ASTM D1747-09(2014)
(Test Method)Standard Test Method for Refractive Index of Viscous Materials
Standard Test Method for Refractive Index of Viscous Materials
SIGNIFICANCE AND USE
5.1 Refractive index is a fundamental physical property that can be used in conjunction with other properties to characterize pure hydrocarbons and their mixtures.
5.2 The use of refractive index in correlative methods for the determination of the gross composition of viscous oils and waxes often requires its measurement at elevated temperatures.
SCOPE
1.1 This test method covers the measurement of refractive indexes, accurate to two units in the fourth decimal place, of transparent and light-colored viscous hydrocarbon liquids and melted solids that have refractive indexes in the range between 1.33 and 1.60, and at temperatures from 80 to 100°C. Temperatures lower than 80°C can be used provided that the melting point of the sample is at least 10°C below the test temperature.
1.2 This test method is not applicable, within the accuracy stated, to liquids having colors darker than ASTM Color No. 4, ASTM color as determined by Test Method D1500, to liquids which smoke or vaporize readily at the test temperature, or to solids melting within 10°C of the test temperature.
Note 1: The instrument can be successfully used for refractive indices above 1.60; but since certified liquid standards for ranges above 1.60 are not yet available, the accuracy of measurement under these conditions has not been evaluated.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 Warning—Mercury has been designated by EPA and many state 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 or mercury-containing products, or both, in your state may be prohibited by state law.
1.5 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.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D1747 − 09 (Reapproved 2014)
Standard Test Method for
Refractive Index of Viscous Materials
This standard is issued under the fixed designation D1747; 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 priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1.1 This test method covers the measurement of refractive
indexes, accurate to two units in the fourth decimal place, of
2. Referenced Documents
transparent and light-colored viscous hydrocarbon liquids and
2.1 ASTM Standards:
meltedsolidsthathaverefractiveindexesintherangebetween
1.33 and 1.60, and at temperatures from 80 to 100°C. Tem- D362SpecificationforIndustrialGradeToluene(Withdrawn
1989)
peratures lower than 80°C can be used provided that the
melting point of the sample is at least 10°C below the test D841Specification for Nitration Grade Toluene
D1500Test Method forASTM Color of Petroleum Products
temperature.
(ASTM Color Scale)
1.2 This test method is not applicable, within the accuracy
D6299Practice for Applying Statistical Quality Assurance
stated,toliquidshavingcolorsdarkerthanASTMColorNo.4,
and Control Charting Techniques to Evaluate Analytical
ASTM color as determined by Test Method D1500, to liquids
Measurement System Performance
which smoke or vaporize readily at the test temperature, or to
E1Specification for ASTM Liquid-in-Glass Thermometers
solids melting within 10°C of the test temperature.
E77Test Method for Inspection and Verification of Ther-
NOTE1—Theinstrumentcanbesuccessfullyusedforrefractiveindices
mometers
above 1.60; but since certified liquid standards for ranges above 1.60 are
notyetavailable,theaccuracyofmeasurementundertheseconditionshas
3. Terminology
not been evaluated.
3.1 Definitions:
1.3 The values stated in SI units are to be regarded as
3.1.1 refractive index—the ratio of the velocity of light (of
standard. No other units of measurement are included in this
specified wavelength) in air, to its velocity in the substance
standard.
under examination. The relative index of refraction is defined
1.4 Warning—Mercury has been designated by EPA and
as the sine of the angle of incidence divided by the sine of the
many state agencies as a hazardous material that can cause
angle of refraction, as light passes from air into the substance.
central nervous system, kidney, and liver damage. Mercury, or
If absolute refractive index (that is, referred to vacuum) is
its vapor, may be hazardous to health and corrosive to
desired, this value should be multiplied by the factor 1.00027,
materials.Cautionshouldbetakenwhenhandlingmercuryand
the absolute refractive index of air. The numerical value of
mercury-containing products. See the applicable product Ma-
refractive index of liquids varies inversely with both wave-
terial Safety Data Sheet (MSDS) for details and EPA’s website
length and temperature.
(http://www.epa.gov/mercury/faq.htm) for additional informa-
tion. Users should be aware that selling mercury or mercury-
4. Summary of Test Method
containingproducts,orboth,inyourstatemaybeprohibitedby
4.1 Therefractiveindexnormallyismeasuredbythecritical
state law.
angle method using monochromatic light from a sodium lamp.
1.5 This standard does not purport to address all of the
The instrument is previously adjusted by means of calibration
safety concerns, if any, associated with its use. It is the
obtained with certified liquid standards.
responsibility of the user of this standard to establish appro-
1 2
This test method is under the jurisdiction of ASTM Committee D02 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Petroleum Products, Liquid Fuels, and Lubricantsand is the direct responsibility of contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Subcommittee D02.04.0D on Physical and Chemical Methods. Standards volume information, refer to the standard’s Document Summary page on
CurrenteditionapprovedJune1,2014.PublishedJuly2014.Originallyapproved the ASTM website.
in 1960. Last previous edition approved in 2009 as D1747–09. DOI: 10.1520/ The last approved version of this historical standard is referenced on
D1747-09R14. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1747 − 09 (2014)
TABLE 1 Primary Liquid Standards liquid should pass the thermometer on leaving, not on entering, the prism
assembly.
Approximate Refractive Index,
Certified Standard
n
D
6.4 Thermocouple, copper-constantanfoiltype,0.013-mm
n-Hexadecane 1.41
thickness, and precision potentiometer. The thermocouple is
trans-Decahydronaphthalene 1.44
calibrated by immersing to a depth of 25 mm in a circulating
1-Methylnaphthalene 1.59
liquidthermostatandcomparingwithathermometerofknown
accuracy.
6.5 Light Source, Sodium Arc Lamp—The light source shall
5. Significance and Use
be a sodium arc lamp, which shall be used only after the
5.1 Refractiveindexisafundamentalphysicalpropertythat removalofAmicicompensatingprisms,ifthereareanypresent
canbeusedinconjunctionwithotherpropertiestocharacterize in the instrument.
pure hydrocarbons and their mixtures.
NOTE5—Ifthefielddivisionasobservedin12.2shiftswhentheAmici
prismisrotated,theprismshouldberemovedtoavoidincorrectreadings.
5.2 The use of refractive index in correlative methods for
the determination of the gross composition of viscous oils and
7. Solvents
waxesoftenrequiresitsmeasurementatelevatedtemperatures.
7.1 Cleaning Solvent, any suitable solvent capable of clean-
6. Apparatus
ing the apparatus as described in Section 10. 1,1,1, Trichlo-
roethane has been found suitable to use. (Warning—Harmful
6.1 Refractometer, precision Abbé-type, having a range in
if inhaled. High concentration can cause unconsciousness or
refractive index from 1.30 to 1.63. Other instruments reading
death. Contact can cause skin irritation and dermatitis.)
to at least four decimal places may be used.
7.2 Toluene, conforming to Specification D362 or Specifi-
NOTE 2—When other instruments are used, follow the manufacturer’s
cation D841.(Warning—Flammable. Vapor harmful.)
instructions for operation, maintenance, calibration, and analysis. For
accepting the instrumentation for use, analysis of an NIST traceable
8. Reference Standards
certified material to ensure accuracy should be performed.
6.2 Thermostat and Circulating Pump,capableofmaintain- 8.1 Primary Liquid Standards—Organic liquids listed in
ing the indicated prism temperature constant within 0.02°C. Table 1, with the values of their refractive indexes for the
Thecirculatingfluidconsistsofethyleneglycoloramixtureof sodium D line certified at 20, 25, 30, 80, and 100°C.
30 to 40 volume% of glycerin in water flowing through the (Warning —Primary standards are combustible.)
prisms at a fixed rate of at least 2.5 L/min. For work at 100°C,
8.2 Working Standards—For working standard
properly controlled wet steam is also suitable.
hydrocarbons, reasonably well purified samples of
n-hexadecane, trans -decahydronaphthalene, and
NOTE 3—The constancy of the prism temperature can be seriously
affected by variations in ambient conditions, such as air drafts or changes
1-methylnaphthalene may be used. Their exact values are
inroomtemperature.Reasonableprecautionsshouldbetakentominimize
determined by comparison with standard samples of the same
these factors. Insulation placed on the thermostat, circulating fluid lines,
hydrocarbons having certified values of refractive index.
and refractometer also may prove to be helpful.
(Warning—Working standards are combustible.)
6.3 Thermometers, or Equivalent Temperature Measuring
Devices, conforming to Thermometer 21C for determinations
9. Sample
at 80°C or Thermometer 22C for determinations at 100°C as
9.1 Asampleofatleast0.5mLisrequired.Thesampleshall
given in Specification E1 are recommended. See Test Method
be free of suspended solids, water, or other materials that tend
E77 for guidance on inspection and verification of mercury in
to scatter light. Water can be removed from hydrocarbons by
glassthermometers.Equivalenttemperaturemeasuringdevices
treatment with calcium chloride followed by filtering or
should have the same accuracy and resolution as Thermom-
centrifugingtoremovethedesiccant.Thepossibilityofchang-
eters 21C and 22C.
ing the composition of a sample by action of the drying agent,
6.3.1 In case of dispute, the test method shall be carried out
by selective adsorption on the filter, or by fractional
using the specified mercury in glass thermometer.
evaporation, shall be considered.
6.3.2 The temperature measuring device, suitably
calibrated, shall be positioned to measure the temperature of
10. Preparation of Apparatus
theprism(seeNote4)withinanappropriateholder.Theholder
10.1 The refractometer shall be kept scrupulously clean at
shall provide for adequate immersion of the temperature
all times. Dust and oil, if allowed to accumulate on any part of
measuringdeviceandforfreeflowofthecirculatingfluid.The
the instrument, will find its way into the moving parts, causing
temperature measuring device holder assembly shall be insu-
lated with a suitable material, such as cork.
The sole source of supply of the apparatus known to the committee at this time
NOTE 4—In the precision Abbé type refractometer, the thermostating
is RdF Corp., 23 ElmAvenue, Hudson, NH 03051. If you are aware of alternative
suppliers, please provide this information to ASTM International Headquarters.
Your comments will receive careful consideration at a meeting of the responsible
4 1
The Abbé-type precision refractometer is no longer available but may be technical committee , which you may attend.
obtainablefrominstrumentexchangesorusedequipmentsuppliers.Otherprecision Available from API Standard Reference Office, Carnegie-Mellon University,
refractometers may be suitable, but they have not as yet been tested cooperatively. Pittsburgh, PA15213.
D1747 − 09 (2014)
wear and eventual misalignment. If permitted to collect on the 25, 30, 80, and 100°C against temperature and drawing a
prism, dust will dull the polish, resulting in hazy lines. smooth curve between the points.
10.2 Thoroughly clean the prism faces with fresh clean lens 11.6 Precautions—In using pure liquids for calibration or
tissue or surgical grade absorbent cotton saturated with a checking of calibration of an Abbé-type refractometer, the
suitable solvent. Pass the swab very lightly over the surface following precautions should be observed:
untilitshowsnotendencytostreak.Repeattheprocedurewith
11.6.1 Before inserting the hydrocarbon calibrating liquids,
a fresh swab and solvent until both the glass and adjacent the prisms should be flushed with solvents and cleaned as
polished metal surfaces are clean. Do not dry the prism faces
described in 8.2. It is advisable to preheat the solvent before
by rubbing with dry cotton. use to minimize thermal shock to the prism. This should be
followed by several such flushings with the test liquid and
10.3 Adjust the thermostat so that the temperature as indi-
wiping with lens paper.After such cleaning, a reading with the
cated by the thermocouple inserted between the prism faces
test liquid should be taken as described in Section 11. This
andwetwithoiliswithin0.2°Cofthedesiredtesttemperature.
should be followed by another flushing with the test liquid
Thistemperatureistobeheldconstanttowithin0.02°Cduring
beforetakinganotherreadingofthetestliquidintheprescribed
the test. Observe and record the thermometer reading corre-
manner. The prisms cannot be considered free from contami-
sponding to the test temperature. Turn on the sodium arc lamp
nating substances until two such determinations on the test
and allow it to warm up for 30 min.
liquid agree within the limits given in 11.6.2.
11.6.2 In setting the edge of the field on the cross hairs,
11. Standardization with Reference Liquids
readings should be taken in pairs, approaching the alidade
11.1 Introduce a sample of the API Standard trans-
setting from one direction only as recommended by the
decahydronaphthalene to the prism which is adjusted to the
manufacturer. Several such sets will probably be necessary
chosen test temperature of 80 or 100°C, turn the telescope
before satisfactory agreement is obtained. Satisfactory agree-
adjustment screw until a refractive index scale reading corre-
ment is 0.00005 to 0.0001.
sponding to the certified refractive index for trans-
11.6.3 For results of highest accuracy, the calibration with
decahydronaphthalene is observed, and adjust the instrument
hydrocarbons of known properties should be made immedi-
according to the instructions given by the manufacturer until
ately before the determination on the sample.
the sharp boundary between the light and dark portions of the
11.6.4 Fluctuationsinambienttemperaturesshouldbemini-
field passes through the intersection of the cross hairs of the
mized as much as possible during the test.
telescope.
11.2 Check the accuracy of this setting by loading a fresh
12. Procedure
sample of trans-decahydronaphthalene and measure its refrac-
12.1 Thoroughly clean the prism faces as described in 10.2.
tive index at the test temperature following the procedure
Adjust the thermostat so that the temperature indicated by the
described in Section 12. If the value for the refractive index
thermocouple placed between the faces of the closed prism
differs from the certified value by 0.0001 or more units, then
(loaded with oil) is within 0.2°C of the desired value. The
repeat the procedure given in 11.1 until a satisfactory check is
thermocouple is used for establishing the correct temperature
obtained.
level and may be removed during measurements of refractive
11.3 Measure the refractive index of API Standard index. The observed reading of the thermometer at this
n-hexadecane and 1-methylnaphthalene at the test temperature temperature must be held constant to 0.02°C in the measure-
following the procedure described in Section 12. ments to follow.
11.4 Construct a calibration curve for use at the chosen test 12.2 Close the prism box and let it stand for 3 to 5 min to
temperature. Plot the difference between the observed refrac- ensure temperature equilibrium between the prisms and the
tive index for n-hexadecane and its certified value along the circulating bath liquid. Melt samples which are normall
...
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: D1747 − 09 D1747 − 09 (Reapproved 2014)
Standard Test Method for
Refractive Index of Viscous Materials
This standard is issued under the fixed designation D1747; 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 indexes, accurate to two units in the fourth decimal place, of
transparent and light-colored viscous hydrocarbon liquids and melted solids that have refractive indexes in the range between 1.33
and 1.60, and at temperatures from 80 to 100°C. Temperatures lower than 80°C can be used provided that the melting point of the
sample is at least 10°C below the test temperature.
1.2 This test method is not applicable, within the accuracy stated, to liquids having colors darker than ASTM Color No. 4,
ASTM color as determined by Test Method D1500, to liquids which smoke or vaporize readily at the test temperature, or to solids
melting within 10°C of the test temperature.
NOTE 1—The instrument can be successfully used for refractive indices above 1.60; but since certified liquid standards for ranges above 1.60 are not
yet available, the accuracy of measurement under these conditions has not been evaluated.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 Warning—Mercury has been designated by EPA and many state 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 or mercury-containing products, or both, in your state may be prohibited by state law.
1.5 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:
D362 Specification for Industrial Grade Toluene (Withdrawn 1989)
D841 Specification for Nitration Grade Toluene
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
E1 Specification for ASTM Liquid-in-Glass Thermometers
E77 Test Method for Inspection and Verification of Thermometers
3. Terminology
3.1 Definitions:
3.1.1 refractive index—the ratio of the velocity of light (of specified wavelength) in air, to its velocity in the substance under
examination. The relative index of refraction is 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. If absolute refractive index (that is, referred to vacuum) is desired, this value
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products Products, Liquid Fuels, and Lubricantsand is the direct responsibility of
Subcommittee D02.04.0D on Physical and Chemical Methods.
Current edition approved Oct. 1, 2009June 1, 2014. Published October 2009July 2014. Originally approved in 1960. Last previous edition approved in 20042009 as
ε1
D1747–99(2004)D1747 .–09. DOI: 10.1520/D1747-09.10.1520/D1747-09R14.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
*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
D1747 − 09 (2014)
TABLE 1 Primary Liquid Standards
Approximate Refractive Index,
Certified Standard
n
D
n-Hexadecane 1.41
trans-Decahydronaphthalene 1.44
1-Methylnaphthalene 1.59
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 normally is measured by the critical angle method using monochromatic light from a sodium lamp. The
instrument is previously adjusted by means of calibration obtained with certified liquid standards.
5. Significance and Use
5.1 Refractive index is a fundamental physical property that can be used in conjunction with other properties to characterize
pure hydrocarbons and their mixtures.
5.2 The use of refractive index in correlative methods for the determination of the gross composition of viscous oils and waxes
often requires its measurement at elevated temperatures.
6. Apparatus
6.1 Refractometer, precision Abbé-type, having a range in refractive index from 1.30 to 1.63. Other instruments reading to at
least four decimal places may be used.
NOTE 2—When other instruments are used, follow the manufacturer’s instructions for operation, maintenance, calibration, and analysis. For accepting
the instrumentation for use, analysis of an NIST traceable certified material to ensure accuracy should be performed.
6.2 Thermostat and Circulating Pump, capable of maintaining the indicated prism temperature constant within 0.02°C. The
circulating fluid consists of ethylene glycol or a mixture of 30 to 40 volume % of glycerin in water flowing through the prisms
at a fixed rate of at least 2.5 L/min. For work at 100°C, properly controlled wet steam is also suitable.
NOTE 3—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. Insulation placed on the thermostat, circulating fluid lines, and
refractometer also may prove to be helpful.
6.3 Thermometers, or Equivalent Temperature Measuring Devices, conforming to Thermometer 21C for determinations at 80°C
or Thermometer 22C for determinations at 100°C as given in Specification E1 are recommended. See Test Method E77 for
guidance on inspection and verification of mercury in glass thermometers. Equivalent temperature measuring devices should have
the same accuracy and resolution as Thermometers 21C and 22C.
6.3.1 In case of dispute, the test method shall be carried out using the specified mercury in glass thermometer.
6.3.2 The temperature measuring device, suitably calibrated, shall be positioned to measure the temperature of the prism (see
Note 4) within an appropriate holder. The holder shall provide for adequate immersion of the temperature measuring device and
for free flow of the circulating fluid. The temperature measuring device holder assembly shall be insulated with a suitable material,
such as cork.
NOTE 4—In the precision Abbé type refractometer, the thermostating liquid should pass the thermometer on leaving, not on entering, the prism
assembly.
6.4 Thermocouple, copper-constantan foil type, 0.013-mm thickness, and precision potentiometer. The thermocouple is
calibrated by immersing to a depth of 25 mm in a circulating liquid thermostat and comparing with a thermometer of known
accuracy.
6.5 Light Source, Sodium Arc Lamp—The light source shall be a sodium arc lamp, which shall be used only after the removal
of Amici compensating prisms, if there are any present in the instrument.
NOTE 5—If the field division as observed in 12.2 shifts when the Amici prism is rotated, the prism should be removed to avoid incorrect readings.
The Abbé-type precision refractometer is no longer available but may be obtainable from instrument exchanges or used equipment suppliers. Other precision
refractometers may be suitable, but they have not as yet been tested cooperatively.
The sole source of supply of the apparatus known to the committee at this time is RdF Corp., 23 Elm Avenue, Hudson, NH 03051. If you are aware of alternative suppliers,
please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee ,
which you may attend.
D1747 − 09 (2014)
7. Solvents
7.1 Cleaning Solvent, any suitable solvent capable of cleaning the apparatus as described in Section 10. 1,1,1, Trichloroethane
has been found suitable to use. (Warning—Harmful if inhaled. High concentration can cause unconsciousness or death. Contact
can cause skin irritation and dermatitis.)
7.2 Toluene, conforming to Specification D362 or Specification D841. (Warning—Flammable. Vapor harmful.)
8. Reference Standards
8.1 Primary Liquid Standards—Organic liquids listed in Table 1, with the values of their refractive indexes for the sodium D
line certified at 20, 25, 30, 80, and 100°C. (Warning —Primary standards are combustible.)
8.2 Working Standards—For working standard hydrocarbons, reasonably well purified samples of n-hexadecane, trans
-decahydronaphthalene, and 1-methylnaphthalene may be used. Their exact values are determined by comparison with standard
samples of the same hydrocarbons having certified values of refractive index. (Warning—Working standards are combustible.)
9. Sample
9.1 A sample of at least 0.5 mL is required. The sample shall be free of suspended solids, water, or other materials that tend
to scatter light. 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 a sample by action of the drying agent, by selective
adsorption on the filter, or by fractional evaporation, shall be considered.
10. Preparation of Apparatus
10.1 The refractometer shall be kept scrupulously clean at all times. Dust and oil, if allowed to accumulate on any part of the
instrument, will find its way into the moving parts, causing wear and eventual misalignment. If permitted to collect on the prism,
dust will dull the polish, resulting in hazy lines.
10.2 Thoroughly clean the prism faces with fresh clean lens tissue or surgical grade absorbent cotton saturated with a suitable
solvent. Pass the swab very lightly over the surface until it shows no tendency to streak. Repeat the procedure with a fresh swab
and solvent until both the glass and adjacent polished metal surfaces are clean. Do not dry the prism faces by rubbing with dry
cotton.
10.3 Adjust the thermostat so that the temperature as indicated by the thermocouple inserted between the prism faces and wet
with oil is within 0.2°C of the desired test temperature. This temperature is to be held constant to within 0.02°C during the test.
Observe and record the thermometer reading corresponding to the test temperature. Turn on the sodium arc lamp and allow it to
warm up for 30 min.
11. Standardization with Reference Liquids
11.1 Introduce a sample of the API Standard trans-decahydronaphthalene to the prism which is adjusted to the chosen test
temperature of 80 or 100°C, turn the telescope adjustment screw until a refractive index scale reading corresponding to the certified
refractive index for trans-decahydronaphthalene is observed, and adjust the instrument according to the instructions given by the
manufacturer until the sharp boundary between the light and dark portions of the field passes through the intersection of the cross
hairs of the telescope.
11.2 Check the accuracy of this setting by loading a fresh sample of trans-decahydronaphthalene and measure its refractive
index at the test temperature following the procedure described in Section 12. If the value for the refractive index differs from the
certified value by 0.0001 or more units, then repeat the procedure given in 11.1 until a satisfactory check is obtained.
11.3 Measure the refractive index of API Standard n-hexadecane and 1-methylnaphthalene at the test temperature following the
procedure described in Section 12.
11.4 Construct a calibration curve for use at the chosen test temperature. Plot the difference between the observed refractive
index for n-hexadecane and its certified value along the ordinate against the refractive index level along the abscissa. Also plot the
difference between the observed and certified refractive indices for 1-methylnaphthalene in the same manner. Draw a straight line
from the point representing the deviation found for n-hexadecane to zero at the certified refractive index of trans-
decahydronaphthalene. Likewise, draw a straight line from this same zero point to the deviation found for 1-methylnaphthalene.
11.5 If it is desired to measure the refractive index of samples at a temperature other than 80 or 100°C, obtain calibration data
by repeating 11.1 – 11.4 at this desired temperature. Determine the refractive indices for the API Standard compounds,
n-hexadecane, trans-decahydronaphthalene, and 1-methylnaphthalene at the desired temperature by plotting the certified refractive
indices at 20, 25, 30, 80, and 100°C against temperature and drawing a smooth curve between the points.
Available from API Standard Reference Office, Carnegie-Mellon University, Pittsburgh, PA 15213.
D1747 − 09 (2014)
11.6 Precautions—In using pure liquids for calibration or checking of calibration of an Abbé-type refractometer, the following
precautions should be observed:
11.6.1 Before inserting the hydrocarbon calibrating liquids, the prisms should be flushed with solvents and cleaned as described
in 8.2. It is advisable to preheat the solvent before use to minimize thermal shock to the prism. This should be followed by several
such flushings with the test liquid and wiping with lens paper. After such cleaning, a reading with the test liquid should be ta
...
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