11. Preparation of Specimen and Filling Test Cell
11.1 Store the sample in its original sealed container, shielded from light. Some liquids, such as oils of petroleum origin, undergo changes when exposed to sunlight. Allow the sealed container to stand undisturbed in the room in which the test is to be made for a sufficient period of time to permit the sample to attain room temperature before it is opened.
11.2 When insulating liquids are heated to elevated temperatures, some of their characteristics undergo a change with time and the change, even though of the minutest nature, may be reflected in the loss measurement. It is therefore desirable that the elapsed time necessary for the test specimen to attain temperature equilibrium with the test cell be held to a minimum. For optimum procedure do not exceed 20 min for this time. It is essential, therefore, that the procedures outlined below be closely followed.
11.3 Forced - Draft Oven:
11.3.1 In order that representative test specimens may be obtained, gently tilt or invert the sample container and swirl the liquid several times. Immediately after mixing the sample, pour a quantity of liquid sufficient for four fillings of the test cell into a chemically clean dry beaker and heat on a hot plate to a temperature 2°C below the desired test temperature. Stir the fluid frequently during heating.
11.3.2 Remove the cell from the test chamber, lift out the inner electrode, but do not rest it on any surface, and fill the cell with a portion of the heated specimen. Replace the beaker with the remainder of the heated sample on the hot plate. Insert the inner electrode and rinse the electrodes by twice raising and lowering the inner electrode. Remove the inner electrode and hold it suspended in air; then decant the rinsing liquid and immediately fill the cell from the remainder of the heated specimen. Replace the inner electrode.
11.3.3 Insert a mercury thermometer graduated in 0.25°C increments, or other temperature measuring devices (for example, thermocouples) that provide equal accuracy, in the
thermometer well provided in the inner electrode (Warning - A spring-loaded thermocouple may be used for measuring the temperature of the inner electrode, but extreme caution shall be exercised that these wires do not come in
contact with the high-voltage lead and do not pick up stray emfs). Immediately return the filled cell to the test chamber (adjusted to a temperature above the desired test temperature)
and make the necessary electrical connections to the cell.
11.3.4 Perform the operations described in 11.3.2 and 11.3.3 as rapidly as possible.
11.4 Automatic Thermo - Regulator Cell:
11.4.1 Gently swirl or invert the sample container to obtain a representative test specimen.
11.4.2 Fill the test cell and flush to rinse thoroughly both the inner and outer electrodes with a portion of the sample. Decant the rinsing liquid and immediately fill the cell with a new aliquot of sample.
11.4.3 Replace inner electrode and make all necessary electrical connections to the cell. On some instruments the cell must be in place before filling with specimen.
11.4.4 Set the automatic thermo-regulator for the test temperature and initiate heating. Record data as soon as the test temperature is reached.
