Abstract: A plurality of magnets is provided in an illumination prism carrier of a transmitted light refractometer and a corresponding plurality of magnets is provided in a sample prism housing of the refractometer to align a light exit surface of the illumination prism relative to a sample surface of the sample prism and urge the optical surfaces together in an even and uniform manner. The magnets replace mechanical biasing arrangements for positioning the optical surfaces and function to consistently reproduce a measurement optical path in the instrument for improved accuracy and repeatability of measurements.

Abstract: A hand-held automatic refractometer comprises a linear scanned array having a plurality of photoelectric cells and an optical system for directing light onto the array, the particular photoelectric cells of the array which are illuminated by said light being determined by the index of refraction of a sample substance placed on a sample surface of a prism of the optical system. A reflective surface is arranged close to the array at an acute angle thereto for directing primary light from the sample-prism boundary to the array, and for redirecting stray reflected light from the array back onto the array. The disclosed refractometer has a compact design wherein the linear array extends in a direction substantially parallel to the prism sample surface. The prism is mounted in a housing and the sample surface faces upward to allow access through a sample well of the housing, while the array is mounted in the housing facing in a downward direction.

Abstract: A sensor apparatus and associated method for sensing and monitoring specific binding of analyte to an immobilized binding layer are disclosed. The apparatus preferably comprises an automatic critical angle refractometer having a linear scanned array and an optical system for illuminating a portion of the array, which illumination depends upon the refractive index of the binding layer deposited on an optically transparent element. The apparatus further includes a flow cell for bringing the analyte in contact with the binding layer. The apparatus also includes a computer for receiving and processing refractive index data from the critical angle refractometer during the reaction between the analyte and the layer, which computer may be peripherally connected to the refractometer or enclosed within the refractometer housing.

Abstract: Disclosed herein is a sensor utilizing attenuated total reflection. The sensor includes a first dielectric block; a thin film layer, formed on a first face of the dielectric block, for placing a sample thereon; and a light source for emitting a light beam. The sensor further includes an optical incidence system for collimating the light beam, and making the collimated light beam enter the dielectric block at a predetermined incidence angle so that a condition for total internal reflection is satisfied at an interface between the dielectric block and the thin film layer; a photodetector for detecting the refractive index distribution of the sample obtained within a plane along the interface, by detecting an image carried by the light beam totally reflected at the interface; and an optical compensation system for compensating for image distortion produced by the dielectric block when the predetermined incidence angle of the light beam varies.

Abstract: The present invention relates to a method for the determination of refractive indices, ranging over a wide range of values. It also relates to a method for the determination of the birefringence of liquid crystals. Further, it relates to optical instruments used for such determinations.

Abstract: A refractometer which provides a “sugar” or “diet” indication when immersed on a beverage. The device is electronic and lights either a “sugar” or “diet” signal to the user. A prove has a light source and a photodetector at one end and an angled face at the other end. Depending on the refractive index of the beverage, the light is either reflected back into the probe and into the photodetector and exits out of the angled face and does not reflect back to the photodetector.

Abstract: A system for determining the condition of an optical signal includes a first refractive material having an interface with a second refractive material. The first refractive material receives an optical signal. A portion of the optical signal reflects off the interface between the first refractive material and the second refractive material as a reflection signal. A signal monitoring circuit determines the condition of the optical signal using the reflection of the optical signal at the interface between the first refractive material and the second refractive material.

Abstract: A method for monitoring the interaction of molecular species utilizes a sensor device comprising a substrate (1) with a waveguide (2) formed on the surface thereof. A grating (3) is formed in one of the surfaces of the waveguide (2). A beam of light (6) is incident on the grating (3) and the angle of incidence at which maximum reflection occurs is monitored. A first molecular species is immobilized on the waveguide (2). Changes in the angular position of the reflection maximum provide an indication of interaction of the first molecular species with a second molecular species contained in a sample brought into contact with the sensor device.

Abstract: An illuminator for use in a refractometer having a body housing, a sample cover assembly, a prism assembly and measuring assembly for measuring the composition and density of a substance. The illuminator includes a light source, a power source for operating the light source and an operating means for selectively activating the light source. The illuminator is located in the refractometer housing such that the light source is in a position on or about the prism assembly to illuminate a fluid substance to be measured. Light from the light source is introduced at a grazing incidence to a measuring surface of the prism. Phosphorescent material in the sample cover provides reticle illumination.

Abstract: A single fiber optic probe capable of measuring at least two different properties of a medium. More specifically, a single probe having an integral optical element which is capable of directing light to perform at least two distinct spectrometric analyses on a medium. For example, the single probe may be used to monitor a solid phase and dissolved solids in a multiphase medium.

Abstract: Disclosed is an integrated miniaturized biochemical sensor (50) which can be used to make critical angle measurements resulting from the differences in refractive index between the sensor's housing (55) and a given sample (40). In one embodiment, the sensor includes a device platform (111) over which an encapsulating and light transmissive housing (115) is formed to enclose the various sensor components including a light source (105), and a photodetector (107), a signal processing unit (95) and a temperature sensor (95). In another embodiment the housing (115) has a reflective mirrored surface (119) which focuses the light (117) from the light source (105) onto a sensing surface (121) which is in interact with the sample (40) of interest. Light incident from the sensing surface (121) is directed at the photodetector (107,159) which may be an array or single cell. A temperature sensor (95) may also be included and coupled to the platform (111).

Abstract: A novel method for measuring a deposit point is provided, which makes it possible to quickly and accurately measure a cloud point. A test sample is irradiated at an angle of incidence .theta. with an incoming light beam which satisfies an expression .theta.<.theta..sub.2 while gradually cooling the test sample such as gas oil, and a totally reflected light beam from the test sample is detected for every temperature, provided that .theta..sub.2 represents a critical angle of total reflection of a deposit such as a paraffin component deposited when the test sample is cooled. The deposit point of the test sample is determined from a change in intensity of the totally reflected light beam with respect to the change in temperature. The light intensity distributions, detected by a sensor array at respective temperatures, are statistically processed to more accurately determine the deposit point.

Abstract: A refractometer, comprising a light source arranged in a frame structure, an optical window to be positioned in a process solution, means for directing a beam of rays from the light source to an interface between the optical window and the process solution, part of the beam of rays being absorbed partly into the solution and part of it being reflected back from the solution entirely and creating an image, in which the location of a borderline between a light area and a dark area depends on the refractive index of the process solution, and an image detector, by means of which the image created in said manner is observed.

Abstract: A refractometric apparatus and method for monitoring the percentage of water in hydraulic fluids employ a temperature sensitive device allowing a user to obtain accurate and correct readings of various measured properties. In particular, the temperature sensitive member comprises a prism-wedge-mirror combination in conjunction with a bimetallic strip. The combination ensures the proper angular displacement of a light beam inside the refractometric apparatus and, therefore, the correct reading of a parameter to be measured.

Abstract: An optical cavity resonator device is provided for conducting sensitive murement of optical absorption by matter in any state with diffraction-limited spatial resolution through utilization of total internal reflection within a high-Q (high quality, low loss) optical cavity. Intracavity total reflection generates an evanescent wave that decays exponentially in space at a point external to the cavity, thereby providing a localized region where absorbing materials can be sensitively probed through alteration of the Q-factor of the otherwise isolated cavity. When a laser pulse is injected into the cavity and passes through the evanescent state, an amplitude loss resulting from absorption is incurred that reduces the lifetime of the pulse in the cavity. By monitoring the decay of the injected pulse, the absorption coefficient of manner within the evanescent wave region is accurately obtained from the decay time measurement.

Abstract: A refractometric apparatus and method for monitoring the percentage of water in hydraulic fluids employ a temperature sensitive device allowing a user to obtain accurate and correct readings of various measured properties on the reticle of the apparatus. In particular, the temperature sensitive member comprises a prism-wedge-mirror combination in conjunction with a bimetallic strip. The combination ensures the proper angular displacement of a light beam inside the refractometric apparatus and, therefore, the correct readings on the reticle.

Abstract: To discriminate optically between the various phases in a three-phase fluid, a light beam (F) of non-zero divergence is injected into a detector block (10) made of a material whose refractive index is greater than the refractive indices of all three phases of the fluid. The block (10) has a sensitive zone (18) and a total reflection zone (20) such that incident rays (Ri) parallel to the axis (12) of the block strike the sensitive zone (17) at an angle of incidence (.THETA.i) and are returned parallel to the axis (12) by the total reflection zone (20). The angle of incidence (.THETA.i) is such that a first phase gives rise to almost total reflection, a second phase gives rise to almost total transmission, and a third phase gives rise to partial transmission and partial reflection.

Abstract: An optical sensor for determining an index of refraction of a substance being monitored includes a light source (20). An optical element (24) having a coupling surface (30) and a measuring surface (26) is arranged such that light directed into the optical element (24) through the coupling surface (30) is partially reflected twice from the measuring surface such that it is directed to and exits through the coupling surface (30). The measuring surface (26) is preferably spherical. An input optical fiber (22) having first and second ends directs light emitted from the light source to the coupling surface of the optical element. The first and second ends of the input optical fiber (22) are optically coupled to the coupling surface (30) of the optical element (24) and the light source, respectively. An output optical fiber (28) has first and second ends and directs light expelled from the coupling surface (30) of the optical element (24) to a photodetector (50).

Abstract: The proposed fibre-optic sensor is based on surface plasmon resonance and consists of a monomode fibre with multiple angled facets at its end face and suitable coatings. A first partial face is preferably metal-coated, a second is provided with a conventional detection layer, and the angle between the two partial surface is 30.degree., 45.degree. or 90.degree..

Abstract: A refractometer, comprising a frame structure, in which are arranged a light source, an optical window and a light sensitive detector, whereby the optical window is arranged to be positioned into contact with a solution to be measured and a beam of rays from the light source is arranged to be directed to an interface between the optical window and the solution, whereby part of the ray beam reflects back from the solution and part of it is absorbed partially into the solution and an image is created, in which the location of a borderline between a light and a dark area depends on the critical angle of total reflection, this angle being a function of the concentration of the solution, and whereby an information of the location of the borderline is arranged to be transformed into an electrical form by the light sensitive detector.

Abstract: An optoelectronic sensor 1 for detecting foreign bodies, especially raindrops on a windshield, includes an outer housing part 2 and an inner housing part as well as a fastening device 4, which is glued to a pane 5. A fastening means, for instance comprising two slides 6, is provided, guided in the outer housing part 2, and can be made to engage the fastening device 4 for securing the sensor 1 to the pane 5. In the interior of the sensor 1, the inner housing part, which carries the optoelectronic elements of the sensor 1, is pressed toward the pane 5 with a spring force braced against the outer housing part 2, in order to accomplish the optical coupling with the pane.

Abstract: Disclosed is a device for qualitative and quantitative in-vitro or in-vivo analysis of a sample by means of ATC (Attenuated Total Reflectance) while utilizing at least one radiation source, an ATR element as well as a detector unit. The present invention is distinguished by the combination of the following features: the radiation source generating a primary beam aimed at the ATR element, the primary beam impinging on the ATR element at an angle of .alpha., which is larger than the critical angle of the total reflectance .alpha..sub.T at the interface between an optically dense medium and a less dense one; the to-be-analyzed sample whose layer near the surface interacts with the primary radiation can be disposed on at least one side of the ATR element, a detector unit corresponding to the incidence angle of said primary radiation in the ATR element detects the radiation emitted from the ATR element.

Abstract: An apparatus for detecting a target substance in a pixel array is provided. The apparatus has a light source to emit a light suitable for exciting the target substance in the array, a total internal reflection (TIR) member, and a light detector. The TIR member has a TIR surface on which the array is located. The light from the light source passes into the TIR member and is reflected by the TIR surface. The array is within an evanescent field region at the TIR surface. The light detector is adapted to detect light emitted from the array as a result of evanescent excitation of the target substance.

Abstract: A method for refractometer measuring, in which a beam of rays emitted from a light source is transmitted to the interface between the optical window of a refractometer and the liquid to be measured, whereby part of the beam of rays is reflected back from the liquid and part is absorbed into the liquid and an image is produced in which the position of the boundary between a light and dark area depends on the critical angle of total reflection, the critical angle being a function of concentration of liquid, and in which the boundary between the light and dark area of the image is determined by light detectors arranged in a line. For good resolution, to the measuring data obtained from the light detectors is applied a mathematical model corresponding with the information provided by the measuring data and the position of the boundary is determined by means of this model.

Abstract: A dual mode illumination system for optical inspection of products for surface defects and defects in holes in the product includes a first light source for providing illumination along an axis of one or more holes in the product to be inspected, the first light source being positioned on a first side of the product, a second light source providing illumination of the surface of the second side of the product to be inspected, a beam splitter for redirecting light from the second light source to a light sensor while passing light from the first light source to the light sensor. The second light source may be located adjacent to a second side of the product to be tested with the axis of illumination parallel to a major plane of the product. The light sensor may be a video camera connected to a data processing and display system.

Abstract: Ice in particular and also other substances such as water and glycol-containing anti-icing fluids can be detected and distinguished by means of differences in their optical index of refraction. A plurality of beams at different angles of incidence are multiplexed onto the reverse side of an optical surface which is embedded in a surface to be monitored or otherwise positioned in a sampling environment. The reflected beams at the different angles are measured and refractive indexes calulated form the measured reflected beams. If the calculated refractive indexes are the same at all angles, then the substance is positively identified. If the values do not agree, then there is partial coverage, and the substance may be identified by comparison with predetermined values. The system is applicable to aircraft, where in-flight and pre-flight monitoring of icing conditions and surface contamination is needed.

Abstract: A sensor system for the measurement of the optical conditions at a boundary surface between a first medium that is a solid body and a second medium whose refracting indices are different. The sensor system has an optical unit comprising at least one sending unit with at least one sending element, at least one receiving unit with at least one receiving element, and an optical path connecting the send unit(s) to the receiving unit(s). A light-conducting body with a base surface and two optically active end surfaces is arranged in the optical path, where the base surface of the light-conducting body is attached to the surface side of the first medium between the sending unit(s) and the boundary surface. The first end surface of the light-conducting body is directed towards the sending unit(s) and the second end surface of the light-conducting body is directed towards the receiving unit(s).

Abstract: A refractive index sensor of a total-reflection type comprises a waveguiding layer of a cladding/core/cladding waveguide structure formed on a substrate. The waveguiding layer has an input face connected to either a single optical fiber or a plurality of optical fibers for injecting a light(s) into the layer, a detection face which, obeying Snell's law, totally reflects/transmits the light beam or beams that have arrived there with an expansion angle from the optical fiber or fibers and which constitutes a surface with which a material whose refractive index is to be measured comes in contact, and an output face which outputs the light reflected from the detection face and is connected to an optical detector. The refractive index of the material of interest is detected from a bright-dark boundary of the presence of the corresponding total reflected light from the detection face. With no need of a bulk prism or lamp-type light source, the sensor is small in size and high in sensitivity.

Abstract: An arrangement for cleaning an optical window in an instrument such as a refractometer located in-line in a continuous or batch process, comprising a nozzle for spraying under high pressure a harmless cleaning medium onto the optical window. The nozzle is firmly fixed in a nozzle frame, the frame itself being firmly attached to the instrument in the vicinity of the optical window. The nozzle is recessed in the frame. The invention achieves cleaning of the optical window without mechanical parts or strong solvents, and does not require removal of the instrument from its in-line position.

Abstract: The presence of trace materials in a sample is detected using both macroscopic and microscopic properties. A detector includes a light source and an optical resonator. The light source may be located either inside the resonance cavity of the resonator or outside the cavity, in which case it may be a semi-conductor such as a semi-conductor laser or a superluminescent diode. The detector also includes at least one reflective member that has a total internal reflection (TIR) surface and may be a passive device or an active gain element. Light from the light source is preferably focussed onto a single point of reflection on the TIR surface. The test sample is positioned within the evanescent field region of the TIR surface. Optical changes arising within the evanescent field region, such as excitation of fluorescence in the sample, changes in its refractive index, and changes in the resonant frequency of the optical resonator, are then detected.

Abstract: In an apparatus for detecting a property of a liquid, light is emitted from a light emitting element towards an interface between a liquid to be measured and a prism in an interface channel. Reflected light from the interface is received by a light receiving device, and a refractive index of the liquid is obtained from the total reflection critical angle. A cleaning member capable of contacting the interface by the flow of the liquid is provided. The cleaning member may be a small body or a floating member, a tape/string member having one end fixed to a channel wall, or a wiper swingable by the flow of the liquid.

Abstract: A gas density sensor having a prism in contact with a fluid whose density is determined. A light source shines light into the prism. The light is reflected off prism surfaces in contact with the fluid. As the fluid density changes, the amount of light reflecting off these surfaces changes depending upon fluid density. A detector placed to receive light reflecting off the surfaces determines density from sensed light.

Abstract: The presence of trace materials in a sample is detected using both macroscopic and microscopic properties. A detector includes a light source and an optical resonator. The light source may be located either inside the resonance cavity of the resonator or outside the cavity, in which case it may be a semi-conductor such as a semi-conductor laser or a superluminescent diode. The detector also includes at least one reflective member that has a total internal reflection (TIR) surface and may be a passive device or an active gain element. Light from the light source is preferably focussed onto a single point of reflection on the TIR surface. The test sample is positioned within the evanescent field region of the TIR surface. Optical changes arising within the evanescent field region, such as excitation of fluorescence in the sample, changes in its refractive index and changes in the resonant frequency of the optical resonator, are then detected.

Abstract: According to the present invention, there is provided an optical sensor capable of detecting, identifying or measuring a property of a solid, liquid or gas which is in contact with its measuring surface. The preferred sensor comprises an optically transparent sensing element with at least one surface, an optical energy source, means for conducting optical energy from the source to the sensing element at a specific, precisely determined angle and a photodetector. The measuring surface of the sensing element forms an interface with the substance to be measured. Optical energy is partially reflected from the interface formed at the planar surface of the transparent element toward the photodetector. It has been discovered that the resulting signal from the photodetector is proportional to the refractive index of the medium covering the outer surface of the transparent element.

Abstract: A measuring instrument utilizing surface plasmon resonance is described. The instrument employs no moving mechanical part because it produces the resonance by changing the parameters either electrically or acoustically, and it detects the reflection by a stationary detector.

Abstract: A prism providing an optical window for a process refractometer. The prism is manufactured from a material that has predetermined optical properties and a refractory index higher than the refractory index of the process material to be measured. One face of the prism is arranged to provide an interface in contact with the process material to be measured. To optimise the selection of the material of the prism, an optically transparent material layer is provided onto the surface of the interface in contact with the process material, the refractory index of the material layer being higher than the refractory index of the material that the prism is manufactured from.

Abstract: A method for measuring a refractive index profile and distributed dispersion of a sample by measuring refractive indices at a plurality of wavelengths at measuring points on the sample and calculating a refractive index profile at a main wavelength of the sample from the measured refractive indices.

Abstract: This invention uses the evanescent wave detection of particles to distinguish bound from free in an analyte-binding assay. Illumination below the critical angle is employed, and a beveled window is used to eliminate bulk fluorescence from the emitted evanescent wave liquid. The sample is held in a non-rigid film cuvette.

Abstract: A critical angle refractive index detector for production liquid chromatography systems with flow rates as low as 100 ml/min to 25 l/min or higher as the system requires and pressures up to 4000 psi. The detector includes a flow cell with a sensing chamber volume selected to provide maximum detector sensitivity and minimum pressure drop at the maximum flow rate of the system for accurate discernment of critical refractive index peaks of each constituent in the sample. Explosion protected controls for zero and span settings are located to the exterior of a purged safe enclosure containing the system.

Abstract: The physical properties of thin films can be examined with the aid of polarized light with which the film to be examined is irradiated while the reflected or transmitted light is deflected in the direction of an imaging system, the polarized light having the effect of exciting waveguide modes in the film to be examined.

Abstract: A critical angle refractive index detector for production liquid chromatography systems with flow rates as low as 100 ml/min to 25 l/min or higher as the system requires and pressures up to 4000 psi. The detector includes a flow cell with a sensing chamber volume selected to provide maximum detector sensitivity and minimum pressure drop at the maximum flow rate of the system for accurate discernment of critical refractive index peaks of each constituent in the sample. Explosion protected controls for zero and span settings are located to the exterior of a purged safe enclosure containing the system.

Abstract: The optical sensor for the detection of specific substances and refractive index changes in gaseous, liquid, solid and porous samples is composed of integrated optical elements. It consists of a waveguiding film (1) equipped with a diffraction grating (4) and applied onto a substrate (2). For the selective detection of a specific substance contained in the sample (3) a selectively chemisorbing additional layer (5) covers the film (1) at least in the grating region. The sample (3) is applied at least in the grating region either directly onto the waveguiding film (1) or onto the selectively chemisorbing additional layer (5). Chemisorption of the substance, which is contained in the sample (3) and is to be detected, to the selectively chemisorbing additional layer (5) results in a further adlayer (6) coating the waveguiding film (1).

Abstract: A liquid mixing ratio detecting sensor has cylindrical holder which is immersed in sulfuric acid solution. The holder is filled with silicone oil. A glass plate is placed within the holder. A light emitting diode emits light beams which enter the glass plate through its vertical side, and totally reflect from a boundary between the glass plate and the sulfuric acid solution. The light beams coming out from the glass plate is reflected by a reflection plate to enter into the glass plate through its vertical side, and totally reflected from a reference boundary between the glass plate and the silicone oil when a refractive index of the sulfuric acid solution is greater than that of silicone oil. On the other hand, the light beams entered into the glass plate refracts at the reference boundary to fall on a photo diode when the refractive index of the sulfuric acid solution decreases to be smaller than that of silicone oil.

Abstract: A mixing ratio detecting device for composite liquid has a transparent column placed so that a bottom of the column is in contact with a mixing liquid, and a light emitting diode disposed so that light beams therefrom are incident on one side of the column to pass therethrough so as to impinge on an interface between the bottom of the column and the mixing liquid. The light beams impinged on the interface less than a critical angle are refracted, while the light beams impinged on the interface more than the critical angle totally reflected to escape from other side of the column. A photo diode is provided to receive the light beams escaped from the other side of the column so as to generate an output. An effective photo-receiving area of the photo diode is in the form of an inversed trapezoid to compensate for characteristics of the output from the photo diode.

Abstract: An optical liquid level sensor has an optically-transmissive body (28) provided with a frusto-conical tip end portion (32). When the tip end portion is exposed to air, the angle of incidence (.theta..sub.i) of light at each of three points of reflection (b,c,d) is less than the critical angle (.theta..sub.c) such that substantially all light transmitted through the body will be reflected internally. However, when the tip end portion is exposed to a liquid, light is refracted, and the intensity of the reflected light is reduced. The intensity of the reflected light is used to indicate whether the sensor is above or below the surface of the liquid.

Abstract: A detector device for mixing ratio for gasoline and alcohol include an optically permeable column, one end of which is coated with a light-reflective layer. The circumferential surface of the column is at least partly immersed in mixing liquid of gasoline and alcohol.The light beams enter the column to be incident on said circumferential surface of the column and reflect from the circumferential surface to be incident on said light reflective-layer to reflect therefrom. The reflected light beams impinge on a photo diode which outputs in accordance with the intensity of the light beams impinged.The diametrical and lengthwise dimension of the column being determined such as to provide incidence angles of the reflected light beams changing from a minimum angle corresponding to the critical angle when the mixing liquid ratio is at the lower limit of the predetermined range to a maximum angle corresponding to the critical angle when the mixing liquid ratio is at the upper limit of the predetermined range.

Abstract: A detector device for determining the mixing ratio of gasoline and alcohol includes a flint glass plate, one side of which is placed to be in direct contact with a mixing liquid of gasoline and alcohol, a light emitting diode is located at the other side of the flint glass plate to be opposite to the mixing liquid so that light beams emitted from the diode enter the flint glass plate to be incident on a boundary between the plate and the mixing liquid and a photo diode having a rectangular shape and located in coplanar relationship with the light emitting diode to receive the light beams totally reflected from the boundary.

Abstract: The invention relates to an optical device for measuring moisture in a substrate, in which device water is conveyed from the substrate along a porous absorption part (5) on a surface (4) of a prism so that is causes the critical angle of the total reflection to be changed thereon as a result of the change of the index of refraction. Another surface of the prism is dyed or patterned and covered in such a manner that it becomes visible only through reflection from the surface (4) when the surface is dry. When the surface (4) is moist, only the absorption part is visible through the viewing surface. The invention is advantageous in that due to the application of the principle of total reflection the change from an indication of the presence of moisture to an indication of the absence of moisture takes place sharply, not gradually.

Abstract: Processes are described in which solution composition is monitored by extremely accurate measurements of index of refraction involving measurement of reflectivity from a glass-solution interface. A particularly useful application is the swelling operation in metallizing polymer surfaces where dimethylformamate-water solution is contacted with the polymer surface to produce the swelling. Accurate, continuous control of the solution composition is necessary to insure optimum amount of swelling.

Abstract: A method and apparatus for continually measuring the specific gravity of a flow liquid. The liquid is caused to flow across a flat measurement surface defined by a light transmissive shelf member. The measurement surface, i.e. the interface between the shelf member and liquid sample thereon, is illuminated by rays incident at angles greater than and less than a critical angle to reflect a boundary line whose position is dependent on the critical angle and thus the specific gravity of the liquid sample. The reflected boundary line is projected onto a photovoltaic surface which, together with detector electronics, determines the position of the boundary line with respect to a boundary line position associated with a reference liquid. The difference in boundary line position is used by the detector electronics to determine the specific gravity of the sample by a table lookup procedure.