|Specific Gravity Problems in Methanol
During the evaluation of the interlaboratory study on Methanol of September 1998, it was found that the IMPCA Methanol Reference Specifications are not clear on this point. As method for this determination of the Specific Gravity of Methanol ASTM D891 is mentioned. However, a laboratory that performs this method fully in accordance with ASTM D891 measures and reports the Apparent Specific Gravity and not the usual Specific Gravity. The difference is only small: 0.0002, but unacceptable as this is not a real measured difference, but a difference caused by definition.
In practice many laboratories are not aware of this peculiarity of ASTM D891 and for ease they use ASTM D4052 for this determination, measuring a density at 20°C. Subsequently, a Specific Gravity is calculated from the measured density. However, the Apparent Specific Gravity should be calculated and reported in order to get a result that will be comparable with the result of ASTM D891.