COEI-2-CENDRE Sulphuric cinders

The sulphuric cinders result from the calcination after being in contact with air after being attacked by sulphuric acid.

Heat a silica or platinum crucible of low form for 30 min until red; allow to cool in a vacuum dessicator and tare the crucible. Place the exactly weighed test sample in the crucible and wet it with a sufficient quantity of concentrated sulphuric acid (R) diluted beforehand by an equal volume of water. Heat until dry evaporation, then in a muffle oven, first carefully until red without exceeding the temperature of 600°C 25°C. Maintain calcination until the black particles disappear, allow to cool, add 5 drops of sulphuric acid diluted to half to the residue, then evaporate and calcinate as previously until constant weight; weigh after cooling in the desiccator.

Calculate the rate of sulphuric cinders referring to 100 g of substance.

Total cinders

The total cinders result from the calcination of the product after contact with air.

Heat a silica or platinum crucible of low form for 30 min until red. Allow to cool in a vacuum dessicator and tare the crucible. Dispose homogenously the exactly weighed test sample in the crucible. Desiccate for an hour in the incubator at 100°C-105°C. Incinerate in the muffle oven, first carefully to avoid that the sample catches fire, then until red at a temperature of 600°C  25°C. Maintain the calcination until the black particles disappear. For 30 min allow to cool in a vacuum desiccator. Weigh. Continue the calcination until constant mass.

If the black particles persist, take up the cinders in hot distilled water. Filter these cinders on an ashless filter paper (porosity 10 µm). Incinerate the filter and residue until constant mass. Group the new cinders with the filtrate. Evaporate the water. Incinerate the residue until constant mass.

Calculate the rate of total cinders by referring to 100 g of substance.