D – 99 Standard Test Method for Refractive Index and Refractive Dispersion of Hydrocarbon Liquids, hydrocarbons, refractive dispersion, refractive index. ASTM D(R07) – Designation: D – 02 (Reapproved ) An American National Standard. As well as adding a sample changer or special density cell for high pressures and temperatures, a DMA Generation M density meter from Anton Paar (Austria) .
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D — 02 Reapproved An American National Standard Standard Test Method for Refractive Index and Refractive Dispersion of Hydrocarbon Liquids1 This standard is issued under the xed designation D ; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon e indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense. NOTE 1—The test method may be suitable for measuring the refractive indices of liquids above 1.
Verication of the accuracy of such measurements will depend upon the availability of reliable, certied reference standards that demonstrate the performance of the instrument used under the particular measuring conditions.
For convenience in calculations, the value of the difference thus obtained is usually multiplied by 10 It may also be dened as the sine of the angle of incidence divided by the sine of the angle of refraction, as light passes from air into the substance. This is the relative index of refraction. If absolute refractive index that is, referred to vacuum is desired, this value should be multiplied by the factor 1.
The numerical value of refractive index of liquids varies inversely with both wavelength and temperature. Summary of Test Method 4.
Refractive Index Measurements According to ASTM D1218
Liquid color should be limited to No. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Current edition approved Nov. Originally approved in Last previous edition approved in as D — Originally published as Lawrey, D. The instrument principle is based on the critical angle concept. Signicance and Use 5. However, this instrument is no longer manufactured. There is a variety of refractometers that have been found to be suitable for this measurement.
Some instruments offer a wider measuring range but it is important to verify the uniformity of accuracy across the entire measuring range and to ensure suitable calibration materials are available for this verication. Reagents and Materials 7. Vapors may satm ash re. If an external bath is used, the thermostating liquid shall pass the temperature measuring device on leaving, not on entering the prism.
The temperature control v1218 external or internal shall have the following control specication: Stability Uniformity Display Resolution 6 0. Warning—2,2,4trimethylpentane, methylcylcohexane, and toluene are all ammable. Their vapor can be harmful. The precision of the test method see For apparatus using nonmercury in glass thermometer, a platinum resistance probe, thermocouple, or equivalent temperature sensors are acceptable. NOTE 3—Measurement of refractive dispersion requires more than one type of light source.
The sample shall be free of suspended solids, water, or other materials that may settle onto the prism surface and affect the measured reading. Water can be removed from hydrocarbons by treatment with calcium chloride followed by ltering d12118 centrifuging to remove the desiccant.
The possibility wstm changing the aatm of the sample x1218 action of the drying agent, by selective adsorption on the lter, or by fractional evaporation, shall be considered. Warning—Volatile hydrocarbon samples are ammable. Preparation of Apparatus 9. Dust and oil can impair the optical component of the instrument. Thoroughly clean the prism faces with toluene, 2 6.
Filters can be used to eliminate unwanted lines borderlines. Do not dry the prism faces by rubbing with dry cotton. Turn on the light source and allow the refractometer to equilibrate for 30 min. NOTE 6—The constancy of the prism temperature can be seriously d12218 by variations in ambient conditions such as air drafts or changes in room temperature.
Reasonable precautions should be taken to minimize these factors. Determine the refractive index at the secondary wavelength following Satm 7—When determining refractive dispersion, it is expected that the instrument would astk been calibrated at both wavelengths used. Open the prism assembly.
Apply a drop of 1-bromonaphthalene contact liquid, about 1. Press the reference standard against the surface of the prism face with the polished end towards the light source. If the observed refractive index for the chosen reference material astmm a specied test temperature differs by more than 0. Check that the prism temperature is within 0. Close the prism assembly and lock if necessary.
Turn on the light source. Allow 3 min temperature equilibration time. Calculation and Report Report the calculated value and the test temperature, for example: Precision and Bias The instrument shall incorporate a solventresistant prism seal. The accuracy and resolution awtm the temperature measuring device shall be 0. Reagents and Materials Preparation of Apparatus Ensure that the instrument has a solvent resistant prism seal.
They may require a atm, two-point, or multi-point calibration. Ensure the prism temperature is correct and the instrument has been properly calibrated. Do not introduce an excessive amount because this can slow the thermal equilibration. Lower the sample presser if tted. Record or report, or both, this value as the refractive index of the sample at the test temperature. NOTE 8—From experience using the instrument, the user will be able to judge with a safe margin aatm amount of time needed for a sample to thermally equilibrate on the prism.
Based on this, it may be possible on some models to set an automatic delay time for readings. This enables a xed measuring time to be written in to the experimental protocol.
NOTE 9—When successive readings are drifting, the direction of drift will indicate what is happening to the sample. An upward drift means the sample is cooling on the d218 a downward drift means the sample is warming up. This is particularly noticeable when samples are much hotter or cooler than the prism.
This can be manually recorded or, if the refractometer is equipped with a computer interface, readings can be sent to a printer or to a computer. D — 02 Rautomatic 5 0. The relative change in refractive index with temperature temperature coefficient is different for each liquid under test. Hydrocarbon liquids have a higher temperature coefficient than water and aqueous solutions.
For hydrocarbon liquids, the coefficient will typically be in the range -3 3 to -5 3 Refractive index should, therefore, be measured using light of a single wavelength monochromatic light. Most measurements traditionally have been made at the sodium D line Other light sources include mercury, cadmium, helium, and hydrogen where lters are used with the refractometer to eliminate unwanted emission lines.
Different substances have varying degrees of refractive dispersion sometimes called dispersive power. Some instruments can utilize a white light source, but often these instruments are limited in accuracy because of sstm light source. High accuracy Abbe refractometers require a pure spectral light source such as a sodium arc lamp see 6.
The refractive index at this wavelength is denoted as nD.
The degree of impurity band width will cause a dispersion of the detected light from the sample. Instrument software can be used to compensate for and thus minimize this error source but it will nevertheless be a factor in determining the limiting accuracy of the instrument. The dispersion error will however differ according to the substance measured. This is why instrument manufacturers may specify the instrument accuracy as typically or better than in order to cover a broad application scope.
However, for practical purposes, because of the proximity of the lines, it is regarded as a single wavelength source and the average value of The optical system in a refractometer is subject to microscopic movement as materials expand and contract with uctuating ambient thermal conditions. This effect leads to calibration drift, which must be periodically corrected to ensure measurement reliability. Solid plates are often preferred for their stability shelf lifebut have the disadvantage of limited accuracy in use because of the errors associated with the placing of the plate on the refractometer prism.
Typically, a plate may not allow an accuracy better than Test plates are particularly difficult to apply to sapphire prisms of the type typically used in digital electronic refractometers. This is because the micro-roughness of sapphire is greater than that of softer optically atter glasses used in optical Abbe refractometers.
Invariably, liquid reference standards will be preferred and will be recommended by instrument manufacturers for this reason. Automatic digital refractometers may require a single zerotwo-point, or multi-point calibration.