GB/T 2013-2010 Determination of density of liquid petrochemical products

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Incomplete source card: Sections 10, 11, 12, 13, 14 are absent from the available source. Only available content is translated; source completion is pending.

Card type: Test method

1. Method number / full name / English name / replacement relationship

• Standard number: GB/T 2013—2010
• Chinese name: Determination of density of liquid petrochemical products
• English name: Standard test method for density of liquid petrochemical products
• Replacement relationship: replaces GB/T 2013—1980 "Determination of density of benzene products"
• Degree of consistency: non-equivalent to ASTM D891:95 "Determination of apparent specific gravity of liquid chemical industrial products"
• Contains three test methods:
  • Test method A—— hydrometer method
  • Test method B——U type vibrating tube method
  • Test method C—— pycnometer method
• Publication/implementation: published on 2011-01-10, implemented on 2011-05-01
• Previous versions: GB/T 2013—1980

2. Scope of application and non-applicability

• 1.1 This standard specifies three test methods for determining the density of liquid petrochemical products using a hydrometer, a U type vibrating tube, and a pycnometer.
• 1.2 Test method A (hydrometer method): suitable for determining the density of easily flowing transparent liquids; for viscous liquids that do not flow easily, a constant-temperature bath may be used to determine at a temperature above room temperature; it can also be used for opaque liquids, but the reading method differs from that for transparent liquids.
• 1.3 Test method B (U type vibrating tube method): suitable for petrochemical products that can be handled as a single-phase liquid at the test temperature and test pressure; suitable for liquids of any vapor pressure, but measures must be taken to ensure that the sample remains single-phase throughout handling and determination, with no loss of light components and no change in composition and density.
• 1.4 Test method C (pycnometer method): suitable for density measurement of petrochemical products that can be handled as liquids at the test temperature and test pressure.
  • Capillary-stoppered pycnometer: not suitable for liquids with an initial boiling point lower than 40 °C.
  • Graduated double-capillary pycnometer: suitable for precise measurement of the density of all liquid petrochemical products except relatively viscous products, particularly suitable for liquids with only a small amount of sample, but limited to liquids with a kinematic viscosity at the test temperature not exceeding 50 mm²/s.
• Hydrometer method measurement range: 600 kg/m³～1 100 kg/m³ (the source text writes 600 kg/m°～1 100 kg/m°, the unit is suspected to be source-text extraction noise, requires confirmation against the source standard (source-text extraction)).

3. Method principle

• 5.1 Summary of the hydrometer method: bring the test sample to the specified temperature, pour it into a density cylinder at approximately the same temperature, place a suitable hydrometer into the sample whose temperature has been adjusted, and let it stand; after temperature equilibrium, read the hydrometer reading and the sample temperature, and convert to density or standard density as needed. If necessary, place the cylinder in a constant-temperature bath to avoid excessive temperature fluctuations.
• 6.1 Summary of the U type vibrating tube method: inject a small amount of sample (generally less than 1 mL) into a temperature-controllable sample tube, record the vibration frequency or period, and calculate the sample density using the sample tube constant obtained in advance; the sample tube constant is determined from the vibration frequency when the sample tube is filled with a calibration liquid of known density. Newer instruments directly display the density value after the sample is injected into the sample tube.
• 7.1.1 Summary of the capillary-stoppered pycnometer method: fill the pycnometer with the test sample, bring to constant temperature at the determination temperature, and weigh the mass of the sample; calculate the sample density by dividing this mass by the ratio of the mass of water in the pycnometer previously measured at the same temperature (water value) to its density.
• 7.1.2 Summary of the graduated double-capillary pycnometer method: calibrate the two-arm scale of the pycnometer with water, and plot the apparent mass in air of the water contained in the pycnometer against the scale value; inject the sample into a dry pycnometer, after constant temperature at the determination temperature record the liquid level scales on both arms and weigh, use the chart to find the apparent mass in air of an equal volume of water, and calculate the sample density in the same way as in 7.1.1.

4. Reagents and materials (purity / preparation)

4.1 U type vibrating tube method (Chapter 6)

• 6.3.1 Unless otherwise specified, only analytical grade reagents are permitted.
• 6.3.2 Washing solvent: any solvent may be used, as long as a clean and dry sample tube can be obtained.
• 6.3.3 Ammonium persulfate: prepare as a 8 g/L sulfuric acid solution. Warning: ammonium persulfate is a strong oxidant.
• 6.3.4 Calibration liquids: at least two calibration liquids are required to calibrate the sample tube; the density range of the selected calibration liquids should be within the density range of the test samples, and the density of the calibration liquids should be traceable to national standards or adopt internationally recognized values. When using water and air, they shall meet the requirements of 6.3.4.1 and 6.3.4.2.
• 6.3.4.1 Water: shall meet the grade two or higher requirements of GB/T 6682. Before use, filter with a 0.45 μm filter, boil to remove dissolved air and cool; once air has been removed, handle carefully to minimize re-dissolution of air. Water density values at different temperatures are given in Appendix A.
• 6.3.4.2 Air: the air density values used are given in Appendix B.
• 6.3.5 Water: for washing, shall meet the grade three requirements of GB/T 6682.

4.2 Pycnometer method (Chapter 7)

• 7.3.1 Anhydrous ethanol: analytical grade.
• 7.3.2 Petroleum ether: 30 °C～60 °C, analytical grade.
• 7.4.1 Chromic acid cleaning solution for cleaning (Note: strong acid and strong oxidant, handle with care when using); distilled water, anhydrous ethanol, dry air.

5. Instruments and equipment

5.1 Hydrometer method (5.3)

• 5.3.1 Hydrometer: made of glass, shall meet the technical requirements given in SH/T 0316 and Table 1.
• 5.3.2 Density cylinder: made of transparent glass, cylindrical, with a beveled spout on the upper edge; the inner diameter of the cylinder shall be at least 25 mm larger than the outer diameter of the hydrometer used; the height of the cylinder shall allow a distance of at least 25 mm between the bottom of the hydrometer when floating and the bottom of the cylinder.
• 5.3.3 Thermometer: shall meet the technical requirements of numbers GB-48 and GB-68 in GB/T 514; other fully immersed thermometers of suitable range with equal or higher precision may also be used.
• 5.3.4 Constant-temperature bath: the size shall be able to accommodate the density cylinder, so that the sample is completely immersed below the surface of the constant-temperature bath liquid, and the test temperature can be maintained within ±0.25 °C during the test.
• 5.3.5 Glass stirring rod: about 450 mm long.

Table 1 Technical requirements for hydrometers (excerpt from the source text):

(Note: In Table 1 of the source text, in the column "Scale interval per unit", the kg/m³ row SY-02 is 20, SY-05 is 50, SY-10 is 50; the g/cm³ row SY-02 is 0.02, SY-05 is 0.05, SY-10 is 0.05. Some values are suspected to have source-text extraction misalignment, requires confirmation against the source standard (source-text extraction).)

5.2 U type vibrating tube method (6.2)

• 6.2.1 Vibrating tube densimeter: calibrated, density resolution ±0.1 kg/m³ or higher.
• 6.2.2 Circulating constant-temperature bath: if a constant-temperature bath is required, it shall be able to maintain the temperature of the circulating liquid within ±0.05 °C of the required temperature.
• 6.2.3 Temperature sensor: calibrated, capable of measuring the sample tube temperature, accurate to at least ±0.10 °C; care should be taken to use a sensor with very thin wires to minimize heat transfer along the wires into and out of the sample tube.
• 6.2.4 Homogenizer: suitable for the sample and sample container, capable of homogenizing the sample; high-speed shears, static mixers, and other suitable forms may be used.

5.3 Pycnometer method (7.2)

• 7.2.1 Capillary-stoppered pycnometer: two models a and b (Figure 3).
  • 7.2.1.1 Guard-cap (ground-glass cap) type pycnometer (a in Figure 3): suitable for all samples except viscous and solid products, generally used for relatively volatile samples; the guard cap can reduce expansion and volatilization losses; it can be used for determining the density of liquid samples at temperatures below room temperature.
  • 7.2.1.2 Gay-Lussac pycnometer (b in Figure 3): suitable for non-volatile liquids except relatively viscous liquids.
• 7.2.2 Graduated double-capillary pycnometer (Figure 4): suitable for determining the density of highly volatile liquids; capacity 1 mL～10 mL; total mass not exceeding 30 g; specifications and dimensions are given in Table 6.
• 7.2.3 Constant-temperature water bath: water depth above 150 mm, temperature controllable at ±0.05 °C.
• 7.2.4 Bath thermometer: shall meet the technical requirements of GB/T 514; other fully immersed thermometers of suitable range with equal or higher precision may also be used.
• 7.2.5 Pycnometer holder: capable of supporting the pycnometer vertically so that it is located at a suitable position in the constant-temperature bath, made of corrosion-resistant metal or other materials; the graduated double-capillary pycnometer holder is shown in Figure 5.
• 7.2.6 Analytical balance: sensitivity 0.000 1 g.
• 7.2.7 Laboratory vacuum pump: 0.5 L/s～1 L/s.
• 7.2.8 Vacuum desiccator.

Table 6 Specifications and dimensions of the graduated double-capillary pycnometer (excerpt from the source text):

(Note: Table 6 source-text extraction is severely misaligned; most dimensions in the rows 1 mL, 2 mL, 10 mL could not be reliably matched in the source text and require confirmation against the source standard (source-text extraction).)

6. Recommended operating conditions

• Hydrometer method:
  • 5.2.2 Test temperature: heat the sample until it flows sufficiently, but the temperature must not be so high as to cause loss of light components; Note: determination of standard density is most accurate at the standard temperature 20 °C or close to 20 °C.
  • 5.3.4 Constant-temperature bath: maintain the test temperature within ±0.25 °C during the test.
  • 5.6.3 The change in ambient temperature shall not be greater than 2 °C; when greater than ±2 °C, a constant-temperature bath shall be used.
  • 5.6.12 If the temperature after the test differs from the temperature at the start of the test by more than 0.5 °C, the reading shall be taken again until the temperature change stabilizes within ±0.5 °C.
• U-type vibrating tube method:
  • 6.5.1.1 The sample density should be determined at the standard temperature whenever possible.
  • 6.5.1.2 If the sample tube itself has a thermostat, set the sample tube temperature to the required test temperature according to the manufacturer's instructions; otherwise, connect an additional constant-temperature bath to keep the temperature in equilibrium. The sample tube temperature and pressure of the density meter shall not exceed the manufacturer's specified operating range.
  • 6.2.2 The temperature of the circulating constant-temperature bath shall be maintained within ±0.05 °C.
  • 6.2.3 The temperature sensor shall be accurate to at least ±0.10 °C.
• Pycnometer method:
  • 7.4.2.2.1 The reference temperature for calibration of the pycnometer is 20 °C.
  • 7.4.2.2.2 Constant-temperature water bath 20 °C±0.05 °C, immersed to the middle of the pycnometer neck, with constant temperature for at least 1 h.
  • 7.4.2.3.1 Graduated double-capillary pycnometer: 20 °C±0.05 °C constant-temperature water bath, after constant temperature for 20 min, read the liquid level graduations on both arms.
  • 7.5.1.3 Capillary-stoppered pycnometer: constant temperature in a constant-temperature water bath for 20 min.
  • 7.5.2.3 Graduated double-capillary pycnometer: constant temperature in a constant-temperature water bath for 20 min.
  • 7.6.1 When used for product quality control, the reference temperature (such as 20 °C) is usually selected; when used for product quality or apparent quality calculations, the determination shall be made within ±3 °C of the product metering temperature; highly volatile samples shall be determined at 20 °C or below 20 °C.

7. Sampling and sample preparation

• Chapter 4 Sampling: sampling shall be carried out according to the method specified in the product standard; when there is no requirement in the product standard, samples shall be taken according to the provisions of GB/T 4756 and GB/T 6680.
• 5.2 Sample preparation for the hydrometer method:
  • 5.2.1 Mix the sample so as to minimize loss of light components and maintain sample integrity.
  • 5.2.1.1 Volatile petrochemical products: to reduce loss of light components, the sample shall be mixed in its original container and in a closed system. Note: mixing volatile samples in an open container will cause loss of light components and affect the measured density value.
  • 5.2.1.2 Residual petrochemical products: the sample shall be heated to the test temperature before mixing (see 5.2.2 and the note).
  • 5.2.2 Test temperature: heat the sample until it flows sufficiently, but the temperature must not be so high as to cause loss of light components.
• 6.4 U-type vibrating tube method sample preparation:
  • 6.4.1 General requirements: sample preparation shall minimize loss of light components. Note: when homogenizing or heating volatile petrochemical products containing sediment or water, loss of light components will inevitably occur, which may cause errors in the density determination.
  • 6.4.2 Petrochemical products that are free of water or sediment and have sufficient fluidity: mix by gently shaking.
  • 6.4.3 Petrochemical products containing water or sediment: mix the sample in the original container, taking all measures to minimize loss of light components.
  • 6.4.4 Residual petrochemical products: heat to a sufficiently fluid state before mixing.
• 7.5.2.5 Pycnometer method: for highly volatile samples containing large amounts of components with boiling points below 20 °C, or samples for which it cannot be certain whether loss occurs due to evaporation during the determination, cool the sample and the pycnometer to 0 °C～5 °C before filling; if the dew point is so high that water vapor condenses in the pycnometer, a drying tube may be attached to one arm of the pycnometer to prevent this; such samples shall be filled to the lower graduation line to minimize evaporation loss.

8. Analytical procedure

8.1 Hydrometer method (5.4～5.6)

• 5.4 Instrument verification:
  • 5.4.1 The hydrometer shall be periodically verified using a standard hydrometer traceable to national standards or the density of a traceable standard substance, and shall be re-verified at least every five years.
  • 5.4.2 The thermometer shall be periodically verified using a standard thermometer traceable to national standards.
• 5.5 Instrument preparation:
  • 5.5.1 Check the reference point of the hydrometer to determine whether the hydrometer graduations are in the correct position in the dry tube; if the graduations have shifted, this hydrometer shall be discarded.
  • 5.5.2 Bring the temperature of the hydrometer cylinder and hydrometer close to the sample temperature.
• 5.6 Test procedure:
  • 5.6.1 At the test temperature, transfer the sample to a clean hydrometer cylinder with a stable temperature, avoiding splashing of the sample and formation of air bubbles, and reducing volatilization of light components.
  • 5.6.2 Use a piece of clean filter paper to remove all bubbles formed on the surface of the sample.
  • 5.6.3 Place the cylinder containing the sample vertically in a place free of air movement; during the entire test, the change in ambient temperature shall not be greater than 2 °C; when greater than ±2 °C, a constant-temperature bath shall be used.
  • 5.6.4 Stir the sample with a suitable thermometer or stirring rod in a vertical rotating motion to make the density and temperature of the sample uniform throughout the cylinder; record the temperature to the nearest 0.1 °C; remove the thermometer or stirring rod from the cylinder.
  • 5.6.5 Place a suitable hydrometer into the liquid, release it when it reaches the equilibrium position, and let the hydrometer float freely, taking care to avoid wetting the dry tube above the liquid surface; push the hydrometer below the equilibrium point by 1 mm or 2 mm, and let it return to the equilibrium position, and observe the shape of the meniscus; if the shape of the meniscus changes, clean the dry tube of the hydrometer and repeat the operation until the shape of the meniscus remains unchanged.
  • 5.6.6 For opaque viscous liquids, wait for the hydrometer to slowly sink into the liquid.
  • 5.6.7 For transparent low-viscosity liquids, push the hydrometer into the liquid about two graduations, then release it; the portion of the dry tube above the liquid surface shall have as little residual liquid as possible.
  • 5.6.8 When releasing, gently rotate the hydrometer so that it can come to rest and float freely away from the cylinder wall; allow sufficient time for the hydrometer to come to rest and for all bubbles to rise to the surface, and remove all bubbles before reading.
  • 5.6.9 When the hydrometer floats freely away from the cylinder wall and is at rest, read the hydrometer graduation value according to 5.6.10 or 5.6.11, reading to the nearest 1/5 of the graduation interval.
  • 5.6.10 Determination of transparent liquids: first position the eye slightly below the liquid surface, then slowly raise it to the surface, first seeing an irregular ellipse, which then becomes a straight line tangent to the hydrometer graduations (see Figure 1); the hydrometer reading is the point at which the main liquid surface of the liquid is tangent to the hydrometer graduations.
  • 5.6.11 Determination of opaque liquids: position the eye slightly above the liquid surface for observation (see Figure 2); the hydrometer reading is the point at which the upper edge of the meniscus is tangent to the hydrometer graduations.
  • 5.6.12 After recording the hydrometer reading, immediately carefully remove the hydrometer and stir the sample vertically with a thermometer; record the temperature to the nearest 0.1 °C; if this temperature differs from the temperature at the start of the test by more than 0.5 °C, the hydrometer and thermometer readings shall be taken again until the temperature change stabilizes within ±0.5 °C; if a stable temperature cannot be obtained, place the hydrometer cylinder and its contents in a constant-temperature bath, and repeat the operation from 5.6.3.
  • 5.6.13 After use of a lead-shot wax-sealed hydrometer at temperatures above 38 °C, it shall be dried vertically and cooled.

8.2 U-type vibrating tube method (6.5～6.7)

• 6.5 Instrument preparation:
  • 6.5.1 Test temperature: see Section 6.
  • 6.5.2 Sample tube cleaning: clean and dry the sample tube with a washing solvent; if water is used, rinse with a washing solvent that is miscible with water, then blow dry with clean dry air. If organic deposits appear in the sample tube, inject ammonium persulfate solution into the sample tube for cleaning, remove the ammonium persulfate solution, rinse with water, then clean with a washing solvent miscible with water, and then blow dry with clean dry air.
• 6.6 Instrument calibration:
  • 6.6.1 The density meter shall be calibrated when first installed, when the test temperature changes, after repair, or after the system is disturbed; if more than 7 d has elapsed since the last calibration, it shall be recalibrated before use.
  • 6.6.2 If air is a calibration substance, fill the sample tube with ambient air, record the density reading or vibration period, and step 6.6.3 may be omitted.
  • 6.6.3 Inject the first calibration liquid (6.3.4) into the sample tube, allow it to reach temperature equilibrium with the sample tube, record the vibration period or density reading and the sample tube temperature, and clean and dry the sample tube according to 6.5.2.
  • 6.6.4 Inject the second calibration liquid into the sample tube, allow it to reach temperature equilibrium with the sample tube, and record the vibration period or density reading and the sample tube temperature.
  • 6.6.5 Calculate the sample tube constants according to the manufacturer's instructions.
  • 6.6.6 After calibration, clean and dry the sample tube according to the procedure given in 6.5.2.
• 6.7 Test procedure:
  • 6.7.1 When the sample tube is filled with ambient air, check the density meter reading and compare it with the standard value reached during calibration; it should be within its least significant digit ±1; if not, the sample tube should be cleaned and dried again and checked again; if the reading is still out of tolerance, the density meter should be recalibrated.
  • 6.7.2 Inject the sample into the sample tube with a suitable syringe or autosampler, filling the sample tube as required in the instructions.
  • 6.7.3 When using an autosampler, double injection or a check sample method should be used to check for errors caused by bubbles and to monitor system performance.
  • 6.7.4 At no stage may the sample be siphoned, because this can cause loss of light components; the sample should be poured into a syringe and then injected into the sample tube, or the sample should be forced into the instrument under pressure by an autosampler.
  • 6.7.5 When injecting the sample manually, turn on the sample tube illumination lamp before injection, and check whether there are bubbles in the sample tube while injecting as required by the manufacturer's instructions; if bubbles are found, empty the sample tube, inject again, and recheck for bubbles; after checking the sample tube, immediately turn off the illumination lamp, because the heat generated by the lamp affects the sample tube temperature.
  • 6.7.6 When the density reading displayed by the density meter stabilizes at 0.1 kg/m³ or the vibration period reaches five significant figures, record the displayed number and the sample tube temperature accurate to 0.1 °C. Note: If the vibration period or density reading keeps drifting, it indicates that the sample tube temperature has not yet reached equilibrium; random changes in the reading generally indicate the presence of air or bubbles in the sample tube, and the sample needs to be reinjected; if the reading changes due to bubbles, the test needs to be carried out at a lower temperature to ensure that the sample remains single-phase; if large water droplets are present in the sample before injection due to insufficient mixing, both the indicated density value and the vibration period will be unstable.
  • 6.7.7 When measuring the density of viscous liquids, a stable reading is sometimes obtained even when air or bubbles are present; for these liquids, the sample tube should be slightly pressurized and the density remeasured; if the liquid is single-phase, the density drift caused by pressurization will be very small; on the other hand, due to the presence of gas or air bubbles, a large drift in the density value will be observed when they are compressed; in this case, the sample should be reinjected.
  • 6.7.8 If the sample contains very fine suspended water droplets, observe the density immediately after thermal equilibrium is reached. Note: If the sample contains very fine suspended water droplets, and the sample remains in the sample tube for a long time, the water droplets will slowly coalesce and migrate to the lowest point of the sample tube, causing a significant change in density.
  • 6.7.9 Clean and dry the sample tube according to the procedure given in 6.5.2.

8.3 Pycnometer method (7.4～7.5)

• 7.4 Preparation:
  • 7.4.1 Pycnometer preparation: first remove contaminants from the pycnometer and stopper, thoroughly clean with chromic acid cleaning solution, rinse with water, then rinse separately with distilled water and anhydrous ethanol, and blow dry with dry air. Note: Chromic acid cleaning solution is a strong acid and strong oxidant, and care must be taken when using it.
  • 7.4.2 Pycnometer calibration—determination of the water value of the pycnometer:
    • 7.4.2.1 After drying the pycnometer, cool it to room temperature, eliminate possible static electricity, and weigh accurate to 0.000 1 g; this mass is the mass of the empty pycnometer (m₀). Note 1: If there is no static eliminator in the balance chamber, breathing on the pycnometer can be used to eliminate static electricity, but it must be ensured that the pycnometer has returned to constant mass before weighing; static elimination must be considered in all subsequent weighings. Note 2: All weighings must be carried out within a range not exceeding 5 °C to limit changes in air density and obtain maximum accuracy.
    • 7.4.2.2 Determination of the water value of a capillary-stoppered pycnometer:
      • 7.4.2.2.1 This standard specifies the reference temperature for calibrating the pycnometer as 20 °C.
      • 7.4.2.2.2 Fill the pycnometer with freshly boiled distilled water cooled to about 18 °C, insert the capillary stopper, and take care not to trap air bubbles; place the pycnometer in a constant-temperature water bath at 20 °C±0.05 °C, immerse it to the middle of the pycnometer neck, and keep it at constant temperature for at least 1 h; quickly wipe off excess water at the top of the capillary stopper with a piece of filter paper; if a guard-cap type pycnometer is used, firmly place the guard cap on the capillary stopper.
      • 7.4.2.2.3 Remove the pycnometer from the constant-temperature water bath and allow the pycnometer and its contents to cool to slightly below the constant-temperature water bath temperature; wipe the outer wall of the pycnometer dry with a clean, dry lint-free cloth, and weigh accurate to 0.000 1 g to obtain the mass of the pycnometer filled with water (m_c); the difference between this and the mass of the empty pycnometer (m₀) is the water value of the pycnometer.
      • 7.4.2.2.4 The water value of the pycnometer shall be determined at least five times, and its range shall not exceed 0.000 5 g; the arithmetic mean shall be taken as the water value of the pycnometer.
    • 7.4.2.3 Determination of the water value of a graduated double-capillary pycnometer:
      • 7.4.2.3.1 Inject freshly boiled distilled water cooled to about 18 °C into the pycnometer by siphon until the liquid level reaches above the scale line; place the pycnometer in a constant-temperature water bath at 20 °C±0.05 °C so that all the liquid in the pycnometer is immersed below the surface of the constant-temperature water bath; after maintaining constant temperature for 20 min, read the liquid level scales in the two arms, reading to the smallest division.
      • 7.4.2.3.2 Remove the pycnometer from the constant-temperature water bath, wipe it dry with a clean, dry lint-free cloth, and weigh accurate to 0.000 1 g.
      • 7.4.2.3.3 The difference between the apparent mass in air of the water-filled pycnometer and that of the empty pycnometer is the water value of the pycnometer; gradually remove a little water from the pycnometer and repeatedly determine a series of at least three water values at different upper, middle, and lower scale positions; plot the sum of the scale readings of the two arms against the corresponding water values to obtain a straight line, from which the water value of the pycnometer at any scale can be found; these points should lie on the straight line; if a point is more than two smallest divisions away from the straight line and remains unchanged after repeated determination, the pycnometer should be discarded.
    • 7.4.2.4 If the density at another temperature (t₀) needs to be determined, the water value of the pycnometer must be determined at the required temperature, and the operation method is the same as in 7.4.2.2 and 7.4.2.3.
    • 7.4.2.5 The pycnometer shall be calibrated once every two years.
• 7.5 Test procedure:
  • 7.5.1 Capillary-stoppered pycnometer method:
    • 7.5.1.1 Select a pycnometer of suitable type and size according to the sample; usually 25 mL and 50 mL are most suitable.
    • 7.5.1.2 Weigh the dry, clean pycnometer whose water value has been determined; for a pycnometer of 25 mL or larger capacity, accurate to 0.000 5 g; for a smaller-capacity pycnometer, accurate to 0.000 1 g.
    • 7.5.1.3 Fill the pycnometer with the sample, place it in a constant-temperature water bath, and immerse it to the middle of the pycnometer neck; keep the pycnometer at constant temperature in the constant-temperature water bath for 20 min so that it reaches the test temperature (t) and bubbles rise to the liquid surface; when the liquid level no longer changes, insert the capillary stopper that has been preheated to the test temperature, wipe off excess sample at the top of the capillary with filter paper so that the sample in the capillary forms a meniscus at the top of the stopper; if a guard-cap type pycnometer is used, put on the guard cap; if the liquid level still changes, keep it in the constant-temperature water bath until the liquid level stabilizes. Note: For product mixtures, it is necessary to ensure that the test temperature and the final reporting temperature are the same, unless an approximate result is acceptable and the volume composition of the mixture and the correction coefficients of the mixture components are known.
    • 7.5.1.4 Remove the pycnometer from the constant-temperature water bath; if it is not a guard-cap type pycnometer, cool it to slightly below the test temperature; if the test temperature is higher than room temperature, cool it to room temperature.
    • 7.5.1.5 Wipe off the water and sample on the outer wall of the pycnometer with a clean, dry lint-free cloth, then weigh to the accuracy specified in 7.5.1.2 to obtain the mass of the pycnometer containing the sample (m_s).
  • 7.5.2 Graduated double-capillary pycnometer method:
    • 7.5.2.1 Weigh the clean, dry pycnometer whose water value has been determined, accurate to 0.000 1 g.
    • 7.5.2.2 Fill the pycnometer by siphon with the sample at a temperature below the test temperature until the liquid level reaches the graduated part of the capillary (preferably reaching the middle or lower part of the scale).
    • 7.5.2.3 Place the pycnometer in a constant-temperature water bath, maintain constant temperature for 20 min, and read the liquid level scales in the two arms. Note: For product mixtures, it is necessary to ensure that the test temperature and the final reporting temperature are the same, unless an approximate result is acceptable and the volume composition of the mixture and the correction coefficients of the mixture components are known.
    • 7.5.2.4 Remove the pycnometer from the constant-temperature water bath, wipe it dry, cool it to room temperature, and then weigh, accurate to 0.000 1 g.
    • 7.5.2.5 For samples containing a large amount of highly volatile components with boiling points below 20 °C, or samples for which it cannot be certain whether loss occurs due to evaporation during the determination, cool the sample and pycnometer to 0 °C～5 °C before loading; if the dew point is quite high, causing water vapor to condense in the pycnometer, a drying tube may be attached to one arm of the pycnometer to prevent this phenomenon; for such samples, fill to the lower scale line to minimize evaporation loss; if the total length of the unfilled capillary arm exceeds 10 cm, the diffusion rate is very low, and even for a highly volatile compound such as isopentane, the evaporation loss during the determination is low enough to be negligible.

9. Qualitative and quantitative and calculation formulas

9.1 Density meter method (5.7)

• 5.7.1 After making the relevant corrections to the thermometer readings observed in 5.6.12, record to approximately 0.1 °C.
• 5.7.2 Since the hydrometer reading is calibrated according to the lower edge of the liquid meniscus, for opaque liquids, the observed hydrometer reading shall be corrected for the meniscus using the meniscus correction values given in Table 1.
• 5.7.3 After applying the relevant corrections to the observed hydrometer reading, record it to 0.1 kg/m³ (0.000 1 g/cm³).
• 5.7.4 The apparent density obtained in 5.7.3 is corrected for the expansion coefficient of the glass hydrometer using the following formula to obtain the density at the measurement temperature:
  • ρ_t = ρ'_t × [1 − 0.000 023(t − 20) − 0.000 000 02(t − 20)²] …… (1)
  • Where: t— temperature of the test sample, °C; ρ'_t— apparent density of the test sample at temperature t; ρ_t— density of the test sample at temperature t.
• 5.7.5 Use the following calculation formula to convert the density at the measurement temperature to the standard density at 20 °C; the density at other temperatures may also be calculated by the same algorithm:
  • ρ₂₀ = ρ_t + γ(t − 20) …… (2)
  • Where: γ— density-temperature coefficient, which can be obtained from tables or determined experimentally for different liquid chemical products. Note: This standard provides the γ values for some products in Annex C, which may be used for reference or determined experimentally for different liquid chemical products.

9.2 U type vibrating tube method (6.8)

• 6.8.1 If the density meter displays the vibration period, calculate the density of the sample from the observed vibration period of the sample tube according to the manufacturer's instructions.
• 6.8.2 The density at the standard temperature can be calculated using formula (2).

9.3 Pycnometer method (7.6)

• 7.6.1 When density is measured for product quality control, the measurement temperature is usually the reference temperature (e.g., 20 °C); when density is measured for product quality or apparent quality calculation, it should be measured within ±3 °C of the product metering temperature; however, for highly volatile samples, to reduce loss of light components, density should be measured at or below 20 °C or 20 °C.
• 7.6.2 Density calculation:
  • 7.6.2.1.1 When t = t₀, calculate the density of the test sample ρ_t (kg/m³) according to formula (3):
    • ρ_t = [(m_s − m₀) / (m_c − m₀)] × (ρ_c − C) + C …… (3)
    • Where: t₀—temperature at which the pycnometer was calibrated with water (reference temperature 20 °C), in degrees Celsius (°C); m₀—apparent mass of the empty pycnometer in air, in grams (g); m_c— at calibration temperature t₀, the apparent mass of the pycnometer filled with water in air, in grams (g); m_s— at measurement temperature t, the apparent mass of the pycnometer filled with liquid test sample in air, in grams (g); C— air buoyancy correction value, in kilograms per cubic meter (kg/m³) (see Table 7 and Note 2); ρ_c— density of water at calibration temperature t₀, in kilograms per cubic meter (kg/m³) (see Annex A); ρ_t— density of the test sample at the measurement temperature, in kilograms per cubic meter (kg/m³).
  • 7.6.2.1.2 When t ≠ t₀, calculate the density of the test sample ρ_t (kg/m³) according to formula (4):
    • ρ_t = [(m_s − m₀) / (m_c − m₀)] × (ρ_c − C) + C − α(t₀ − t) …… (4)
    • Where: t— measurement test