ASTM D1298 for density of crude petroleum and liquid petroleum products
ASTM D1298 for density of crude petroleum and liquid petroleum products by hydrometer method
10. Procedure
10.1 Bring the hydrometer cylinder and thermometer to within approximately 5°C of the test temperature.
10.2 Transfer the sample to the clean, temperature-stabilized hydrometer cylinder without splashing, to avoid the formation of air bubbles, and minimize evaporation of the lower boiling constituents of more volatile samples. (Warning - Extremely flammable. Vapors may cause flash fire!)
10.3 Transfer highly volatile samples by siphoning or water displacement. (Warning - Siphoning by mouth could result in ingestion of sample!)
10.3.1 Samples containing alcohol or other water-soluble materials should be placed into the cylinder by siphoning.
10.4 Remove any air bubbles formed after they have collected on the surface of the test portion, by touching them with a piece of clean filter paper before inserting the hydrometer.
10.5 Place the cylinder containing the test portion in a vertical position in a location free from air currents and where the temperature of the surrounding medium does not change more than 2°C during the time taken to complete the test. When the temperature of the test portion differs by more than 2°C from ambient, use a constant temperature bath to maintain an even temperature throughout the test duration.
10.6 Insert the appropriate thermometer or temperature measurement device and stir the test portion with a stirring rod, using a combination of vertical and rotational motions to ensure uniform temperature and density throughout the hydrometer cylinder. Record the temperature of the sample to the nearest 0.1°C and remove the thermometer/temperature measuring device and stirring rod from the hydrometer cylinder.
NOTE 6 - If a liquid-in-glass thermometer is used, this is commonly used as the stirring rod.
10.7 Lower the appropriate hydrometer into the liquid and release when in a position of equilibrium, taking care to avoid wetting the stem above the level at which it floats freely. For low viscosity transparent or translucent liquids observe the meniscus shape when the hydrometer is pressed below the point of equilibrium about 1 to 2 mm and allowed to return to equilibrium. If the meniscus changes, clean the hydrometer stem and repeat until the meniscus shape remains constant.
10.8 For opaque viscous liquids, allow the hydrometer to settle slowly into the liquid.
10.9 For low viscosity transparent or translucent liquids depress the hydrometer about two scale divisions into the liquid, and then release it, imparting a slight spin to the hydrometer on release to assist in bringing it to rest floating freely from the walls of the hydrometer cylinder. Ensure that the remainder of the hydrometer stem, which is above the liquid level, is not wetted as liquid on the stem affects the reading obtained.
10.10 Allow sufficient time for the hydrometer to come to rest, and for all air bubbles to come to the surface. Remove any air bubbles before taking a reading (see 10.4).
10.11 If the hydrometer cylinder is made of plastic, dissipate any static charges by wiping the outside with a damp cloth. (Warning - Static charges often build up on plastic cylinders and may prevent the hydrometer from floating freely.)
10.12 When the hydrometer has come to rest floating freely away from the walls of the cylinder, read the hydrometer scale reading to the nearest one-fifth of a full scale division in accordance with 10.12.1 or 10.12.2.
10.12.1 For transparent liquids, record the hydrometer reading as the point on the hydrometer scale at which the principal surface of the liquid cuts the scale by placing the eye slightly below the level of the liquid and slowly raising it until the surface, first seen as a distorted ellipse, appears to become a straight line cutting the hydrometer scale (see Fig. 1).
10.12.2 For opaque liquids record the hydrometer reading at the point on the hydrometer scale to which the sample rises, by observing with the eye slightly above the plane of the surface of the liquid (see Fig. 2).
NOTE 7 - When testing opaque liquids using a metal hydrometer cylinder, accurate readings of the hydrometer scale can only be ensured if the liquid surface is within 5 mm of the top of the cylinder.
10.13 Immediately after recording the hydrometer scale reading, carefully lift the hydrometer out of the liquid, insert the thermometer or temperature measurement device and stir the test portion vertically with the stirring rod. Record the temperature of the test portion to the nearest 0.1°C. If this temperature differs from the previous reading (10.6) by more than 0.5°C, repeat the hydrometer observations and thermometer observations until the temperature becomes stable within 0.5°C. If a stable temperature cannot be obtained, place the hydrometer cylinder in a constant temperature bath and repeat the procedure from 10.5.
10.14 If the test temperature is higher than 38°C, allow all hydrometers of the lead shot-in-wax type to drain and cool in a vertical position.
