ASTM D1218-12(2016)

Standard Test Method for Refractive Index and Refractive Dispersion of Hydrocarbon Liquids

SIGNIFICANCE AND USE
5.1 Refractive index and refractive dispersion are fundamental physical properties, which can be used in conjunction with other properties to characterize pure hydrocarbons and their mixtures.
SCOPE
1.1 This test method covers the measurement of refractive index, accurate to four decimal places or better, of transparent and light-colored hydrocarbons in the range of 1.3300 to 1.5000 at temperatures from 20 °C to 30 °C by manual (optical-mechanical) or automatic (digital) procedure.  
1.2 The manual (optical-mechanical) procedure also covers the measurement of refractive dispersion accurate to the fourth decimal place or better.
Note 1: The test method may be suitable for measuring the refractive indices of liquids above 1.5000 and at temperatures both below 20 °C and above 30 °C; however, the test method precision may not apply. Verification of the accuracy of such measurements will depend upon the availability of reliable, certified reference standards that demonstrate the performance of the instrument used under the particular measuring conditions.  
1.3 The test method may not be applicable to liquids that are strongly colored, or that have bubble points so near the test temperature that a reading cannot be obtained before substantial weathering takes place. Liquid color should be limited to No. 4 ASTM Color or lighter, as determined by Test Method D1500.  
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 WARNING—Mercury has been designated by many regulatory agencies as a hazardous material that can cause central nervous system, kidney and liver damage. Mercury, or its vapor, may be hazardous to health and corrosive to materials. Caution should be taken when handling mercury and mercury containing products. See the applicable product Material Safety Data Sheet (MSDS) for details and EPA’s website—http://www.epa.gov/mercury/faq.htm—for additional information. Users should be aware that selling mercury and/or mercury containing products into your state or country may be prohibited by law.  
1.6  This standard does not purport to address all of the safety concerns, if any, associated with its use. 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.

General Information

• Status: Historical
• Publication Date: 30-Sep-2016
• ICS: 75.080 - Petroleum products in general
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.04.0D - Physical and Chemical Methods

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D1218 − 12 (Reapproved 2016)
Standard Test Method for
Refractive Index and Refractive Dispersion of Hydrocarbon
Liquids
This standard is issued under the fixed designation D1218; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope and/or mercury containing products into your state or country
may be prohibited by law.
1.1 This test method covers the measurement of refractive
1.6 This standard does not purport to address all of the
index, accurate to four decimal places or better, of transparent
safety concerns, if any, associated with its use. It is the
and light-colored hydrocarbons in the range of 1.3300 to
responsibility of the user of this standard to establish appro-
1.5000 at temperatures from 20°C to 30°C by manual
priate safety and health practices and determine the applica-
(optical-mechanical) or automatic (digital) procedure.
bility of regulatory limitations prior to use.
1.2 The manual (optical-mechanical) procedure also covers
themeasurementofrefractivedispersionaccuratetothefourth
2. Referenced Documents
decimal place or better.
NOTE 1—The test method may be suitable for measuring the refractive 2.1 ASTM Standards:
indicesofliquidsabove1.5000andattemperaturesbothbelow20°Cand
D1193Specification for Reagent Water
above 30°C; however, the test method precision may not apply. Verifi-
D1500Test Method forASTM Color of Petroleum Products
cation of the accuracy of such measurements will depend upon the
(ASTM Color Scale)
availability of reliable, certified reference standards that demonstrate the
D6299Practice for Applying Statistical Quality Assurance
performance of the instrument used under the particular measuring
conditions. and Control Charting Techniques to Evaluate Analytical
Measurement System Performance
1.3 Thetestmethodmaynotbeapplicabletoliquidsthatare
D6300Practice for Determination of Precision and Bias
strongly colored, or that have bubble points so near the test
Data for Use in Test Methods for Petroleum Products and
temperature that a reading cannot be obtained before substan-
Lubricants
tial weathering takes place. Liquid color should be limited to
E1Specification for ASTM Liquid-in-Glass Thermometers
No. 4 ASTM Color or lighter, as determined by Test Method
D1500.
2.2 ASTM Adjuncts:
Determination of Precision and Bias Data for Use in Test
1.4 The values stated in SI units are to be regarded as
Methods for Petroleum Products and Lubricants, Version
standard. No other units of measurement are included in this
4.0.65
standard.
1.5 WARNING—Mercury has been designated by many
3. Terminology
regulatory agencies as a hazardous material that can cause
3.1 Definitions:
central nervous system, kidney and liver damage. Mercury, or
3.1.1 refractive dispersion, n—the difference between the
its vapor, may be hazardous to health and corrosive to
refractive indices of a substance for light of two different
materials.Cautionshouldbetakenwhenhandlingmercuryand
wavelengths, both indices being measured at the same tem-
mercury containing products. See the applicable product Ma-
perature.
terial Safety Data Sheet (MSDS) for details and EPA’s
3.1.1.1 Discussion—For convenience in calculations, the
website—http://www.epa.gov/mercury/faq.htm—for addi-
value of the difference thus obtained is usually multiplied by
tional information. Users should be aware that selling mercury
10000.
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Subcommittee D02.04.0D on Physical and Chemical Methods. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Current edition approved Oct. 1, 2016. Published November 2016. Originally Standards volume information, refer to the standard’s Document Summary page on
approved in 1952. Last previous edition approved in 2012 as D1218–12. DOI: the ASTM website.
10.1520/D1218-12R16. Out of print. No longer available from ASTM International Headquarters.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1218 − 12 (2016)
3.1.2 refractive index, n—the ratio of the velocity of light 6.4 Light Sources—The following type of light source can
(of specified wavelength) in air, to its velocity in the substance beusedinconjunctionwithanoptical-mechanical(Abbetype)
under examination. refractometer:
3.1.2.1 Discussion—Itmayalsobedefinedasthesineofthe
6.4.1 Sodium Arc Lamp, Na line at 589nm.
D
angle of incidence divided by the sine of the angle of
6.4.2 Mercury Arc Lamp, Hg line at 546nm or Hg line at
c g
refraction, as light passes from air into the substance. This is
436nm.
the relative index of refraction. If absolute refractive index
6.4.3 Cadmium Arc Lamp, Cd line at 644nm.
C’
(that is, referred to vacuum) is desired, this value should be
6.4.4 Mercury-Cadmium Arc Lamp.
multiplied by the factor 1.00027, the absolute refractive index
6.4.5 Helium Discharge Lamp.
ofair.Thenumericalvalueofrefractiveindexofliquidsvaries
inversely with both wavelength and temperature.
NOTE 3—Measurement of refractive dispersion requires more than one
type of light source.
4. Summary of Test Method
6.5 Light Filters—Arc lamps can emit a number of spectral
4.1 Therefractiveindexismeasuredusingahigh-resolution
lines that result in multiple-borderlines observed in the refrac-
refractometer of an optical-mechanical or automatic digital
tometer. Filters can be used to eliminate unwanted lines
type with the prism temperature accurately controlled. The
(borderlines). Depending upon instrument design, the manu-
instrument principle is based on the critical angle concept.
facturer will recommend and supply a suitable filter or adapt a
commercially-available filter (for example, interference filter)
5. Significance and Use
to suit the application.
5.1 Refractive index and refractive dispersion are funda-
7. Reagents and Materials
mental physical properties, which can be used in conjunction
with other properties to characterize pure hydrocarbons and
7.1 n-Pentane, 95 mol % Minimum Purity, for cleaning the
their mixtures.
prism faces. (Warning—Flammable. Harmful if inhaled. Va-
pors may cause flash fire.)
NOTE 4—Low boiling hydrocarbon fractions with boiling range 50°C
PROCEDURE A—MANUAL (OPTICAL-
to 100°C have also been found to be acceptable.
MECHANICAL) PROCEDURE
7.2 Toluene, HPLC Grade, for cleaning the prism faces.
6. Apparatus
(Warning—Flammable. Vapor harmful.)
6.1 Refractometer, high-resolution optical-mechanical re-
7.3 1-Bromonaphthalene, 98 mol % Minimum Purity, con-
fractometer of the “Abbe” type with suitable measuring range
tact liquid when calibrating with solid reference standard.
(1.3300 to 1.5000 or higher) and an accuracy/resolution of
(Warning—Toxic when ingested.)
0.0001 or better refractive index.
7.4 Primary Reference Materials, for calibrating the instru-
NOTE 2—Prior to 2001, Test Method D1218 was based on a Bausch &
ment.
LombRefractometer.However,thisinstrumentisnolongermanufactured.
7.4.1 Solid Reference Standard, with the value of refractive
Currentlyavailablemanualrefractometersareofthe“Abbe”type(critical
anglerefractometers,seeX1.2.3).Thereisavarietyofrefractometersthat index engraved on its upper face.
have been found to be suitable for this measurement. Some instruments
7.4.2 Distilled or Deionized Water,conformingtoTypeIIor
offer a wider measuring range but it is important to verify the uniformity
III of Specification D1193. At 20°C, n =1.3330; at 25°C,
D
of accuracy across the entire measuring range and to ensure suitable
n =1.3325; and at 30°C, n =1.3319
calibration materials are available for this verification. D D
7.4.3 2,2,4-trimethylpentane, 99 mol % Minimum Purity, at
6.2 Temperature Control Unit, either an external liquid bath
20°C, n =1.3915; at 25°C, n =1.3890.
D D
with both heating and cooling capability and pump for main-
7.4.4 Methylcyclohexane, 99 mol % Minimum Purity, at
taining the indicated prism temperature within 0.1°C, or an
20°C, n =1.4231; at 25°C, n =1.4206.
internal electronic temperature control system (such as Peltier D D
system). If an external bath is used, the thermostating liquid 7.4.5 Toluene, 99 mol % Minimum Purity, at 20 °C,
shallpassthetemperaturemeasuringdeviceonleaving,noton n = 1.4969; at 25 °C, n = 1.4941. (Warning—2,2,4-
D D
entering the prism. The temperature control unit (external or trimethylpentane,methylcylcohexane,andtolueneareallflam-
internal) shall have the following control specification: mable. Their vapor can be harmful.)
NOTE 5—Other pure materials may be used to calibrate the instrument
Stability ±0.1 °C
asprimaryreferencematerial,aslongastheycanbeobtainedin99mol%
Uniformity ±0.1 °C
Display Resolution 0.1 °C or better
minimum purity and accurate values of their refractive indices at specific
temperatures are available.The precision of the test method (see 15.1 and
6.3 Temperature Measuring Device, for those apparatus
24.1) were obtained using distilled water as the calibrant.
employingmercuryinglassthermometer,ASTMThermometer
7.5 Secondary Reference Materials, for calibrating the
17Chavingarangefrom19°Cto27°C,andconformingtothe
instrument.
requirements of Specification E1. For apparatus using non-
mercury in glass thermometer, a platinum resistance probe, 7.5.1 Mineral Oil Calibration Standards, measured and
thermocouple, or equivalent temperature sensors are accept- certified by suppliers for specific refractive index ranges and
able. temperatures.
D1218 − 12 (2016)
8. Sampling 11.2 For optimum accuracy, use a reference material whose
refractive index is close to the desired refractive index range
8.1 Asampleofatleast0.5mLisrequired.Thesampleshall
and temperature to calibrate the instrument.
be free of suspended solids, water, or other materials that may
settle onto the prism surface and affect the measured reading.
12. Procedure
Water can be removed from hydrocarbons by treatment with
12.1 Ensure that the prism faces are clean and dry. Check
calcium chloride followed by filtering or centrifuging to
that the prism temperature is within 0.1°C of the desired
remove the desiccant. The possibility of changing the compo-
temperature.
sition of the sample by action of the drying agent, by selective
adsorption on the filter, or by fractional evaporation, shall be
12.2 Unlock (if necessary) and open the prism assembly.
considered. (Warning—Volatile hydrocarbon samples are
12.3 Place one or two drops of the sample on the lower
flammable.)
prism face. Close the prism assembly and lock (if necessary).
Turn on the light source. Allow 3min temperature equilibra-
9. Preparation of Apparatus
tion time.
9.1 Therefractometershallbekeptscrupulouslycleanatall
12.4 Look through the eyepiece and observe the field
times. Dust and oil can impair the optical component of the
consisting of a light and dark portion. Follow manufacturer’s
instrument. Thoroughly clean the prism faces with toluene,
instructions to adjust the instrument so that the boundary
followed by n-pentane (see Note 4)(Warning—These mate-
between the light and dark portions of the field is as sharp as
rials are extremely flammable. Harmful if inhaled.Vapors may
possible.
cause flash fire.) using cotton swabs, fresh clean lens tissue, or
12.5 Following manufacturer’s instructions, make any ad-
similar material, in accordance with manufacturer’s instruc-
ditional adjustment until the sharp boundary line intersects the
tions. Do not dry the prism faces by rubbing with dry cotton.
midpoint of the crosshairs superimposed on the field.
9.2 Adjust the thermostat bath/circulator settings or the
12.6 Read the refractive index on the scale. Repeat 12.5 at
electronic temperature control system so that the temperature
least four times, approaching from either side of the sharp
indicatedbytherefractometertemperaturemeasuringdeviceis
boundary line, and average the scale readings.
within0.1°Cofthedesiredvalue.Turnonthelightsourceand
allow the refractometer to equilibrate for 30 min.
12.7 Record and report the average refractive index value.
NOTE 6—The constancy of the prism temperature can be seriously
12.8 If instrument is capable of determining refractive
affected by variations in ambient conditions such as air drafts or changes
inroomtemperature.Reasonableprecautionsshouldbetakentominimize dispersion, change the light source to a light source with
these factors.
different wavelength. Determine the refractive index at the
secondary wavelength following 12.4 – 12.7.
10. Calibration of Refractometer Using Solid Reference
NOTE7—Whendeterminingrefractivedispersion,itisexpectedthatthe
Standard instrument would have been calibrated at both wavelengths used.
10.1 Thoroughly clean the prism faces and surfaces of the
13. Quality Control
solid reference standard (see 7.4.1). Open the prism assembly.
13.1 Confirm the performance of the test procedure by
Apply a drop of 1-bromonaphthalene contact liquid, about
analyzing a quality control (QC) sample, which is stable and
1.5mmindiameter,tothecenterofthepolishedsurfaceofthe
representative of the sample of interest.
solid reference material. Press the reference standard against
13.1.1 When quality control/quality assurance (QC/QA)
thesurfaceoftheprismfacewiththepolishedendtowardsthe
protocols are established in the testing facility, these may be
light source.
used to confirm the reliability of the test result.
10.2 Follow the manufacturer’s instructions on how to
13.1.2 When there are no QC/QA protocols established in
calibrate the instrument using the solid reference standard.
the testing facility, Appendix X4 can be used to provide
10.3 If the observed refractive index differs from the value guidelines in performing this function.
engraved on the solid reference standard by more than 0.0001,
14. Calculation and Report
adjust the refractometer’s scale reading to match the certified
value, following manufacturer’s instructions.
14.1 Report the average refractive index to four decimal
places and the test temperature at which the test was made, for
11. Calibration of the Refractometer Using Liquid
example:
Reference Standards
n 5 x.xxxxat20 °C or n 5 x.xxxxat20 °C (1)
D 589
11.1 UsingtheproceduredescribedinSection12,determine
where D or the 589 signifies
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D1218 − 12 D1218 − 12 (Reapproved 2016)
Standard Test Method for
Refractive Index and Refractive Dispersion of Hydrocarbon
Liquids
This standard is issued under the fixed designation D1218; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*Scope
1.1 This test method covers the measurement of refractive index, accurate to four decimal places or better, of transparent and
light-colored hydrocarbons in the range of 1.3300 to 1.5000 at temperatures from 2020 °C to 30°C30 °C by manual
(optical-mechanical) or automatic (digital) procedure.
1.2 The manual (optical-mechanical) procedure also covers the measurement of refractive dispersion accurate to the fourth
decimal place or better.
NOTE 1—The test method may be suitable for measuring the refractive indices of liquids above 1.5000 and at temperatures both below 20°C20 °C and
above 30°C;30 °C; however, the test method precision may not apply. Verification of the accuracy of such measurements will depend upon the availability
of reliable, certified reference standards that demonstrate the performance of the instrument used under the particular measuring conditions.
1.3 The test method may not be applicable to liquids that are strongly colored, or that have bubble points so near the test
temperature that a reading cannot be obtained before substantial weathering takes place. Liquid color should be limited to No. 4
ASTM Color or lighter, as determined by Test Method D1500.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 WARNING—Mercury has been designated by many regulatory agencies as a hazardous material that can cause central
nervous system, kidney and liver damage. Mercury, or its vapor, may be hazardous to health and corrosive to materials. Caution
should be taken when handling mercury and mercury containing products. See the applicable product Material Safety Data Sheet
(MSDS) for details and EPA’s website—http://www.epa.gov/mercury/faq.htm—for additional information. Users should be aware
that selling mercury and/or mercury containing products into your state or country may be prohibited by law.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. 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.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
D1500 Test Method for ASTM Color of Petroleum Products (ASTM Color Scale)
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-
ment System Performance
D6300 Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products and Lubricants
E1 Specification for ASTM Liquid-in-Glass Thermometers
2.2 ASTM Adjuncts:
Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products and Lubricants, Version 4.0.65
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.04.0D on Physical and Chemical Methods.
Current edition approved Nov. 1, 2012Oct. 1, 2016. Published December 2012November 2016. Originally approved in 1952. Last previous edition approved in 20072012
as D1218–02(2007).D1218 – 12. DOI: 10.1520/D1218-12.10.1520/D1218-12R16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Out of print. No longer available from ASTM International Headquarters.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1218 − 12 (2016)
3. Terminology
3.1 Definitions:
3.1.1 refractive dispersion, n—the difference between the refractive indices of a substance for light of two different wavelengths,
both indices being measured at the same temperature.
3.1.1.1 Discussion—
For convenience in calculations, the value of the difference thus obtained is usually multiplied by 10 000.
3.1.2 refractive index, n—the ratio of the velocity of light (of specified wavelength) in air, to its velocity in the substance under
examination.
3.1.2.1 Discussion—
It may also be defined 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 1.00027, the absolute refractive index of air. The numerical value of refractive index of
liquids varies inversely with both wavelength and temperature.
4. Summary of Test Method
4.1 The refractive index is measured using a high-resolution refractometer of an optical-mechanical or automatic digital type
with the prism temperature accurately controlled. The instrument principle is based on the critical angle concept.
5. Significance and Use
5.1 Refractive index and refractive dispersion are fundamental physical properties, which can be used in conjunction with other
properties to characterize pure hydrocarbons and their mixtures.
PROCEDURE A—MANUAL (OPTICAL-MECHANICAL) PROCEDURE
6. Apparatus
6.1 Refractometer, high-resolution optical-mechanical refractometer of the “Abbe” type with suitable measuring range (1.3300
to 1.5000 or higher) and an accuracy/resolution of 0.0001 or better refractive index.
NOTE 2—Prior to 2001, Test Method D1218 was based on a Bausch & Lomb Refractometer. However, this instrument is no longer manufactured.
Currently available manual refractometers are of the “Abbe” type (critical angle refractometers, see X1.2.3). 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 verification.
6.2 Temperature Control Unit, either an external liquid bath with both heating and cooling capability and pump for maintaining
the indicated prism temperature within 0.1°C,0.1 °C, or an internal electronic temperature control system (such as Peltier system).
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 unit (external or internal) shall have the following control specification:
Stability ± 0.1°C
Uniformity ± 0.1°C
Display Resolution 0.1°C or better
Stability ±0.1 °C
Uniformity ±0.1 °C
Display Resolution 0.1 °C or better
6.3 Temperature Measuring Device, for those apparatus employing mercury in glass thermometer, ASTM Thermometer 17C
having a range from 1919 °C to 27°C,27 °C, and conforming to the requirements of Specification E1. For apparatus using
non-mercury in glass thermometer, a platinum resistance probe, thermocouple, or equivalent temperature sensors are acceptable.
6.4 Light Sources—The following type of light source can be used in conjunction with an optical-mechanical (Abbe type)
refractometer:
6.4.1 Sodium Arc Lamp, Na line at 589 nm.589 nm.
D
6.4.2 Mercury Arc Lamp, Hg line at 546 nm 546 nm or Hg line at 436 nm.436 nm.
c g
6.4.3 Cadmium Arc Lamp, Cd line at 644 nm.644 nm.
C’
6.4.4 Mercury-Cadmium Arc Lamp.
6.4.5 Helium Discharge Lamp.
NOTE 3—Measurement of refractive dispersion requires more than one type of light source.
D1218 − 12 (2016)
6.5 Light Filters—Arc lamps can emit a number of spectral lines that result in multiple-borderlines observed in the
refractometer. Filters can be used to eliminate unwanted lines (borderlines). Depending upon instrument design, the manufacturer
will recommend and supply a suitable filter or adapt a commercially-available filter (for example, interference filter) to suit the
application.
7. Reagents and Materials
7.1 n-Pentane, 95 mol % Minimum Purity, for cleaning the prism faces. (Warning—Flammable. Harmful if inhaled. Vapors
may cause flash fire.)
NOTE 4—Low boiling hydrocarbon fractions with boiling range 5050 °C to 100°C100 °C have also been found to be acceptable.
7.2 Toluene, HPLC Grade, for cleaning the prism faces. (Warning—Flammable. Vapor harmful.)
7.3 1-Bromonaphthalene, 98 mol % Minimum Purity, contact liquid when calibrating with solid reference standard.
(Warning—Toxic when ingested.)
7.4 Primary Reference Materials, for calibrating the instrument.
7.4.1 Solid Reference Standard, with the value of refractive index engraved on its upper face.
7.4.2 Distilled or Deionized Water, conforming to Type II or III of Specification D1193. At 20°C,20 °C, n = 1.3330; at
D
25°C,25 °C, n = 1.3325; and at 30°C,30 °C, n = 1.3319
D D
7.4.3 2,2,4-trimethylpentane, 99 mol % Minimum Purity, at 20°C,20 °C, n = 1.3915; at 25°C,25 °C, n = 1.3890.
D D
7.4.4 Methylcyclohexane, 99 mol % Minimum Purity, at 20°C,20 °C, n = 1.4231; at 25°C,25 °C, n = 1.4206.
D D
7.4.5 Toluene, 99 mol % Minimum Purity, at 20°C,20 °C, n = 1.4969; at 25°C,25 °C, n = 1.4941. (Warning—2,2,4-
D D
trimethylpentane, methylcylcohexane, and toluene are all flammable. Their vapor can be harmful.)
NOTE 5—Other pure materials may be used to calibrate the instrument as primary reference material, as long as they can be obtained in 99 mol %
minimum purity and accurate values of their refractive indices at specific temperatures are available. The precision of the test method (see 15.1 and 24.1)
were obtained using distilled water as the calibrant.
7.5 Secondary Reference Materials, for calibrating the instrument.
7.5.1 Mineral Oil Calibration Standards, measured and certified by suppliers for specific refractive index ranges and
temperatures.
8. Sampling
8.1 A sample of at least 0.5 mL 0.5 mL is required. 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 filtering or centrifuging to remove the desiccant. The possibility of changing the composition of the
sample by action of the drying agent, by selective adsorption on the filter, or by fractional evaporation, shall be considered.
(Warning—Volatile hydrocarbon samples are flammable.)
9. Preparation of Apparatus
9.1 The refractometer shall be kept scrupulously clean at all times. Dust and oil can impair the optical component of the
instrument. Thoroughly clean the prism faces with toluene, followed by n-pentane (see Note 4) (Warning—These materials are
extremely flammable. Harmful if inhaled. Vapors may cause flash fire.) using cotton swabs, fresh clean lens tissue, or similar
material, in accordance with manufacturer’s instructions. Do not dry the prism faces by rubbing with dry cotton.
9.2 Adjust the thermostat bath/circulator settings or the electronic temperature control system so that the temperature indicated
by the refractometer temperature measuring device is within 0.1°C0.1 °C of the desired value. 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 affected by variations in ambient conditions such as air drafts or changes in room
temperature. Reasonable precautions should be taken to minimize these factors.
10. Calibration of Refractometer Using Solid Reference Standard
10.1 Thoroughly clean the prism faces and surfaces of the solid reference standard (see 7.4.1). Open the prism assembly. Apply
a drop of 1-bromonaphthalene contact liquid, about 1.5 mm 1.5 mm in diameter, to the center of the polished surface of the solid
reference material. Press the reference standard against the surface of the prism face with the polished end towards the light source.
10.2 Follow the manufacturer’s instructions on how to calibrate the instrument using the solid reference standard.
10.3 If the observed refractive index differs from the value engraved on the solid reference standard by more than 0.0001, adjust
the refractometer’s scale reading to match the certified value, following manufacturer’s instructions.
11. Calibration of the Refractometer Using Liquid Reference Standards
11.1 Using the procedure described in Section 12, determine the refractive index of any of the Reference Materials specified
in 7.4 or 7.5 for a specific test temperature. If the observed refractive index for the chosen reference material at a specified test
D1218 − 12 (2016)
temperature differs by more than 0.0001 of the listed value, make adjustment to the instrument following manufacturer’s
instructions so that the observed refractive index corresponds to the listed value.
11.2 For optimum accuracy, use a reference material whose refractive index is close to the desired refractive index range and
temperature to calibrate the instrument.
12. Procedure
12.1 Ensure that the prism faces are clean and dry. Check that the prism temperature is within 0.1°C0.1 °C of the desired
temperature.
12.2 Unlock (if necessary) and open the prism assembly.
12.3 Place one or two drops of the sample on the lower prism face. Close the prism assembly and lock (if necessary). Turn on
the light source. Allow 3 min 3 min temperature equilibration time.
12.4 Look through the eyepiece and observe the field consisting of a light and dark portion. Follow manufacturer’s instructions
to adjust the instrument so that the boundary between the light and dark portions of the field is as sharp as possible.
12.5 Following manufacturer’s instructions, make any additional adjustment until the sharp boundary line intersects the
midpoint of the crosshairs superimposed on the field.
12.6 Read the refract
...