ASTM D1747 Standard Test Method for Refractive Index of Viscous Materials
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 a 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, conforming to Thermometer 21C for determinations at 80C or Thermometer 22C for determinations at 100C as given in Specification E 1 are recommended. 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 adeuate 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, 0.0005 in. (0.013 mm) thickness, and precision potentiometer. The thermocouple is calibrated by immersing to a depth of 1 in. (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.

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.

NOTE 6 - 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.

NOTE 7 - Warning: Flammable. Vapor harmful.

8. Reference Standards
8.1 Primary Liquid Standards - The 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 can be obtained from API Standard Reference Office, Carnegie-Mellon University, Pittsburgh, PA 15213.

8.2 Working Standards - For working standard hydrocarbons, reasonably well purified samples of n-hexadecane, transdecahydronaphthalene, 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.

NOTE 8 - Caution: Both primary and 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.