each other and wound with such a number of turns, that at the predetermined
ratio of the two currents traversing them their magnetizing effect shall be equal.
The effect of their being traversed by such currents will be the formation of
consequent poles between the magnetizing spools. The other electro magnet R³
which is of the ordinary horse shoe type and preferably fitted with pole pieces
is placed so that its poles are on the same horizontal plane as the consequent poles
of the first magnet, but at an angle, preferably a right angle, to the line joining the
same. The exciting spools R' Re of this magnet are one or both wound with both
circuits intimately interlaced with each other and the number of turns on each is in
the ratio determined as above, so that when the two currents have that ratio the
magnet is unexcited.
2
A magnet needle as g¹, preferably hung on a stretched fibre is arranged to
swing hetween the magnets. The effect of which construction is that when the
current flowing in the two circuits is of the predetermined ratio the needle will
point in the direction of a line joining the poles and when the current flows
only in one circuit it will point in the direction of a line joining the poles 12 of
the other magnet and when it flows in both circuits in a relation different from the
predetermined one, the needle will point in a direction intermediate to the two
and at an angle proportional to the difference between the two currents. The
advantage of this form of construction consists in the fact that the needle may be
made very light and be made to move in a very strong field without external
control, and it may therefore be made dead beat and also being to a great extent
shielded is to that extent insensible to the external field in which the instrument
may be placed. By having the needle suspended by a stretched fibre it is to a
great extent independent of the position in which it is placed and even of such a
slight degree of motion while giving indications as would be experienced by an
instrument held in that hand.
By arranging the system as shown in Figure 1 that is, by having one line wire
(as ) running to all the stations and a return wire from each; or a common return
wire and a separate line wire to each nearly half the wire needed can be saved.
As shown in Figures 3 and 6, it is possible by arranging contact points as fat
the point on the dial * corresponding to the danger point and arranging a contact
maker as 3 on the needle and putting an alarm in a circuit whose terminals are
the points 12 an alarm may be given when the danger point is reached,

page_text: It is also obviously possible by suitable means, as by the reflection of a ray of
light upon a moving sensitized surface, the movement of said ray of light
being controlled by the apparatus as by a mirror fixed to the galvanometer or any
other moving index, to obtain and preserve a continuous record of the condition of
the air at any point as desired, the arrangement of instruments to obtain such
result being of course perfectly apparent.
The operation of the apparatus is believed to be clearly understood from the
foregoing description, the observer having put any desired station in circuit by
means of the contact key the spiral becomes heated and heats the surrounding
air causing an upward current in the casing A, this draws in air containing gases,
if any such are present, and the required indication is given at the observing
station M.
It may be here noted that if the inflammable gases or vapours are present in
very large percentage in the air being tested, so as to be incapable of either
exploding or supporting combustion their thermal capacity being relatively greater
than air, the testing wire immersed in such an atmosphere will attain a lower final
temperature under the influence of a given current of electricity than if immersed
in a
current of pure air. The effect is to give a backward indication or one
in a contrary direction to that given by an appreciable quantity of gas. This
however, does not confuse an observer as such change occurs quite suddenly at
percentages immediately higher than those which give the maximum forward
deflection.
It will be noticed that where I use the words independent indicator' in the
claims, I mean an indicator independent of the testing spiral.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim, is
1. In an apparatus for detecting the presence and amount of inflammable gases
and vapour in air, the combination of a source of electrical supply, a circuit
connected with the source of the electrical supply, a conductor of relatively high
resistance arranged in said circuit and adapted to change its resistance under the
influence of the electric current and any inflammable gas or vapour in the air,
and an independent indicator for showing such changes of resistance.
2. In an apparatus for detecting the presence and amount of inflammable gases
and vapours in air, the combination of a source of electrical supply, a circuit
connected with the source of electrical supply, a conductor of relatively high
resistance arranged in said circuit and adapted to change its resistance under the
influence of the electric current and any inflammable gas or vapour in the air, a
second circuit over which a current of electricity is also passed, and means for
comparing the resistances of the two circuits.
3. In an apparatus for detecting the presence and amount of inflammable gas or
vapour mixed with air, the combination of a source of electrical supply, a circuit
connected with the source of electrical supply, a conductor of relatively high
resistance arranged in said circuit and adapted to change its resistance under the
influence of the electric current and any inflammable gas or vapour in the air, a
second circuit over which a current of electricity also passes. al rheostat for
changing the resistance of this second circuit, and a galvanometer situated in a
bridge connecting the two circuits substantially as and for the purpose specified.
4. In an apparatus for detecting the presence and amount of inflammable gases
and vapours mixed with the air, the combination of a source of electrical supply,
a circuit connected with the source of electrical supply, a conductor of relatively
high resistance arranged in said circuit and adapted to change its resistance under
the influence of the electrical current and any inflammable gas or vapour in the
surrounding air, a second circuit over which in normal conditions is passed a current
of electricity equal to that which is passed over the first named circuit, and means
for comparing the resistances of the circuits when their equality is disturbed,

page_text: 5. In an apparatus for detecting the presence and amount of inflammable gas or
vapour mixed with the air, the combination with a source of electrical supply, of
a circuit connected to said source of electrical supply, a coil of wire, as S. arranged
in a substantially vertical position, said coil having a relatively high resistance,
and arranged so as to be open to the air to be tested, and adapted to change its
resistance under the influence of the electric current and the presence of the
inflammable gas or vapour, and an independent indicator arranged in the circuit and
adapted to show the changes in the resistance thereof.
6. In an apparatus of the class described, the combination with a source of
electrical supply, of a circuit connected with the source of electrical supply, a
conductor of relatively high resistance arranged in said circuit, a casing arranged
to protect this conductor from extraneous drafts and an independent indicator
adapted to be arranged in the circuit and to show variations of resistance therein
under the influence of any inflammable gas or vapour in the air surrounding the
aforesaid conductor.
7. In an apparatus of the class described the combination with a source of
electrical supply, of a circuit connected with the source of electrical supply, a
conductor of relatively high resistance, as spiral $, arranged in said circuit, a
chimney with non-conducting walls enclosing said spiral and an independent indicator
substantially as and for the purpose specified.
source of
8. In an apparatus of the class described, the combination with a
electrical supply, of a circuit connected with the source of electrical supply, a
conductor of relatively high resistance, as spiral S. arranged in said circuit, a
chimney with non-conducting walls enclosing said spiral, a casing arranged to
protect the spiral from extraneous drafts, and an independent indicator, substantially
as and for the purpose specified.
source of
9. In an apparatus of the class described. the combination of a
electrical supply, a circuit connected therewith, a conductor, as S. of relatively
high resistance inserted in said circuit, a box or chest surrounding said conductor a
chimney surrounding the spiral, and wire gauze enclosing the conductor S on
either side so that gases or vapours heated between the sheets of gauze may not
inflame the surrounding gas or vapour.
10. In an apparatus of the class described, a source of electrical supply in
combination with a line wire leading from such source of electrical supply, a series
of conductors of high resistance connected to said line wire, a series of return wires
adapted to complete the circuit, one connected to each said conductor of high
resistance, an indicator, and means adapted to complete the circuit through each
wire and said indicator at will.
11. In an apparatus of the character described, a source of electrical supply, a
conductor of relatively high resistance inserted in said circuit, which conductor is
adapted to change its resistance under the influence of the electric current and
inflammable gas and vapour, and an independent electrical testing instrument to
indicate the changes in the resistance in combination with a portable box as N in
which the above mentioned instrumentalities are arranged.
12. In an instrument of the character described, a source of electrical supply, a
circuit as a a connected therewith and having a conductor of relatively high
resistance inserted in said circuit, a second circuit as a all through which a current
of electricity also passes, in combination with a galvanometer having cores around
which the currents in the circuits a a¹ and a¹ all pass, forming two electro-magnets
which are wound in such a manner that when the amount of current in one circuit
is equal or bears a certain relation to the amount of current in the other one of
these magnets will be excited to its maximum degree and the other will be unexcited,
while if the relative amount of current in the two circuits varies from this
predetermined ratio the previously excited magnet becomes less excited and the
magnet which was not excited becomes so, and also having a needle acted upon by
said electro magnets and adapted to indicate the variations in the intensities of
the currents in the two circuits,

page_text: 13. In an instrument of the character described, the combination of a source of
electrical supply, a circuit as a a' connected therewith having a coil S of relatively
high resistance inserted therein, a second circuit as a all, a spiral S¹ inserted
therein, a galvanometer G' connected with the two circuits and adapted to show
the differences in resistance therein, the coil S¹ and galvanometer being so arranged
relatively to each other that the light from the spiral will be thrown on the dial of
the galvanometer.
14. The method of detecting the presence and amount of inflammable gas and
vapour mixed with air which consists in passing two currents of electricity, one
through a circuit in which is inserted a conductor adapted to change its resistance
under the influence of the current of electricity and the presence of inflammable
gas or vapour and the other current through a circuit not influenced by the
inflammable gas or vapours, and comparing the resistance of the two circuits.
15. The method of detecting the presence and amount of air or inflammable gas
or vapour present in the air which consists in passing a current of electricity
through a circuit including a conductor of relatively high resistance and so heating
the conductor causing a current of air to flow around said heated conductor by the
heat of the conductor itself and measuring the difference of resistance in the circuit
due to the presence of any inflammable gas or vapour in the air rising round the
conductor substantially as described.
Dated this 14th day of August 1894
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.