Note: Descriptions are shown in the official language in which they were submitted.
912,283
1066141
METHOD AND DEVICE FOR MONITORING VAPOR
CONCENTRATION AT A PHASE INTERFACE
The present invention relates to a method and
device for monitoring and indicating the concentration
of a selected vapor component at a phase interfaceO
The measured concentration is related to a parametric
concentration of the vapor and the concentration of vapor
relative to the parametric concentration is indicated.
In a preferred embodiment, the present invention
relates to a method and device for continuously monitoring
and indicating concentrations of volatile components, eOgO
moisture, in soilO The method comprises sampling selected
vapors present at the surface of the soil, comparing the
vapor concentration in the sample with a standard, and
indicating the concentration of a corresponding volatile
component in the soil.
Monitoring devices are disclosed which perform
the described functions The monitoring devices comprise
sensing and comparing means enclosed within a moisture-
impermeable, vapor-permeable envelopeO The disclosed
devices are adapted to be located at a phase interface
from which a vapor is issuing and can effectively sample
and indicate the concentration of various selected vapors
at the interface~ This concentration can then be compared
to a standard representative of some parametric concentra-
tion of the vapor which can be related to the concentra-
tion of a corresponding unvaporized volatile componentfrom which the vapor issues, a chemical reactant or
agent causing formation of the vapor or the likeO The
concentration of the vapor relative to the standard is
indicated by the device such as by a visible color changeO
1 - ~k5
~066141
The method and monitorlng devices dlsclosed
herein can be used to particular advantage for monitor-
ing the moisture available to potted plants and can
visibly indicate the point at which the soils containing
the plants should be wateredO Alternatively, the method
and devices can be used to monitor the concentration of
other volatile components, such as ammonia, in soil and
visibly indicate their concentrationO The devices can
also be used to indicate the presence of moisture in
diapers, surgical dressings, or the like, as will be
described in greater detail hereinafterO
Devices for monitoring the moisture content
of the soil around potted plants are known~ These
devices generally employ a wick with a color indicator
associated therewith which indicates the presence of
moisture in the wick when the wick is submerged in the
soil near the plant. A change in color indicates the
need to water the soil. U~S. Patents 3,019,638 and
3,702,755 exemplify devices of this typeO
These wick-type devices do not operate satis-
factorily under certain conditions. In some cases the
construction of these devices causes the wick to dry
prematurely by evaporation and the device does not
reflect the actual status of the soil's moisture condi-
tion. Furthermore, wicks tend to concentrate water
soluble materials wlthin their structure and thereby
become less transmissive, particularly the portion
above the soil's surface where the wicks can dry out
and actually become hydrophobic and inoperative due
to the build-up of these water soluble residuesQ These
~066141
phenomena can produce lnaccurate readlngs whlch may
cause the plant to be watered more often than necessa~y,
resultir.~ i~ plant damageO Cellulosic wlcks tend to
degrade ~ithin a short time and may requlre replacement
of these indicating devices rather frequentlyO
U.SO Patent 3!788,128 discloses a devlce for
determining the moisture content of soil at a dlstance
~elow the surface of the soilO The device is adapted
to be submerged in the soil and contains one or more
lndicating members adjacent a cavity within the devi~e
and separated therefrom by a membrane which is permeable
to moisture but not to liquid waterO The cavity
communicates with the soil through water vapor permeable
passagesO The indicating members change color in
response to a specific humidity range in the cavityO
By determining the temperature and the amount of humldity
- in the subsoil, the device aids in determining the optimum
concentration of seed to be sownO
UOSO Patent 3,680,364 dlscloses a humidity
.monitoring device for-curing concreteO The devi~e
comprises a chamber having a base member and a viewing
cover and containing therewithin a humidity indicating
element.O The base.portion of the chamber is permeable
to moisture, while the remainder of the chamber is
impermeable to moisture The device ls placed on the
surface of, or is pressed into the surface of, curing
conGrete and visibly indicates, by a color change, when
the concrete requires watering for proper hydratlonO
UOSO Patent 3,oo4j895 discloses a deYice fo~
absorbing large quantities of ammoniaO The abscrb~ng
~()66~41
agent is enclosed within a liquid impermeable, ammonia permeable envelope.
An indicating material is included in the envelope which changes color when
the absorbing agent is depleted.
According to the present invention a relatively simple, but
effective, method and device are provided for monitoring and indicating the
concentration of vapor at a phase interface such as a solid/gas, liquid/gas
or even a gas/gas interface, the device itself being preferably located in
the gas phase which is not the source of the vapor and which is usually air.
The method comprises (a) continuously collecting a representative vapor
sample in a differentially vapor permeable, liquid impermeable, envelope
directly from a vapor source phase at the phase interface, said envelope
comprising a base and a cover vapor permeable, said cover having a vapor
transmission rate equivalent to a water vapor transmission rate of between
20 and 60 grams/1000 cm2/24 hours; (b) comparing the concentration of a
selected vapor component in said sample with a standard contained in said
envelope which is representative of a selected parametric concentration of
said vapor in said sample; and (c) visibly indicating the concentration of
said vapor in said sample relative to said standard.
The parametric concentration which is selected can be a vapor con-
centration which is deleterious or advantageous in itself or can be a con-
centration which can be related to a concentration of the vapor inrthe source
phase from which the vapor issues, the concentration of a corresponding
volatile component in the source phase, the concentration of a chemical
reactant or agent which acts to produce the vapor within the source phase
or the like. Thus, the method and device can be used to monitor the moisture
in soil as well as detect and indicate the presence of moisture in diapers,
surgical dressings and other absorbent materials. The invention also has
utility in the detection and indication of vapors other than moisture vapor,
e.g. ammonia, contained in or issuing from soil, water, decomposing
~0~6~41
proteinaceous material or other sources.
According to an aspect of the present invention there is provided
a device for monitoring and indicating the concentration of a vapor at a
phase interface comprising (a) a sensing means for comparing the concentra-
tion of a selected vapor component in a sample with a standard which is
representative of a selected parametric concentration of said vapor in said
sample, said sensing means including means for indicating the concentration
of said vapor in said sample relative to said standard, and (b) a differ-
entially vapor permeable, liquid impermeable envelope enclosing said sensing
means to responsively couple said sensing means to a vapor source phase at
said phase interface, said envelope comprising a base adapted to rest on said
vapor source phase and a cover for said base, said base and said cover vapor
permeable defining a sealed, closely conforming envelope containing said
sensing means, said cover having a vapor transmission rate equivalent to a
water vapor transmission rate of between 20 and 60 grams/1000 cm2/24 hours,
said base having a vapor transmission rate at least 50% greater than the vapor
transmission rate of said cover, said cover adapted for viewing said indicat-
ing means.
Typical sensing and indicating means are materials which change
color or other optical, chemical or electrical properties in response to
exposure to a given concentration of a vapor component, e.g. cobalt chloride
for sensing moisture vapor; alizarin or pH papers for sensing ammonia.
The monitoring device also includes, in combination with the sens-
ing and indicating means, a liquid-impermeable, vapor-permeable envelope
enclosing the sensing means The nevelope comprises a base and a cover
wherein the base is adapted to rest on or otherwise communicate with the
phase from which the vapor issues. The base transmits vapor at a rate
greater than the cover. Preferably the base has a vapor transmission rate at
T -5-
~066~4~
least about 50% greater than the cover and most preferably at least about
100% greater than the cover.
A -5a-
1~)66141
As noted, the base of the device can rest
directly on the vapor source phase or otherwlse be
fastened in contact wlth the vapor source phaseO
Alternatively, the base can be spaced from the source
phase if other means, such as a tube or other connectlng
means, is used to maintain the base in communication
wlth the vapor source phase so that the devlce can
effectively sample the vapor issuing therefromO
The differentially transmissive envelope used
in the device of the present invention is necessary to
effectively obtain representative vapor samples from a
vapor source phaseO Use of the differentially vapor
permeable envelope provides a device which is capable
of sensing and indicating low levels of vapor or slight
or slow changes in the vapor concentration whereas other
devices, not having a differentially vapor permeable
envelope, fail to accurately indicate the levels or
changes of vapor concentration~
In a preferred embodiment of the present
invention, there is provided a method and device for
accurately and continuously monitoring and indlcating
parametric concentrations of selected volatile components
in a soil phaseO For example, the selected parametris
concentration may be the minimum amount of soil moisture
content necessary to keep a potted plant from wiltlng,
or a deleterious concentration of ammonia ln the soil
or some other meaningful concentration~ The devlce
disclosed in the present invention overcomes the
deficiencies of prior art wick-type devices sinse the
device described herein can be used for monitoring soll
-- 6 --
~066~41
moisture without requiring the presence of liquids wi~hln
the device and particularly eliminates the use of wicks
and the problems associated therewithO
The present inventor has discovered that the
concentration of various volatile soil components in the
upper levels of soil, for example the top 30 cm of soil
can be determined by analyzing the vapor released from
the surface of the soil at the air-soil interfaceO The
concentratlons of these vapors can be empirically
correlated with a corresponding concentration of the
volatile components in the soilO These correlations can
be used with the method and devices of the present inven-
tion to indicate selected parametric concentrations of
volatile components in soil, and are particularly useful
in indicating moisture available to shallow-rooted
plants. The correlations for available moisture are use-
ful for various types of soil ranging from heavy clay to
light potting mixO Thus, although plants growing in a
heavy clay may begin to wilt at lower absolute soil
moisture concentrations than those growing in lighter,
more loosely packed soil, the moisture in the soil wh~ch
is effectively available to the plant can be correlated
with the molsture available at the surface ln the form of
water vapor and is substantially independent of the soil
type~
Similarly, a concentratlon of other volatile
components in soil, such as ammonia, can be determined by
measuring the level of the desired vapor componen~ avail-
able at the surface of the soil and correlating this
amount with the amount in the soil~
~:)66141
By choosing an appropr3.ate standard, various
desired parametrlc concentrations of volatlle soil
components can be indicated by the method and devices of
this inventionO Accordingly, one aspect of the present
invention relates to a method for continuously monitoring
the concentration of volatile soil components, particul~rly
water, which comprises (1) sampling directly from the
surface of the soil a representative portion of a selected
vapor component released from the air-soil interface of
the soil to be monitored, (2) comparing the vapor con-
centration in the sample with a standard which is
representative o~ a parametric concentratlon of a corres-
ponding volatile component in the soil, and (3) indicating
the concentration of the vapor in the sample relatlve to
the standard and thereby indicating the concentration of
the corresponding volatile component in the soilO The
method is particularly useful in monitoring available
amounts of moisture and ammonia in soil contain.ing shallow-
rooted plantsO In one embodiment the moisture Yapor risirg
from the surface of the soil around a potted plant i8
sampledO The relative humidity of the moisture vapor is
determined and compared to the relative humidity of
moisture vapor rising from soil having a selected para-
metric concentration of moisture, such as the available
moisture needed to sustain the life of a plantO The
sampling and comparing process is continuous, and when
the moisture vapor concentration in the sample is equal
to or l.ess than the standard concentration, the need for
additional water in the soil is indicated, such as by a
visible color changeO
1066~4~
An aspect of the present invention also relates
to particular devices adapted to rest on the surface of
soil and continuously monitor and indicate the concentra-
tlon of specific volatile components in the sollO The
devices of the present invention include a sensing means
and means for responsively coupllng the sensing means
directly to the,surface of the soil so that a representative
sample of the volatile components released at the air-soil
interface are presented to the sensing meansO The sensing
means is capable of continuously comparing the concentration
of a selected volatile component ln the sample with a
standard which is representative of a parametric
concentration of a corresponding vola~ile component in the
soil, and includes means for indicating the concentration
of the selected volatile component in the soilO In one
embodiment the device comprises in combination a sensing
element overlying a flat baseO A cover sheet having a
viewing means, such as a transparent cover or a cover hav-
ing a transparent window in register with the sensing
element, overlies the sensing elementO The edges of the
cover sheet are ~oined to the base to form an envelope
which closely conforms to the sensing element leaving a
minimum of free space within the envelopeO
The cover sheet and base must be permeable to
vaporous components, but must be impermeable to liquidsO
The vapor transmisæion rate (expressed as vapor weight/unit
area/unit time~ of the base should be greater than the
vapor transmission rate of the cover sheetO
The differentially vapor-pe~meable envelope
formed by the cover sheet and the base, which can rest
_ g _
~0661~L
directly on the soil, serves to responsively couple the
sensing element to the soil surface and is capable of
sampling a representative portion of vapor released from
the surface of the soil corresponding to a selected
volatile soil component.
The sensing element comprises a vapor-
responsive indicating component which is capable of
continuously sensing a vapor sample and providing a
detectable change in property, preferably a visible
change in property such as a change in color, in response
to changes in vapor concentration in the sample relatlve
to a selected standard concentrationO For example, where
soil moisture is being monitored, the standard may be
75% R~H~ ~ which has been found to correlate with a para-
metric concentration representing the plant-life-sustain-
ing available moisture in the soilO When the continuously
monitored sample concentration changes from above to below
the standard (or vise versa) indicating the change from
above to below (or vice versa) a parametric concentration
of moisture in the soil, a visible change in the color of
the sensing element or some other detectable change in
property may be effectedO Thus, a material whlch changes
color or visibly responds to a change in RoH~ at the 75%
level can be used as an effective indicating meansO
Particularly useful as indicating components in
the sensing elements are hydrated salts which change color
in response to given changes in relative humidity or
deliquescent compounds which exhibit a change in color or
other optical properties in response to given changes in
relative humidityO Alternatively, materials which are
-- 10 --
~066~41
sensitive to other vapor components, such as ammonia,
can be used for monltoring varlous soil volatilesO
While for most applications it is preferred
to use a reversible sensing element, iOe one that can
repeatedly change a property, such as color, ln response
to repeated changes in vapor concentration, so that
continuous monitoring can be achleved. However, for
some applications the device can employ a sen~ing element
which undergoes an irreversible change in response to
exposure to a given vapor concentration As noted
previously, the differentially vapor-permeable envelope
used in the monitoring device allows particularly
effective continuous monitoring of subtle changes in
vapor concentration and, accordingly, the use of a
reversible sensing element provides a most advantageous
combination ln accordance with this invention
The devices of the present invention are
placed in intimate contact with the surface of the soil
The device can be used to monitor the concentration of
volatile components in potted soil as well as unpotted
soil and can be successfully used in determining the
moisture andother volatile components available to
potted plants as well as outdoor vegetation, such as
grass or other shallow rooted plants When the device
is adapted to monitor the moisture content of soil,
the device, in one embodiment, exhlbits a given col.or
when there is sufficient available water in the soil to
sustain the life of the plantO When the available
moisture in the soil approaches a selected parametric
concentratlon, such as when the available moisture is
-- 11 --
J
r
1066141
lnsufficlent to malntaln the health of the plant, the
indicating element changes color to warn that the soll
surrounding the plant needs wateringO When sufficient
water has been added, the indicatlng element resume~ lts
former color until the moisture concentration in the
soil again approaches the parametric concentrationc
Different parametric concentrations can be indicated by
employing various indicating elements which change color
at characterlstic vapor concentratlonsO
The lnvention can be further illustrated by
reference to the specific embodiments shown in the
drawings wherein:
FIGURE 1 is a perspective view partlally in
cross section of a monitoring device according to the
present invention;
FIGURE 2 is a perspective view of an alternate
embodiment of the disclosed monltorlng device,
FIGURE 3 is a cross section along line 3-3 of
the monitoring device shown in FIGURE 2;
FIGURE 4 ls a perspective view of a potted
plant showing a monitoring device such as that shown in
FIGURE 3 positioned on the soll in close proximity to the
plantO
FIGURE 1 shows one embodiment of a vapor monitor-
ing device 10 comprising a sensing element 16 enclosed in
a closely conforming envelope which comprises base 12 and
cover 140 Base 12 is permeable to vapor, but ls lmpermeable
to soil and other solid or llquid components which may be
presentO Cover 14 is shown in FIGURE 1 as being coe~tensi~e
3G with base 12 and is ~oined to base 12 at the common
1066141
periphery of base 12 and cover 14~ The base 12 and
cover 14 can be ~oined by conventional means such as by
heat seallng or by the use of adhesivesO Cover 14 is
permeable to vapor, but is impermeable to bulk liquids
or solidsO
While base 12 and cover 14 are both permeable
to vapor, cover 14 has a maximum vapor transmission rate
which is less than the vapor transmission rate of base 12
so that the envelope formed by base 12 and cover 14 is
differentially vapor permeableO The vapor transmission
rate of the base would ideally be infinitely higher than
the cover. The vapor transmlssion rate of the base should
be at least 50% greater than that of the cover and prefer-
ably at least about lO0~ greater than that of the coverO
The minimum vapor transmission rate of the cover
should be sufficient to allow a reasonably quick response
timeO Generally the response time for the monitoring
device should be about 15 minutes or lessO For example,
for monitoring moisture vapor issuing from soil, the
minimum rate of water Yapor transmission (WVT) of cover 14
should be about 2 g/1000 cm2/24 hours, and the maximum WVT
can be as high as about 60 g/lO00 cm2/24 hoursO Preferably
cover 14 has a WVT in the range of about 20 to 40
g/lO00 cm2/24 hoursO Base 12 must have a minimum WVT of
at least about 3g/lO00 cm2/24 hours, and preferably at
least about 40 g/lO00 cm2/24 hoursO Corresponding rates
can be readily determined for monitoring other vaporsO
Cover 14 should be transparent or be provided
with other means for observing sensing element 16 such as
a window in register with senslng element 16~
1066~41
Sensing element 16 includes an indicatlng
component which provides a detectable change in property
in response to given changes in the vapor concentration
within the envelope, such as a vislble change in color,
and will be described in greater detail hereinafterO
As noted previously3 base 12 must be permeable
to vapor and impermeable to bulk liquids or solidsO
Materials which meet this requirement are vapor permeable
or microporous polymeric films or alternatively hydro-
phobic porous pads, such as an oil-absorbent, polypropylene
microfiber matO These microfiber mats are known in the
art as exemplified in U~S0 Patent 3,847,821 (Column 5)0
The vapor permeable films which can be used for base 12
or cover 14 are well known in the artO Polymeric materials
such as cellulose polymers and copolymers, polyesters,
polyethers, polyurethanes, polyalkylenes, polyacetates and
the like which have the required vapor transmission
properties can be usedO Microporous polyester and poly
ether urethanes can also be usedO Cellulose acetate is
particularly preferred as a cover material for devices
monitoring moisture vaporO As noted previously, these
materials should not transmit bulk water, and therefcre
excessively hydrophilic polymers such as hydrophilic
polyoxyethylene polyurethane polymers should not be used
in the devices of this inventionO
The aforementioned characteristiGs of base 12
are critical to the successful operation of device lOo
If base 12 is permeable to liquid water or is constructed
so as to wick water into contact wlth sensing eleme~t 16,
the de~ice will provide erronecus indications due to ~he
- 14 -
1066~41
presence of the liquid water in contact with the sens.ing
elementO In addition, the liqu'Ld water may ~end t~ leach
indicating component from sensing element 16, shortenlng
the useful life of the monltoring device lOo Thus 3 base
12 is not a wick material as used in prior art devices,
and in fact must be hydrophobic or otherwise impermeable
to bulk liquid for the device of the present invention
to operate successfullyO The liquid impermeability of
device 10 is particularly advantageous when the monit~r-
ing device is to be used for potted plants, wherein thedevice may be sub~ected to periodic floodlng during
watering of the plant~
As shown in FIGURE 1, cover 14 should closely
conform to the sensing element 16 so as to minimize the
free space in the envelope defined by cover 14 and base 120
Mi~imizing the free space helps to prevent condensation of
moisture within the envelopeO
Sensing element 16 includes an indicating
component which alone, or in comblnation with other
portlons o~ the senslng element, exhibits a detectable
change in property in response to changes in concentration
of specific vapor components relative to a selected
standardO It is preferred that the indicating component
of sensing element 16 be capable of exhibiting-a visible
change such as a change in color or optical propertiesO
Alternatively, the indicating component can exhibit non-
visible changes which can be detected such as a change in
conductivity, permeability, density, crystalline formg
and the likeO
- 1.5 -
` 106614~L
For devices used to monltor soll molsture9
chemicals~ such as hydrated salts, which visibly respond
to changes in relative humldity by changlng color, are
particularly suitableO A pre~erred hydrated salt is
cobalt chloride ~CoCl2 6H20)0 This salt, when applled
to or absorbed in a cellulosic material, gelatin, s~llca
gel, or polymeric materlal, can change from a pink to a
blue color depending on the level of the relatlve
humidity to which the salt is exposedO These salts
are well known and have been used in various humidity
indicating means as descrlbed in UOS. Patents 2,4~0,071,
2,580,737, 3,702,755 and 3,788,1280
Salt mixtures comprising cobalt chloride with
other materials can also be used as indlcating components
15 of senslng element 160 Mixtures of cobalt chloride with
cobalt thiocyanate (eOgo equal parts by weight) have been
- used to provide a visible color change in the relative
humidity range of about 50 to 75 percent R~Ho U SO Pa~ents
2,460,074 and 3,788,128 describe the use Or these salt
mixtures as humidity indicating materialsO This combina-
tion of chemicals can be used to provide a pink color at
relative humidities above about 75% When the relative
humidity goes below 75% the indicating material gradually
changes to a lavendar color, becoming blue at a relative
humidity of about 50% ~nd belowO The humidity at whi~h
~he color change occurs can be ad~usted by varying the
ratio of cobalt chloride to cobalt thiocyanateO For
example, a sensing element can be prepared by sat~lrating
a piece of porous filter paper~ such as Whatman NoO 1
rilter paper, with a 20% aqueous composition of equal
- 16 -
¢
~06614~
parts by weight cobalt chloride and cobalt thiocyanate
and drylng the saturated filter paperO The response range
of the senslng element can be varled to some degree by
controlling the concentration of salt in the sensing
element,
A use~ul indicating component which exhiblts a
detectable color change over a relatlvely narrow relative
humidity range comprises a mixture of cobalt chloride with
a copolymer of polyvinyl pyrrolldone/vinyl acetate ("I 535,"
General Analine and Fllm). Copolymer to cobalt chloride
ratios of about 6:1 to about 1:1 are preferredO m e mixture
is dissolved in water and absorbed in or applied to an
absorbent pad or other carrier, and when dried provldes a
sensing element which exhiblts a readily observable color
change in the 70% to 80~ relative humidlty rangeO
In one embodiment o~ the device 10 shown in
FIGURE 1 the sensing element 16 is prepared by applying an
lndicating component directly to the underside of cover 140
For example, the cobalt chloride/copolymer solution
described-above can be coated on the underside of cover 1
in the form of a dot or other shape havlng a diameter of
about 0.5 to lo 5 centimetersO After the solution dries~
the coating which forms sensing element 16 ls ready for useO
In yet another embodiment-sensing element 16
can include as the indicating component a deliquescent
compound which exhibits a reversible change in optical
properties at a glven level of relative humidity~ Fo~
example, the sensing element 16 can comprise a coherent,
continuous layer of deliquescent compound which is 3paque
at humidlty levels below the point at which the compound
1066~4~
deliquesces and which becomes optically transparent on
dellquescing~ together with a layer underlying the
deliquescent compound which i5 at least partlally colored
ln contrast to the opaque compound so as to be observable,
and preferably conspicuous, when the compound deliquesces
and becomes transparentO
When the surrounding humldity is below a glven
level, the deliquescent compound remains opaque and the
underlying layer is not visibleO When the humidity rises
above the point at whlch the compound dellquesces, the
compound becomes transparent and the underlayer is visible
preferably conspicuous, to the observer, thereby indicat-
ing exposure to a selected level of relative humidity
within the envelope~ When the humidity level within the
envelope is again lowered below the deliquescent point of
the compound, the compound effloresces and again becomes
opaque and the underlayer is no longer visible to the
observerO In one embodiment the underlayer can be a
contrasting color or can have intelligence printed on
the surface thereof so that when the deliquescent compound
becomes transparent a conspicuous color or an appropriate
message such as "wet" or the like is observedO
A preferred means of providing a continuous
layer o~ deliquescent compound is to absorb a solution of
the deliquescent compound in a thin layer of tissue paper
and dry the paperO Sodium bromide is a preferred
deliquescent salt, although other deliquescent compounds
known in the art are suitableO The sensing element 15
~hich includes sodium bromide as the deliquescent compound
proYldes a change in optical properties when the relati~e
- 18 -
~066~
hum~dity within the envelope is about 57%O
When the device 10 is used to monitor the
concentration of vapor components other than moisture,
eOgO ammonia, the sensing element 16 comprises indicating
components capable of responding to changes in the
concentration of these specific volatile componentsO
For example, a device for monitoring the ammonia concen-
tration of soil can be provided by employing alizarin or
pH papers sensitive to the 3 - 5O5 pH range such as are
available commercially under the trade name "pHydrion"
papers from Micro Essential LaboratoryO Indicators
employing the "pHydrion" papers visibly respond by
changing color from yellow/orange to blue/green, which
color change is correlative to the ammonia concentration
(in parts per million) in the soilO
In addition, by selecting a sensing which
responds to other specific vapors, the monitoring device
may be used to detect and monitor the concentration and
change in concentratlon of various vapors such as the
oxides o~ nitrogen, sulfur and carbon, and the halogens~
FIGURE 2 is an alternate embodiment of a vapor
monitoring device according to the present inventionO
Monitoring device 20 is similar to that shown in FIGURE 1
comprising vapor permeable base 22, sensing element 2~,
25 and vapor permeable cover 260 Device 20 also contains a
protective layer 28 underlylng base 22 and containlng
pores 30O Layer 28 and cover 26 are shown extending
beyond base 22 and are ~oined at their periphery to
enclo~e base ~2 and sensing element 24 in a closely ccn-
forming envelopeO Protective layer 28 is shown as a
-- 19 --
~066~4~
porous layer which is permeable to vapor and whlch may be
permeable to llquid water since base 22 and cover 26 are
impermeable to liquids and protect sensing element 240
Protective layer 28 serves to protect base 22 during
handling and helps prevent base 22~ particularly when
base 22 is a porous mat of blown microfibers, from
becoming clogged with dirt and the li~eO Representative
of materials which can be used for protective layer 28 are
porous polyethylene films such as 3M Brand "TRANSPORE"
tape and a microporous tape having a non-woven backing
such as 3M Brand t'MICROPORE" tape, both available
commercially from the 3M Company.
FIGURE 3 is a cross section along line 3-3 of
the monitorlng device shown in FIGURE 20 As can be seen,
cover 26 together with base 22 and protective layer 28
envelop and closely conform to sensing element 24,
minimizing the free space within the envelope surrounding
sensing element 240
In order to operate successfully as a monitoring
device 10, 20, the sensing element 16, 24 shown in FIGURES
1-3 must be responsively coupled to the vapor source phase
at the interface so that the monitoring device can
accurately sample and compare a representative surface
vapor concentrationO This is achieved in the present
invention by enclosing the sensing element 16, 24 in a
sampling envelope defined by base 12 and cover 14 as in
FIGURE 1, or by base 22 and cover 26 as in FIGURE 20 The
sampling envelope shown in FIGURE 3 is adapted to rest on9
and intimately ~ontact 3 the surface of the vapor source
phase, such as the soil surrounding a potted plant, collect
- 20 -
106614~.
a representative sample of Yapors released from the
surface of the phase, and present the sample to sensing
element 16, 240
Due to the difference in vapor transmisslon
rates between the cover 14, 26 and the base 12, 22 a
sudden change in vapor input through base 12, 22 will not
cause the interior of the envelope to become immediately
overwhelmed with or starved of vapor; that is, the vapor
concentration within the envelope may be slightly
different than the actual vapor concentration at the
base-vapor source phase interface until steady state is
achieved This lagging response tends to reduce any
effect of transient peaks and valleys of vapor concentra-
tion released from the vapor source phase~
Further, the relatively slow vapor transmission
rate of the cover 14 prevents the vapors entering the
envelope through the base 12, 22 from being overwhelmed
by vapors entering through the cover 14, 26 from the
surrounding atmosphereO Temporary changes ln relative
humidity in the surrounding envlronment will have little
or no effect on a sensing element sensitive to changes in
relative humidityO However, constant operation at
humidity levels above the selected standard relative
humidity, eOgO above 75% R~Ha~ which has been found to be
a useful R~Ho Standard, may ultimately overcome the
monitoring device and impair the ability of the device
to accurately indicate the selected parametric moisture
concentrationO
Although cover 14, 26 is relatively less
30 permeable than base 12, 22 3 the cover must have the
~066~41
aforementloned minimum vapor transmission rateO If cover
14, 26 does not have the necessary vapor transmiss~on rate3
moisture or other vapors can accumulate within the
envelope and allow undesirable condensation in the envelopea
causlng the sensing element 16, 24 to be contacted by bulk
liquid which can leach chemicals from the sensing element
or cause a false reading by a humidity sensitive sensing
elementO
The monitoring device of the pre~ent invention
should be large enough to sample vapor released from a
representative area of the vapor source phaseO Discs
about lo 25 to 5 cm in diameter have been found sufficient
to provide accurate resultsO Shapes other than discs can
be used with equivalent resultsO
A disc of about 205 cm in diameter is an effec-
tive compromise size to achieve convenlent handling and
accurate samplingO This allows the device to accumulate
vapors released from about 5 cm of the surface of the
vapor source phaseO
Because the vapors reside in the monitoring
device for a short period of tlme before passing through
the cover, some mixing of the vapors takes place and the
monitoring device, in effect, averages the concentration
of vapor with time and over the area covered by the device
and can provide a more accurate reading than a wick or
other point sampling device can provideO
Generally monitoring devices having a base area
of less than about 1025 cm2 are not preferred since the
device becomes difficult to observe and handle and does
not s~mple a l.arge enough area of the vapor source phase
- 22 -
1~6~4~
surfaceO Monltoring de~ices which have a base area of
greater than about 20 cm2 can function effectively but
may be too large for some applications, for example, they
may be difficult to fit into small quarters such as a
small flower pot or may be unsightly in a small flower potO
When used for monitoring the available moisture
content of soil around potted plants, the monitoring device
is located on the surface of the soil in close proximlty
to the potted plant as shown in FIGURE 40 When the plant
is watered and the soil has sufficient moisture, the
sensing element which is visible through the cover has a
detectable characteristic property such as a characterlstic
colorO As the moisture is taken from the soil by the plant
and by evaporation and reaches a parametric concentration,
eOgO the moisture concentration determined to be ~ust above
that at which the plant will wilt, the relative humidlty
within the device will fall to a level below the selected
standard, e.gO 75% R~Ho ~ and the sensing element changes a
detectable property, eOgO colorO This change indicates
the need for additional water in the soilO The addition
of water to the soil so that the moisture concentratlon
in the soil rises above the parametric amount causes the
initlal detectable property, eOgO the initial color, of
the sensing element to return after a short equilibration
~5 periodO
Because the monitoring device protects the
sensing element from bulk liquid, plants can be watered
with the monitoring device in position next to the plant,
although it is preferred to ha~e the monltoring devLce
remo~ed dur.ing wateringO In tests using the monitoring
~6614~
device of the present lnvention to regulate the waterlng
schedule of a wide variety of plants in both heavy and
light soils, the plants thrived and did not suffer from
overwatering, as did plants which had their watering
schedules fixed by prior art, wick-type devicesO
The monitoring devices are useful to detect
and indicate the presence of moisture in other environ-
mentsO Particularly the monitoring devices have proven
useful in detecting the presence of certain levels of
liquids in body dresslngs such as dlapers and surglcal
dressings, thereby eliminating the need to touch or
remove the articles for examinatlonO This is particularly
useful where the body dressings have a liquid-impermeable
outer covering, eOgO polyethylene film, and the presence
of moisture is not detectable by touching the outer
surface of the dressingO A monitoring dev~ce, simllar
to that shown in FIGURES 1-3 or having other shapes, can
be attached to the dressing with the base resting on the
dressing and the cover disposed outwardly of the dressing
and the body to whlch it is applied~ When the body
dressing becomes moist, the monitoring device can
indicate, eagO change color, when the moist condition
existsO
Where the body dressing has a vapor permeable
covering, eOgO polyethylene, the monitorlng device can be
incorporated into the dresslng using a portion of the
outer covering of the dressing as the cover of the
monitoring device.
The monitoring devlces can also be uæed to
detect and lndicate vapQrs from decomposlng matter in
- 24 -
1o66l~l
solld and llquid phasesO For example, a monitorlng
device having a sensing element which is responsive to
ammonia can be placed on proteinaceous matter such as
fish, and the concentration of ammonia produced by
decompositlon detected and indlcatedO Alternatively,
the indicators can be floated on a pool of liquid such
as sewage or other effluent streams and detect and
indicate vapors dissolved therein or produced by
decompositlon within the liquidO
The following examples will serve to illus-
trate the practice of the method and the use of the
vapor monitoring devices of the present inventionO
Example 1
To demonstrate the utility of the monitoring
devlce in indicating the need for watering a potted plant
at proper intervals, a monitoring device was prepared as
in FIGURES 2 and 3 wherein protective layer 28 was a
205 cm diameter disc of a microporous polyethylene film
(3M brand "TRANSPORE" tape, 3M Company)g pad 22 was an
oil sorbent pad of blown polypropylene microfibers,
sensing element 24 comprised a mixture of equal parts
hydrated cobalt chloride and cobalt thiocyanate absorbed
in a disc of NoO 1 Whatman filter paperO CoYer 26 was a
piece of cellulose acetate film (3M brand "Magic Mendlng"
tape, NoO 810, 3M Company) adhesively bonded to protectlve
layer 280
Several zebra plants (Aphelandra) were potted
in 15 cm diameter foamed plastic azalea pots 13 sm deepO
A light potting soil of equal parts peat and vermiculite
(Terra-Lite "Redi-Earth'l~ WO Ro Grace CoO~ was used for
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~06614~
some plants, while a heavler clay loam was used fsr
othersO Zebra plants were used because they are partic-
ularly sensltive to moisture and prone to wilting lf
given insufflcient waterO
The plants were kept indoors at room temperature
(22 C) at a fairly constant relative humidity of about
20% RoH~ with fluorescent lightlngO
The plants were properly watered so the surface
of the soil was moist and the monitoring devices were
placed next to some of the plants on the leveled soil
surfaceO The plants were watered during the remainder
of the testO
The color of the monitoring devices changed from
the original pink color to a visibly detectable lavender
color after about 11 days for the plants in the light 50il
and after 7 days for the plants in the heavy soil (corres-
ponding to a humidity level within the monitoring device
of about 70-75% RoHo ) ~ The weight % moisture in the top
205 cm of soil and the bottom 10 cm of soil in each pot
was then separately determined~
Other plants were monitored by employing the
common method of touching the soil surfaceO When the
surface was dry to the touch (6 days heavy soil, 10 days
light soil) the weight % moisture in the top 205 cm and
bottom 10 cm of soil was determined~
Plants containing wick-type indicators were
also tested and the soil moisture measured as above when
the need for water was indic~ted (1 day heavy soil, 7 days
light soil)O
_ 26 -
~066141
In addition, some soil samples were allowed
to dry to the polnt where the plants wilted (12 days
heavy soil, 17 days light soil) and the moisture in the
top 205 cm of soil then determinedO
The results of the molsture tests were as
follows:
W~
Monitoring _ _ D~ S9~l_ ____
Devloe Uaed Top Bottom Top Bottom
- 205 cm 10 cm Time ~ 10 cm Time
lo Wick-Type21% 22%1 day 74% 75% 7 days
Device
2. Touch 12% 16%6 days 62% 67% 10 days
Monitor-9% 14%7 days 57% 65% 11 days
ing Device
of the
Present
Invention
4. Wilting6% -- 12 days 46% -- 17 days
The above data indicate that the monitoring
device of the present invention can be used to accura~ely
indicate a parametric concentration of moisture in soll,
io eO in this case the point at which the plant needs water
before wilting, and can closelg approximate the point at
whlch an experienced horticulturalist would indlcate the
need for waterO
The wick-type devices indicated the plant
required water before the moisture level was sufficiently
: low to require water,
Example 2
A False Aralla (Dizygotheca elegantissima) plant
about 1 meter high was potted in a pot 25 cm in diameter
- 27 -
106614~
and 20 cm deep contalnlng a sandy loam soil and exposed
to the conditlon of llght, temperature, and relative
humldity as in Example lo Touch tests indicate this plant
should be watered about every 9 days under these condl-
tlons in order to thrlve
A monltoring devlce was prepared as in Example 1
and placed on-level soil in the pot near the plant~ The
initlal pink color changed to lavender in a perlod of
between 9 and 10 daysO Upon watering the soil to satura-
tlon the color changed back to plnk after about 15 - 30
mlnutes and remalned plnk for another perlod of 9 - 10
days, and then agaln changed to lavender, and the waterlng
repeated.
After 3 months of this repeated watering cycle,
the plant was thriving.
E~
Monitoring devices were prepared as in Example 1
except that the sensing elements comprised 3 - 5O5 pH
"pHydrion" papers (Micro Essential Laboratory)O
Soils having various ammonla content were placed
in polyethylene bags, the monitoring devices placed on the
leveled surface of the soil within the bags, and the bags
sealedO After 90 minutes the indicators were observed on
each soil sampleO The ammonia content of the soils were
confirmed by analysisO The results were as follows:
- 28 -
1~6619L1
Soil Soll Ammonla
Sample NoO Indicator Color Con~ent, ppm
1 Dark green/blue 7,8
2 Green 4O8
3 Faint green/yellow lo 8
4 Yellow/orange Not detected
The monitoring devices were successful ln
differentiating between soil samples having differing
ammonia contentO
E ~
A disposable diaper having a polyethylene llquid
impermeable covering was modified by cutting a hole in the
outer covering and attaching a monitoring device similar
to that described in Example 1 over the hole wlth the base
of the device adjacent the diaper fabricO The diaper was
then applied to a baby in the conventional mannerO When
the diaper became wet with urine, the sensing element
changed from blue to pink indicating the need for changlng
the diaper,
ExamPle 5
A monitoring devlce like that described in
Example 3 was used to indicate the state of decomposition
' of crabmeatO Three samples of crabmeat were obtainedO
The first sample was fresh; the second evidenced some
decomposition but was still edible, while the third was
decomposed to a polnt where the meat was not edible,
Twenty to fifty gram samples were placed in glass beakers~
the base of the monitoring devices placed on the crabmeat
samples, and the beakers coveredO
- 29 -
~66~4~
After one hour the monitoring device on the
flrst sample showed no color change, while the devlce on
the second sample had turned slightly green at the edges
of the sensing element, After 10 minutes the senslng
element of the device on the third sample had turned
completely green. Thus, the monitoring device can be
used to accurately detect and indicate unwanted or
dangerous decomposition in food products by detectlng the
vapors issuing therefrom.
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