Handbook of Solvents - George Wypych - ChemTech - Ventech!

1066 George Wypych
15.1.26 REFRACTIVE INDEX
Refractive index is measured by a standard method. 104 It covers transparent and light colored
liquids having a refractive index in the range from 1.33 to 1.50. The refractive index is
the ratio of light velocity of a specified wavelength in air to its velocity in the substance under
evaluation. The refractive dispersion is the difference between refractive indices for
light of two different wavelengths. This value is usually multiplied by 10,000. The method
uses a Bausch & Lomb refractometer equipped with a thermostat and with a circulating bath
to control the sample temperature with a precision of 0.2 o C. Several light sources can be
used, including the sodium arc lamp, mercury light lamp, and hydrogen or helium discharge
lamp. Light sources are equipped with filters which transmit a specific spectral line. Standardization
of equipment is done using a solid reference standard or using liquids standards
such as 2,2,4-trimethylpentane (1.39), methylcyclohexane (1.42), or toluene (1.49).
15.1.27 RESIDUAL SOLVENTS
Residual solvents may cause odor, off-taste, blocking, and an increased degradation rate in
outdoor exposures. A single standard test method has been developed to determine residual
solvent levels and it is primarily used for the evaluation of flexible barrier materials. 105 The
method is based on gas chromatography. The specimen of the barrier material is enclosed in
a container and heated to vaporize the retained solvents into the head space. The vapor from
the head space is taken by a gas syringe and injected into a gas chromatograph. The recovery
of solvents is compared by the means of response factor which is a peak intensity of the
detector in response to a given volume of injected sample. Response factors of different
solutions vaporized in the test containers are compared. Round robin tests have
demonstrated that this method has a coefficient of variation between laboratories of ±15%.
The method does not specify the detector or the columns. Before a flexible barrier material
is analyzed, the optimum heating time to recover volatilized solvents is determined.
15.1.28 SOLUBILITY
Solvent power of a hydrocarbon solvents is determined by kauri-butanol value. 106 The
method applies to solvents having a boiling point above 40 o C and a dry point below 300 o C.
The method is most frequently used to evaluate solvents for applications in paints and lacquers.
The kauri-butanol value is the volume of solvent required to produce a defined degree
of turbidity when added to 20 g of a standard solution of kauri resin in n-butanol (400 g
of resin in 2000 g of solvent). High kauri value indicates a relatively strong dissolving
power. The method is standardized using 105±5 ml of toluene.
The solubility of common gases in hydrocarbon liquids is determined to meet requirements
of aerospace industry. 107 This test method is based on the Clausius-Clapeyron equation,
Henry’s law, and the perfect gas law. The results are important in the lubrication of gas
compressors where dissolved gas may cause erosion due to cavitation. In fuels, dissolved
gases may cause interruption of fuel supply and foaming in tank. The liquid density is determined
experimentally. Using this density, the Ostwald coefficient is taken from a chart and
used for the calculation of the Bunsen coefficient (solubility of gas). The solubility of the
gas or mixture of gases and Henry’s law constant are also calculated.
15.1.29 SOLVENT PARTITIONING IN SOILS
A procedure is available to determine partitioning organic chemicals between water and soil
or sediment. 108 By measuring sorption coefficients for specific solids, a single value is
obtained which can be used to predict partitioning under a variety of conditions. The