ISO 12185 Crude petroleum and petroleum products - Determination of density - Oscillating U-tube method
5 Apparatus
5.1 Density meter, capable, once calibrated, of determining density with a resolution of +/- 0.1 kg/m3 or better.
NOTE 3 Meters commonly display two forms of digital result, either a density value or the period of oscillation from which density can be calculated.
NOTE 4 Research has shown that the density meter may show a bias of up effects. Users should ascertain whether a viscosity correction is required by checking the result using a pyknometer method such as that given in ISO 3838. Alternatively, viscosity effects can be minimized by using certified calibration standards of chemical characteristics and viscosity similar to that of the sample under test [3].
NOTE 5 Problems have been experienced with certain density meters due to condensation gathering on the cell sensors and electronics when the cell temperature is held below the dew-point of the ambient air. If there is risk of this occurring, the surrounding air should be kept dry.
5.2 Circulating constant-temperature bath, if required (see 9.1.2), capable of maintaining the temperature of the circulating liquid to within +/- 0.05 °C of the required temperature.
5.3 Calibrated temperature sensor, capable of measuring the temperature of the cell to an accuracy of at least +/- 0.10 °C.
The rate of energy transfer across the cell is low and therefore care should be taken to use sensors with very fine leads in order to minimize heat transfer in or out of the cell along the leads.
5.4 Homogenizer, suitable for the sample and sample container, and capable of producing homogeneous subsamples for test (see clause 8); a high speed shear or static mixer, or other type as appropriate.
6 Reagents
Unless otherwise stated, use only reagents of recognized analytical grade.
6.1 Flushing solvent.
NOTE 6 Any solvent may be used provided that it is capable of producing a clean dry cell.
6.2 Ammonium peroxydisulfate, solution in concentrated sulfuric acid, 8 g/l.
WARNING - Ammonium peroxydisulfate is a strong oxidizing agent.
6.3 Calibration fluids.
A minimum of two calibration fluids are needed to calibrate the cell. They shall be chosen so that their densities bracket the density of the sample under test. The density of the calibration fluids shall be traceable to recognized national standards or based on internationally accepted values.
When water and/or air are used, the requirements of 6.3.1 and 6.3.2 shall be met.
6.3.1 Water, conforming to ISO 3696 grade 2 or better.
Prior to use, pass the water through a 0.45 μm filter, and remove dissolved air by first boiling and then cooling. Once de-aired, handle the water carefully so as to minimize the amount of air redissolved.
Obtain the water density from the table given in Appendix G of IP "Standard methods for analysis and testing of petroleum and related products". On publication of the BIPM tables (see clause 2), the values for density of water given therein shall be used.
NOTE 7 The density of water at various temperatures given in Appendix G has been prepared by the Institute of Petroleum, in order to provide a source for the density of water based on the International Temperature Scale 1990, whilst the work to produce new water-density tables, based on new water data, is carried out by BIPM.
6.3.2 Air.
Use the values of the density of air given in Appendix H of IP "Standard methods for analysis and testing of petroleum and related products". On publication of the BIPM tables (see clause 2). the values for density of ambient air given therein shall be used.
NOTE 8 The density of ambient air at various temperatures given in Appendix H has been prepared by the Institute of Petroleum, in order to provide a source for the density of ambient air based on the International Temperature Scale 1990, whilst work to produce new density of ambient air tables is carried out by BIPM.
6.4 Water, conforming to ISO 3696 Grade 3.
