Note: Descriptions are shown in the official language in which they were submitted.
5~;~7G
This invention relates to a method and apparatus
for optical determination of the saturation temperature
of a solution.
A broad object of the present invention is to
provide a method and apparatus for optical determination
of the saturation temperature of a solution which obviate
or mitigate the disadvantages, as described below, associa-
ted with the prior art.
In one aspect, the present invention provides
a method for the optical determination of the saturation
temperature of a given substance in a solution subject
to test by a procedure involving the steps of placing the
solution in a test cell, suspending therein fine crystals
of the solute dissolved in the solution thereby preparing
a test specimen, mounting the test cell now containing
the test specimen on a mounting base formed in a tempera-
ture-adjustable heater, gradually elevating the tempera-
ture of the test specimen and throwing a light upwardly
at the test specimen, receiving the light penetrating
through the test specimen on a photoelectric element and
calculating the saturation temperature based on the tem-
perature of the test specimen and the amount of electricity -
generated in the photoelectric element, which method is
: characterized by causing the fine crystals of the solute
to be deposited fast in the form of a thin layer on the
light-penetrating surface of the test cell and then pour-
ing the solution on the deposited thin layer to prepare
a test specimen, mounting the test cell containing the
test specimen on the mounting base, gradually elevating
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the temperature of the test specimen and throwing light
upwardly at the test specimen, at that time an empty space
on the cell is made as a closed e~lpty space and pre-
heated air is passed through the closed empty space.
In a further aspect, the present invention pro-
vides an apparatus for optical determination of the satura-
tion temperature of a given substance dissolved in a solu-
tion under test which comprises a light source; a light
receiving unit above the light source, and having a light
receiving element and a first light path therein; a warmer
positioned between the light sou.rce and the light receiving
unit, the warmer having a secona light path therethrough;
a test cell supported by the warmer and extending through
the second light path; an air seal glass supported by the
warmer, the air seal glass being positioned above the test
cell and extending through the second light path such that
the distance between the test cell and the air seal glass
is between 0.5 mm and several mm; the warmer being capable
of warming the test cell; whereby light emitted from the
light source passes through the second light path, the
test cell, the air seal glass and the first light path,
and is received by the light receiving element so as to
optically determine the saturation temperature; the test
cell, warmer and air seal glass forming a substantially
closed space; air ducts pierced through the warmer and
communicated with the closed space; and means to introduce
a drying fluid to the closed space through the air ducts.
Embodiments of the invention, by way of example,
and of the prior art will now be described with reference
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to the accompanying drawings in which:
Fig. 1 is a sectional side view illustrating,
in general outline, an apparatus according to this inven-
tion;
Fig. 2 is a cross-section as viewed along the
line II-II of Fig. 1~
Fig. 3 is a partial sectional side view illus-
trating the steps for placing a test cell and an air seal
glass in the apparatus of Fig. l;
Fig. 4 is a sectional side view illustra-ting,
in general outline, a conventional prior art apparatus;
Fig. 5-a is a sectional side view of a typical
test cell;
Fig. 5-b is a sectional side view illustrating
the deposition of fine crystals on the lower surface of
the cell;
Fig.5-c is a sectional side view of a typical
test cell of improved design;
Fig. 5-d is an elevation of the test cell of
Fig. 5-c; and
Fig. 6 is a diagram of the characteristic curves
representing the relation between temperature and time;
and current and time.
; Recently, an improved saturation temperature
meter designed for optical determination of saturation
temperature has been reported in the International Sugar
Journal, Vol. LXXX, 1978, pp 40-43 (published at 23a
Easton Street, High Wycombe Bucks, England).
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As illustrated in Fig. 4, this temperature meter is
coMposed primarily of a light source 101, a heating unit 100 :
provided with a light path 104 and a mount 103 for a test cell
102, and a light-receiving unit 106 provided with a light-
receiving elernent 105.
The ter,lperature meter is prepared for operation by
placing a test solution in the test cell 102, adding and
suspending fine crystals of the solute in the solution to obtain
a test specimen, mounting the test cell 102 containing the test ~ -
specimen on the cell mount 103 and placing the heating unit 100
on top of the light-receiving unit 106. At this point, a space
108 is formed between a heat retaining glass 107 disposed in
the lower port.ion of the light-receiving unit 106 and the test
cell 102.
With the meter so preparedl light indicated by arrow
109 is admitted via the light path 1()4 upwardly towards the
lower end of the test cell 102; and a heater 110 is switched
on to effect gradual indirect heating of the test specimen in
` ; the test celL 102~ As the heating is continued, the temperature ~
20 of the test specimen increases and eventually reaches a point ~.
at which the fine crystals in the test specimen are dissolved. ~ ~:
:: :
: At this point, the light penetrating through the test cell 102 .
increases because the scattering of light is decreased on
dissolution of the fine crystals and, consequently, a relatively :
large change occurs in the amount of light being continuously
received by the light-receiving (photoelectric) element 105~ ~;
This change manifests itself in the amount of electric current
generated by photoelectric conversion in the photoelectric
element 105. The temperature of the test specimen is
continuously measured by a temperature measuring unit 111 which
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is held in contact with the lower surface of the -test cell 102.
This temperature meter, therefore, indicates the saturation
temperature of the solution under test with reference to the
aforementioned change in current generation and the corres-
ponding -temperature of the test specimen.
In a conventional saturation temperature meter such as
described above, during the elevation of the temperature of
the test specimen, the test specimen in the test cell 102 and
gas in the space 108 thermally expand. Consequently, an
increased portion of the gas and a small volume of steam
issuing from the surface of the test specimen leak into and
fill the space 108, giving rise to a state of stearn saturation.
In this case, the relation between the temperature of the test
cell 102 (Tl) and that of the heat retaining glass 107 (T2)
is Tl > T2 under normal working conditions. Consequently, part
of the steam filling the space 108 comes into contact with the
surface of the heat retaining glass 107 and forms dew-condensa-
tion thereon.
~: Experience shows that where the temperature (T2~ is in
: 20 the range of from 5 to 10 C, dew-condensation occurs when the
temperature diference (Tl - T2) is about 0.2C; and that
when the temperature (T2) falls within the range of from 25 to
30C, dew-condensation ensues when the temperature difference
(Tl-T2) is about 1 C.
When dew-condensation forms as described above, it
causes scattering of the liyht penetrating through the test cell
102 to impair the accuracy of determination. If the heating
rate is lowered enough to preclude dew-condensation, the rate
must be significantly reduced such that the determination
30 requires an excessively long time, the change in the intensity
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of the penetrating light occurs very slowly and the saturation
point determined is imprecise.
Further, with the conventional saturation temperature
meter9 the test specimen is prepared by suspending fine
crystals of the solute in the solution under test. Where the .
solution under test is very pure or where the solution is highly
supersaturated the initial crystallization (occurrence of
pseudocrystals) either during or after the preparation of the
test specimen proceeds very quickly so that the determination
demands a high degree of skill or the reproducibility of the
determined values is impaired.
With reference to Figs. 1, 2, 3 and 5-a, 1 denotes a
warmer which is generally constructed in a cylindrical form from
a metal such as cast aluminum which excels in thermal conduc-
tivity. Inside the warmer 1, a heat generator 2 i5 buried and
; used for elevating the temperature o:E the warmer 1 to a desired
level. The heat generator 2 can be, for example, an electric
heating coil capable of being adjusted to a desired temperature.
; The warmer 1, at the center thereof, contains a vertical
cylindrical opening to form a light path 3. The light path 3 is
so disposed that the light from a light source 4 positioned
under the light path 3 is collecte~ by a lens 5 and passed :.
upwardly through the light path 3. Inside the warmer 1, in the
upper part of the light path 3, a mounting base 6 is formed for
supporting an air seal glass 7 concentrically relative to the
light path 3. This mounting base 6, which serves as a mounting
base for the air seal glass 7, has a diameter greater than the
diameter of the light path 3. The mounting base 6 supports the
air seal glass 7 perpendicular to the light path 3. At a
prescribed distance below the moun-ting base 6 for the air seal
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glass 7, a mounting base 8 for supporting a test cell 9 is
concentrically formed rela-tive to -the mounting base 6. This
mounting base 8, which serves as a mounting base for the test
cell 9, maintains the test cell 9 parallel to the air seal glass
7. l'he distance between the mounting base 6 for the air seal
glass 7 and the mounting base 8 for the test cell 9 is so fixed
that, when the test cell 9 and the air seal glass 7 are set fast
in position on the respective mounting bases 6 and 8, a space 10
within the range of from 0.5 mm to several ~m is formed between
the cell 9 and the air seal glass 7. The space 10 is a
substantially closed space which is enclosed by the air seal
glass 7, the test cell 9 and the inner wall of the warmer 1.
Air ducts 11 fvrmed through the warmer 1 communicate with
respective ends of space 10, to permit flow of air through the
air ducts 11 and the s~ace 10 in the direction of the arrows.
The test cell 9 is, therefore, heated on both sides, i.e. on
its lower side by the heat received clirectly from the warmer 1
; and on its upper side by the heat from the circulating air which
has been heated by the warmer 1.
The test cell 9 is generally formed by inserting a
washer 13 made of a corrosion-proof, highly thermoconductive
metal such as, for example, brass between two clrcular glass
plates 12 and 12' disposed as illustrated in Fig. 5-a. The
lower glass plate 12' is joined fast to the washer 13, and the
upper glass plate 12 is separably mounted on the washer 13. Thus~
the test cell 9 contains a space for accommodating a test
specimen between the opposed glass plates 12 and 12'. A
temperature-measuring terminal 14 is disposed in a position
such that it will come into contact with the lower glass plate
12' when the test cell 9 is mounted in position on the mounting
base 8 for the test cell 9. Generally, a precision grade
thermocouple is used as the temperature-measuring -terminal 14.
Instead of using a construc-tion incorporating a washer as
described above, the test cell may be formed by simply combining
two transparent glass plates.
Denoted by 15 is a light-receiving unit, which is
removably mounted on top of the warmer 1. The light-receivi.ng
unit 15 is preferably composed of two different rnaterials; a
base 16 made of a heat-resistant synthetic resin of low thermal
conductivity and adapted to come into direct contact with the
warmer 1 and a member 17 disposed on the base 1~ and adapted to
support a photoelectric element 21. To ensure complete
dissipation of the heat transmi.tted from -the base 16, in order
to protect the photoelectric element 21 from possible temperature
elevation, the member 17 is preferably made of a material of
high thermal conductivity. Copper i'3 an ideal example of the
material for the member 17. By 16' are denoted legs projecting
from the lower side of the base 16. These legs 16l serve to
form a space between the warmer 1 and the base 1~ and, thereby,
form adiabatic insulation. Denoted by 18 is a light path,
leading to the light-receiving unit, which is formed coaxially
with the light path 3. A heat retaining glass 1~ is disposed
below the light path 18 for the light-receiving unit 15. Light
which passes through the heat retaining glass 19 projects
through a polarizing lens 20 onto the photoelectric element 21.
The photoelectric element 21 is formed of a photosensi.tive
matexial such as a photodiode. To support this element 21, a
rising portion 22 is formed at the central upper portion of the
member 17. Held in a fixed position at all times, the photo-
electric element 21 detects the amount of light received via the
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light-receiving path 18. The light which impinges upon this
photoelectric element 21 is converted into an electric current
An output terminal 23 is connected to the photoelectric element
21. This terminal is ex-tended and connected to a recorder or
measuring instrument which is not illustrated.
Now, the operation of the above-described apparatus
for the determination of satuxation temperature will be
described.
The apparatus is prepared for operation by, ~irst,
suspending in a solvent fine crystals of the solute dissolved
in a test solution; pouring the resulting suspension dropwise
onto the light-penetrating bottom face of the test cell 9;
subsequently vaporizing the solvent by suitable means such as
heating, thereby causing the fine crystals of the solute to be
firmly deposited in the forrn of a thin layer S on the light-
penetrating face as illustrated in Fig. 5-b.
The solvent used should be inert to the solute and
should vaporize at an appropriate rate. Where sucrose is used
as the solute, for example, acetone proves to be a suitable
solvent and brings about a satisfactorily fast deposition o~ the
solute. However, in this case, ether vapori~es too rapidly and
alcohol vapori~es too slowly to allow the desired fast
deposition of the solute. Of course, a mixture of solvents can
also be used.
Into the test cell 9, in which the fine crystals have
been firmly deposited in the form of a thin layer S as described
above, the test solution is slowly poured to cover the upper
glass plate 12, completing the preparation of a test specimen.
The test cell 9 containing the test specimen as
described above is set in position on the mounting base 8
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illustrated in Fig. 1. Above the test cell 9, the air seal
glass 7 is se-t in position on the mounting base 6. Preparation
of the apparatus for the determina-tion is then comp]eted by
moun~ing the light-receiving unit 15 on the warmer 1. Then,
air circulation through the air duct 11 is started and the
heat generator 2 and the light source 4 are switched on.
After 100 parts of light (representing a given
incident intensity) have entered the test specimen layer A
(Fig. 1), some part of the light is absorbed by the solution and
cell and some part thereof is randomly scattered by the fine
crystals forming the thin layer S. Consequently, less than 100
parts of the light penetrates through the cell ~ and reaches the
photoelectric element 21, there to be converted into a
corresonding amount of electric current.
Proportionally, as the temperature of the test specim~n
increases, the amount of light absorbed by the solution
increases, hence the light reaching the photoelectric element 21
decreases and the current generated decreases. The curve
plotting the current recorded continuously (as a function in mV)
with time indicates that the current decreases with the lapse
of time (Fig. 6).
As the heating continue~ to a point where the fine
crystals forming the thin layer S begin to dissolve, i.e. where
the saturation temperature is just passed, the scattering of -the
light begins to decrease owing to the decrease in the amount of
the fine crystals and the amount of light reaching the photo-
electric element 21 suddenly changes to an increasing trend.
Consequently, a point of inflection appears in the curve plotting
the continuous change of current generated. The temperature
which corresponds to this point of inElection is the saturation
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276
temperature of the solution under test. By com~ining the afore-
mentioned point of inflection and the temperature of -the test
specimen indicated on the temperature-measuring terminal 14,
therefore, the sa-turation temperature can be readily determined,
as shown in Fig. 6.
The test specimen to be used for the determination as
described above is prepared without entailing the step of causing
fine crystals of the solute to be suspended in the solution
under test as practised conventionally. Thus, the occurrence
of pseudocrystals during or after the preparation of the test
specimen is precluded and, consequently, the determination
affords accurate results.
Further, as described above, air which has been
warmed by the warmer 1 is blown into the space 10 formed by the
tes-t cell 9. The surface temperature of the air seal glass 7
defininy the upper boundary oE space 10, therefore, is substan-
tially equal to the temperature of the test cell 9. Therefore,
steam leaking from the cell 9 due to thermal expansion thereof
does no~ form dew-condensation in the space 10 as experienced
with conventional apparatus. Since the leaking steam is
constantly purged out of the space 10 by the current of air
flowing through the air duct 11, no steam stagnates anywhere
within the space 10.
The improvements noted above serve to expedite the
determination and, at the same time, greatly enhance the
reproducibility of the results obtained.
For the purpose of comparison, the method and apparatus
described herein and those of the conventional techni~ue were
used to determine the saturation temperature of a sucrose
solution. The resul-ts were as shown in Table 1. Comparison
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of the precision of determinal_ion,: expressed in terms of
standard deviation (S.D.) of the measured values, reveals that
the S.D. of the results obtained by -the method described
herein was relatively small and the average value agreed closely
with the theoretical value.
The procedure for tl~e determination and the results
of the determination (Table 1) are explained below:
This invention - the procedure followed for the preparation of
.
the apparatus (as shown in Fig. 1) comprised suspending in
acetone a small amount of suc:rose crystals pulverized in ad~ance
to a particle size of not more than 200 mesh; pouring the
resultant suspension dropwise and gradually onto the light-
penetrating bottom surface (glass plate 12') of the test cell 9
mounted on a hot plate heated to from 80 to 100C; allowing the
fine crystals to form an apparently uniform thin layer;
vaporizing the acetone thereby causing the thin layer of fine
crystals to be firmly deposited on the glass plate and, on
completion of the deposition of the fine crystals, allowing the
: test cell 9 to cool; gently pouring into the test cell 9 a
sucrose solution having a pur:ity of 99% and a total solids
content o~ 75% (w/w); and covering the test cell 9 with a
cover ~glass plate 12). Then, by following the procedure
described above, determining the saturation temperature by
heating the test specimen at rate of 5 C/minute.
Conventional techni~ue - a test specimen was prepared by gently
stirring about 5 y of a sucrose solution having the same
purity and concentration as mentioned above with 1 to 2~
W/V, based on the sucrose solution, of a more or less ~et
powder sucrose obtained by ce:ntrifuging sucrose crystals of a
particle size not exceeding 200 mesh in an alcohol, thereby
_ 12 -
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causlng the sucrose crystals to be suspended in the sucrose
solution. This test specimen was poured in~the test cell 9 and
the determination of saturation temperature was effected as
described above.
TABLE
. ~ Test ~
~ethod \ 1 2 3 4 5 Average S.D.
__ _ ~ _
rhis invention 63.1 63.9 64.2 63.4 63.6 63~64c + 0.38C
~onventional
technique 60.2 63.2 62.0 58.5 61.3 61~04C¦ + 1.6C
' ' ,:.
For the sucrose solution tested which had a concen- ;~
tration of 75~, the theoretical value of the saturation tempera
ture is 64C (as reported by Her~feld).
As a simple measure for effecting fast deposition of
a thin layer S of fine crystals of the solute on the light-
penetrating bottom surface of the test cell 9, the aforementioned
technique using the vaporization of the solvent may be
substltuted by a technique of fastening an adhesive tape to the -;
light-penetratlng bottom surface and allowing the fine crystals :~
of the solute to be laid firmly at a small thickness on the
tacky inner side of the adhesive tape; or by a technique of
applying a non-drying paste to the light-penetrating bottom
surface and similarly firmly depositing the fine crystals on the ~-
layer of paste, for example. ~:
Although the technique using the adhesive tape results
in slightly less precise results than the other two techniques
described above, the decrease in precision is not so large as to
pose any problem from the practical point of view.
; . : .
Z~76
The technique using the non-drying paste affords
results which compare favourably with those obtained by the
technique using -the vaporization of the solvent, when the
selection of the paste is appropriate.
In the comparative experiment described above, acetone
was used as the solvent. This does not mean that acetone is
the sole choice as the solvent. Depending on the nature of the
solute in use, other suitable solvents may be selected by
taking into account the heating temperature of the test cell 9
and the velocity of vaporization of the solvent.
Optionally, the device for circulating the preheated
air through the air duct 11 may be substituted by a device
which is adapted to preheat the air with a separate unit; a
device which directly feeds air preheated with an external,
adjustable heat source to the space 10 and discharges the
spent air from the space 10; or any other device which fulfills
the essential requirement that air with an adjusted ~emperature
should be delivered to and discharged ~rom the space 10 at a
fixed flow rate.
The ease with which the test cell 9 is inserted into
and removed frorn the apparatus may be enhanced by having a
smaller diameter for the upper glass 12 than for the lower glass
12' as illustrated in Fig. 5-c, and -d;and boring a small
pickup hole 24 at an exposed portion of the u~per surface of the
washer 13.
The following are examples of this invention.
The apparatus and method described above can, for
example, be used in the food and organic or inorganic chemical
industries to grow crystals in solutions. In particular, the
above described apparatus and method enable the determination
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of saturation temperature in l~ery pure or supersaturated
solutions which has been diff:icult with prior art apparatus
and methods.
EXA~LE 1
-
The test cell 9 was set on a hot plate at 90C. A
suspension prepared by suspending sucrose powder of a particle
size of 200-mesh-through in a concentration of about 1% W/V
in acetone was added dropwise to the test cell 9 and was
vaporized to form a very thin, uni~orm layer S deposited
~ir~ly in the test cell 9. AEter the test cell 9 was cooled,
a varying test specimen as indicated below was poured into the
test cell 9. The test cell 9 was mounted on the mounting base
8 in an apparatus constructed as shown in Fig. 1 to determine
the saturation temperature of the test specimen. The apparatus
was operated by feeding preheated air to the space 10 thereby
elevating the temperature o~ the test specimen at a rate of
3oc/minute -
The test specimen was prepared by allowing the
molasses produced at the Memuro Plant of Nippon Tensaiseito
~abushikl Kaisha to stand in a refrigerator at 5C for 60 days,
adding sucrose to the cooled molasses and keeping the resultant
mixture stirredinaconstant temperature bath (controlled
accurately to within 0.5C) for 72 hours thereby saturating
the mixture with an excess o~ crystalline sugar.
Test specimen A - Bath temperature 60 C, true sucrose
purity 56%
Test specimen B - Bath temperature 70 C, true sucrose
purity 60%
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'rest results (in C)
_
Test 1 2 _ 3 - 4 _ Averaqe _
rest Specimen A 61.2 60.5 60.3 61.6 60.3 60.8 + 0.53
rest Speci~,len B 69.8 69.0 69~0 69.3 70.1 69.4 + 0.41
_ _ _ . I
EXAMPLE 2
A double-faced adhesive tape made by 2~ichiban K.K. was
applied to accurately cover the inner bottom surface of the test
cell 9. Sucrose powder having a particle size of 200-mesh-
through was placed on the adhesive tape in the test cell 9 and
was blown with air to expel loose sucrose particles and leave
behind a very thin layer S of fine crystals firmly deposited in
the test cell 9. The same test specimens as used in Example 1
were poured in the test cell 9, and measured by following the
procedure of Example 1, with the temperature increasing rate
being fixed at 3C/minute.
Test results (in C)
_ .
Test 1 2 3 4 5 Average
_ _ ~ .
rest specimen A 61.8 61.0 60.959~8 62.6 61.2 + 1.1
_ _ .
~ rest specimen B 71.2 72.1 69.872.0 70.8 71.8 + 0.95
.. __ . _ -- .
EXAMPLE 3
.
A non-drying paste produced by Nogawa Chemical K.K.
and marketed under the trade mark designation of DIABOND 605 was
applied as a thin layer to the inner bottom surface o~ the test
cell 9. Sucrose ~owder having a particle size of 200 mesh-
through was placed on the non-drying paste in the test cell 9
and was blown with air to expel loose sucrose particles and
leave behind a very thin layer S of fine crystals ~irmly
deposited in the test cell 9. SpeCiMenS A and ~ were tested by
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following the procedure of Example 1, with the temperature
increasing rate being fixed at 3C/minute.
Test results (in C)
Test 1 2 3 4 5 Average ~ :
_ .
Test specimen A 60.259.4 61.160.5 60.7 60.4 ~ 0.57 .
Test specimen B 70.169.5 69.069.8 70.5 69.8 + 0.51
, ._
