CONTROLEUR DE DEBIT DE GAZ DANS UN TUBE D'ESSAI

TEST-TUBE THROTTLE

Abrégé anglais

ABSTRACT
The invention describes a test-tube for the quantitative
measurement of very small concentrations of gas components with a
reagent strip impregnated with chemical reagents. Arranged before
the reagent strip in the direction of flow of the test gas, is a
flow throttling element. By means of this arrangement, the test
air, which is passed through the test-tube by an air feed pump, has
its forward motion throttled to such an extent that the test air
flows slowly past the sensitive reagent strip producing a change of
colour in zones.

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows.
1. A test-tube for the quantitative measurement of
minimal concentrations of gas components with a test strip
impregnated with chemical reagents, a gas permeable,
flow-throttling holding element arranged in front of this test
strip in the flow through direction, wherein the
flow-throttling element is a fine-grained layer of a chemically
inert material which has a substantially uniform grain size.
2. A test-tube according to claim 1, characterized in
that the grains in the flow-throttling layer are spherical.
3. A test-tube according to claim 1, characterized in
that a granular reaction layer is applied to the flow
throttling element and to the reagent strip.
4. A test-tube according to claim 3, characterized in
that the reaction layer is impregnated with a reagent for
converting the polluting component to be determined into an
easily detectable chemical sequential product.
5. A test-tube according to claim 4, characterized in
that the reaction layer is impregnated with a reagent which
reacts with an unwanted accompanying substance and filters it
out,
6. A test-tube according to claim 1, characterized in
that the reagent strip is made from an impregnated absorbent
material.
7. A test-tube according to claim 1, characterized in
that the reagent strip is made from a nonabsorbent material to
which is applied a layer of an absorbent, finely granular
material which has been impregnated in a suitable manner.
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8. A test-tube according to claim 1, characterized in
that one end of the reagent strip is laid around a gas
permeable mounting element in order to secure the said strip in
the test tube in the longitudinal direction thereof.
9. A test-tube for the quantitative measurement of
minimal concentrations of gas components with a test strip
impregnated with chemical reagents, a gas permeable,
flow-throttling holding element arranged in front of this test
strip in the flow through direction, wherein the
flow-throttling element is a capillary tube which is located in
the testing tube in a close fitting relationship.
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Description

il3~3
The invention relates to a test-tube for quantitative
measurement of very small concentrations of gas components with
a reagent strip impregnated with chemical reagents.
In the case of a known test-tube of this kind, the
reagent strip, impregnated with a detecting reagent, is held to
the inner wall of the test-tube with a granular filler material
(German OS 32 36 792). It is to be regarded as a disadvantage
that, as a result of fluctuations in grain-size and packing
density, the granular filler material may cause flows of test
gas which differ widely locally. This may lead to
irregularities, and thus to inaccuracies in the display
provided by the highly sensitive reagent strip. In addition to
this, there is the danger that dust may be formed during the
filling and application of the granular filler material. If
any of this dust is deposited onto the reagent strip, it can
also cause trouble and lead to incorrect indications.
It is therefore the purpose of the invention to
provide a test-tube with which very small concentrations of gas
components may be measured and may be detected with great
accuracy with a sensitive reagent strip.
According to one aspect of the present invention,
there is provided a test-tube for the quantitative measurement
of minimal concentrations of gas components with a test strip
impregnated with chemical reagents, a gas permeable,
flow-throttling holding element arranged in front of this test
strip in the flow through direction, wherein the
flow throttling element is a fine-grained layer of a chemically
ne/~t
material which has a substantially uniform grain size.
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332~
The advantages obtained with the invention are, in
particular, that the test air delivered through the test-tube
by the feed pump has its forward motion throttled or reduced,
before ~
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3..~ .323
, .
reaching the reagent strip, to such an extent that it flows slowly
and uniformly past the said strip, thus ensuring a clearly
determinable display.
An example of embodiment is illustrated in the drawing
attached hereto and is explained hereinafter in greater detail. In
the said drawing:
Figure 1 is a longitudinal section through a test-tube with a
reagent strip and a flow throttle according to the invention; and
Figure 2 is a longitudinal section through a test-tube with a
reagent strip and another design of flow throttle according to the
invention.
As may be seen from 1 and 2, glass test-tube 1 comprises
molten ends 2 and 3. In the direc-tion of flow 4 of the test air, the
following components are arranged in the said test-tube.
A mounting component 5 which is permeable to the test air, a
flow throttle 6 in the form of a layer finely granular, chemically
inert material (Fig. 1), or a flow throttle 6a in the form of a
capillary tube (Fig. 2), a gas permeable mounting component 7, a
granular sorption - or reaction layer 8, a gas permeable mounting
component 9, a gas permeable mounting component 10 which secures a
reagent strip 11 in the longitudinal direction of the test-tube 1
and, finally a further gas permeable mounting component 12.
The gas permeable mounting components 5, 7, 9 and 12 consist
of a synthetic material, glass, ceramic or metal.
Reagent strip 11 contains a detecting reagent for the
constituent in the air or gas under investigation to be determined,
the detection reaction producing a change in colour. In this

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DS11-4361-5
connection, reaqent. str;p 11 is made oF an ahsorbent mater;a]., for
example, paper, cardboard or t.extile which is impregnated with the
detect;.ng reaqent.
However, the said reagent strip 11 may al.so consist of a
non-absorbent carri.er, for example, a synthetic material or metal,
to which ;.s appl;.ed a layer of fi.nely qranu].ar absorbent material
suitably impregnated with the detecting reagent.
~ ccord;.nq to Figure 1, flow throttle 6 arranged beEore
reagent strip ll, ;.s a finely granuJ.ar layer of chemically inert
material, preferably of uniform grain size, for example, spheres of
equal size~ This produces a definite flow resistance and thus
uniform distribution of the flow of test qas. This layer acts as a
so-called flow throttle. It serves to throttle, or slow down the
forward mot;.on t.o the test air, passed through t.he test-tube by the
feed pump, to such an extent that the said test air flows slowly
past the reagent strip. This allows the sensitive reaqent strip to
be d;..scoloured in zones and ensures a clear]y determinable display.
In Fiqure 2, flow throttle fia is in the form of a capillary
tube inserted into the qlass tube with its edges sealed, with a
spec;fic openinq and lenqth. The effect of this is similar to that
of layer 6 described above in connection with Fiqure 1 If, for the
purpose of direct determination oF the gas to be measured, no
suitable reagent is availab].e for the test-tube procedure, but a
su;.table reagent is availab~e for an eas;.ly determinable sequential
product, then it is advantageous to incorporate, after throt-tling
layer 6 according to Figure 1, or after capillary tube 6a according

to Figure 2, the granular sorption - or reaction layer 8 which is
impregnated with a reagent for converting an easily determinable
chemical sequential product.
If unwanted accompanying substances in the test gas to be
measured falsify the results, but the gas component to be determined
reacts directly with reagent strip 11, sorption - and reaction layer
8 may act as a filter to hold back these unwanted accompanying
substances selectively. In this case, layer 8 is also impregnated
with a reagent which reacts with the accompanying substance and
filters it out. In the form of a preliminary layer in ~ront of
reagent strip 11, layer 8, suitably impregnated, may serve as a
filter, and as a conversion layer, for a new chemical sequential
product, if this is necessary.
In order to take a measurement, ends 2 and 3 of the test-tube
are broken off and test air is drawn through the open test-tube in
the direction of arrow 4, by means of an air feed pump. These test
air flows firs-t through flow throttling layer 6 (Fig. 1) or capillary
tube 6a (Fig. 2), then through sorption - and reaction layer 8, after
which it flows uniformly past reagent strip 11. In the presence of a
substance to be detected, this allows sensitive reaction strip 11 to
be discoloured in zones.
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