ISO 975:2021 pdf download – Brown coals and lignites — Determination of yield of benzene-soluble extract — Semi-automatic method.
8.3 Procedure Transfer a mass of about 2 g (determined to the nearest 0,1 mg) of general analysis test sample to the extraction thimble (6.2) and cover with a pad of absorbent cotton, which is fitted snugly on the wall of the thimble. Place the extraction thimble with sample in the extraction chamber (6.1). Add 60 ml to 70 ml of benzene to a previously dried flask of known mass (determined to the nearest 0,1 mg). Assemble the instrument. Switch on the electrical power. Push down the programme button. The instrument will automatically perform the experiment in accordance with the following sequence: — The extraction-evaporation device is lowered until the flask is immersed in the water bath as in the preliminary adjustment and the condenser is in an inclined position permitting refluxing. The heating of the water bath is started simultaneously. — When the extraction temperature previously set is reached, the pump begins to circulate the hot water between the bath and the jacket of the extraction chamber. The benzene vapour from the flask passes through the extraction chamber and reaches the condenser, where it is condensed and drips onto the thimble. The extraction stage is thus in progress. — After 180 min, or an otherwise set time, the pump stops and extraction is finished. Hot water flows back to the bath. The temperature of the extraction chamber drops to a temperature at which the benzene vapour can only reach the extraction chamber and condenses there. Thus a rinsing action is achieved, by means of which the benzene-soluble extract adhered to the wall is washed down into the flask by the condensed benzene. This is the rinsing stage. — After 10 min, rinsing is finished. The condenser is automatically changed to an inverted position permitting distillation. The pump works again so as to resume hot-water circulation. The benzene vapour condenses in the condenser and flows to the receiver. The stage of evaporation starts.