ASTM D1298 for density of crude petroleum and liquid petroleum products by hydrometer method
11. Calculation
11.1 Apply any relevant thermometer corrections to the temperature reading observed in 10.6 and 10.13 and record the average of those two temperatures to the nearest 0.1°C.
11.2 For opaque samples, apply the relevant meniscus correction given in Table 1 to the observed hydrometer reading (10.12.2) as hydrometers are calibrated to be read at the principal surface of the liquid.
NOTE 8 - The meniscus correction for a particular hydrometer in use is determined by observing the maximum height above the principal surface of the liquid to which liquid rises on the hydrometer scale when the hydrometer in question is immersed in a transparent liquid having a surface tension similar to that of the sample under test. For hydrometers specified in this test method, the corrections in Table 1 are approximate.
11.3 Apply any hydrometer correction to the observed reading and record the corrected hydrometer scale reading to the nearest 0.1 kg/m3 in density, 0.0001 g/mL, kg/L or relative density, or 0.1°API.
11.4 If the hydrometer has been calibrated at a temperature other than the reference temperature, use the equation below to correct the hydrometer scale reading:
11.5 Convert the corrected hydrometer scale reading to density, relative density or API gravity using the appropriate parts of the Petroleum Measurement Tables referenced in Guide D 1250 according to the nature of the materials under test. Table 3 gives some examples of relevant table numbers in the Petroleum Measurement Tables.
11.5.1 The strictly correct procedure for the conversion is to use the computer implementation procedures contained in the Petroleum Measurement Tables and not the printed tables. If the printed tables are used, ensure that all errata discovered since original publication have been included in the version used. The tables include corrections for soda-lime glass expansion and contraction of the hydrometer over the temperature range, and thus the observed hydrometer reading is added directly after correction (11.2-11.4) as necessary.
11.5.2 To convert densities expressed in kg/m3 to densities expressed in g/mL or kg/L, divide by 10(3).
11.5.3 To convert hydrometer readings from one unit to another, Tables 51 (density at 15°C), 21 (relative density at 60/60°F) or 3 (API gravity), referenced in Guide D 1250, are appropriate.