ASTM D1837 Standard Test Method for Volatility of Liquefied Petroleum (LP) Gases
6. Procedure
6.1 Positioning the Thermometer - Add water to the 5 mL line of the weathering tube. Add two grains of charcoal. Insert the armored thermometer as low as possible into the weathering tube. Observe and record the water level in the tube. Remove and discard the water and charcoal and clean and dry the weathering tube.
6.2 Obtaining a Test Portion:
6.2.1 Fill the cooling vessel with the precoolant so as to cover the cooling coil.
6.2.2 The source of the sample (test portion) may be a process or delivery line, or a sample cylinder, taking care to obtain a liquid sample.
6.2.3 Attach the inlet of the cooling coil to the source from which the sample is to be taken with a short line connection of 6.4 mm (1/4 in.) pipe (or larger), having a sampling valve large enough to prevent vaporization of the material due to the drop in pressure across the valve seat.
6.2.4 Purge the sampling line and cooling coil by opening both the sampling valve and the 3.2 mm (1/8 in.) needle valve on the downstream end of the cooling coil.
6.2.5 Fill the weathering tube with the sample flowing through the cooling coil.
6.2.6 Empty this first sample.
6.2.7 Add two grains of similar-sized charcoal as was used in 6.1, and then refill the weathering tube to the 100-mL mark with fresh liquid sample passing through the cooling coil.
6.3 Placement of Thermometer - Carefully insert the precooled armored thermometer into the centrifuge tube, to the same position as in 6.1, and center it in the tube by means of a slotted cork. Take all 5 % residue readings at the level established in 6.1.
NOTE 3 - Inadequate precooling of the sample will result in excessive vaporization and loss of light components from the sample collected in the weathering tube. This results in proportionally more of the higher boiling components in the sample in order to collect 100 mL of liquid. As a result, the test is made more severe, with a higher reported 95 % evaporation temperature, which is on the conservative side.
6.4 Weathering Butane and Propane-Butane Mixture Types of Liquefied Petroleum Gas Products - When the temperature of the sample is below -12°C (10°F), allow it to weather in the atmosphere until the temperature has reached -12°C (10°F). At this point, place the weathering tube, with the armored thermometer still in place, in the water bath in a vertical position, submerging it to the 1 1/2 -mL mark, and allow the contents to weather.
6.5 Weathering Propane Type of Liquefied Petroleum Gas Products - Allow the sample to weather in the atmosphere, taking care to disturb the frost on the tube as little as possible. An acetone or alcohol swab can be used to remove frost sufficient to permit reading of the temperature.
6.6 Reading of Temperature - When the liquid level in the weathering tube, with the armored thermometer still in place, corresponds to the level previously determined in 6.1, read and record the temperature of the sample in accordance with 6.4 and 6.5.
6.7 Temperature Correction - Following the final temperature reading (6.6), remove the armored thermometer from the weathering tube and place it in a bath of finely crushed ice up to the immersion point. Observe the reading of the thermometer when a constant reading is obtained. If the thermometer reading is less than 0°C (32°F), add the fraction of a degree it is low to the final test reading. If the thermometer reading is more than 0° (32°F), subtract the fraction of a degree that it is high from the final test reading. If the thermometer reading varies more than 0.5°C (1°F), the test result is invalid. Repeat the procedure using an accurate thermometer.
NOTE 4 - A high reading of the thermometer when it is placed in ice usually indicates that there is a break in the mercury-thallium thread. This can be corrected by warming the thermometer gently in a warm water bath to drive the break upward into the expansion chamber at the top of the thermometer. While the mercury-thallium is continuous in the upper chamber, tap the bottom of the thermometer on a hard, but cushioned surface, to join the liquid into a continuous thread. A low reading in ice usually indicates that some of the liquid has remained in the expansion chamber. To correct this, allow the thermometer to warm so the liquid enters the chamber and tap as previously instructed
