BS ISO 334:2020 pdf download – Coal and coke — Determination of total sulfur — Eschka method
8.3 Ignition
8.3.1 For coal Place the charged crucible (and any others up to the limit of the muffle furnace capacity) in the cold muffle furnace (6.3) and raise the temperature to 800 °C ± 25 °C in about 1 h, maintaining this temperature for at least a further 1,5 h. Withdraw the crucible (or crucibles) and allow to cool. NOTE The cracking of porcelain crucibles can be prevented if they are slowly cooled by insertion in supports of light porous firebrick on removal from the muffle furnace.
8.3.2 For coke Place the charged crucible (or crucibles) on the cold insulating flat plate (6.5) and insert into the muffle furnace (6.3) at a temperature of 800 °C ± 25 °C, maintaining this temperature for at least a further 1,5 h. Withdraw the crucible (or crucibles) and allow to cool. See Note in 8.3.1.
8.4 Recovering the residue Transfer the ignited mixture from the crucible to a 400 ml beaker containing 25 ml to 30 ml of water. If unburnt particles are present, the determination shall be stopped and the test repeated. Wash the crucible thoroughly with about 50 ml of hot water and add the washings to the contents of the beaker.
8.5 Extraction Place a watch glass on the beaker and then, while tilting the watch glass, carefully add enough hydrochloric acid (5.2) to dissolve the solid matter (17 ml will normally be required), warming the contents of the beaker to effect solution. Boil for 5 min to expel carbon dioxide and filter, collecting the filtrate in a 400 ml conical beaker.
NOTE A medium-textured, doubly acid-washed filter paper or a filter-paper pad is recommended for speed of filtration. To prepare the filter-paper pad, shake doubly acid-washed filter-paper clippings, in pieces with areas of approximately 1 cm 2 , with water in a bottle until the paper is thoroughly disintegrated. Place a porcelain filter cone of 25 mm in a 75 mm funnel, close the stem of the funnel with a finger, and add water until the cone is immersed and the funnel stem is full. Shake, onto the cone, sufficient paper pulp to form a pad 5 mm thick, and level it with a flat-ended glass rod. Allow the excess water to drain away by removing the finger from the stem and as drainage ceases, lightly tamp the pad around the edges with the glass rod. A final wash with water renders the filter ready for use. Wash the filter with five 20 ml portions of hot water. Add two or three drops of the methyl red indicator solution (5.5) to the combined filtrate and washings, and then cautiously add the ammonia solution (5.6) until the colour of the indicator changes and a trace of precipitate is formed. Add enough hydrochloric acid (5.2) to just redissolve the precipitate and then add 1 ml in excess.
8.6 Precipitation of barium sulfate
After extraction, dilute the solution, if necessary, to approximately 200 ml and cover the beaker containing the solution with a watch glass. Heat the covered beaker until the solution boils and then reduce the heating slightly until ebullition of the solution ceases. Then add 10 ml of the cold barium chloride solution (5.4) from a pipette with a delivery time of approximately 20 s so that the barium chloride solution falls into the centre of the hot solution while it is being agitated. Keep the solution just below boiling point for 30 min.
Filter the solution using one of the following techniques.
a) By gravity through an ashless, close-textured, doubly acid-washed filter paper of diameter 100 mm to 125 mm. Carefully fold the filter paper and fit it into a fluted, long-stemmed 60° funnel so that the stem remains full of liquid during the filtration.
b) By gravity through a filter-paper pad prepared from ashless, doubly acid-washed filter paper (see Note in 8.5).
c) By suction through a pad of filtration mineral fibre in a Gooch crucible (6.6). Before commencing the filtration, dry the Gooch crucible and pad for 1 h at a temperature of 130 °C ± 10 °C and weigh, to the nearest 0,1 mg. Wash the precipitate with hot water, using not more than 250 ml, until the last 20 ml of the washings give not more than a faint opalescence with the silver nitrate solution (5.7). If techniquea) or b) is used, place the wet filter paper or pad in the previously ignited and weighed crucible (6.4) on the cold flat plate (6.5).
If technique b) is used, after transferring the filter-paper pad to the crucible, wipe the funnel successively with two halves of an ashless filter paper and place this paper in the crucible with the pad. Insert the crucible slowly into the muffle furnace (6.3), at a temperature of 800 °C ± 25 °C, and then heat for 15 min. Cool in a desiccator and reweigh, to the nearest 0,1 mg. If technique c) is used, dry the Gooch crucible (6.6) and pad for 1 h at a temperature of 130 °C ± 10 °C, cool in a desiccator, and reweigh, to the nearest 0,1 mg.