Carbonise by setting light to the substance with a strip of ash-free filter paper.

Filter while warm through an ash-free filter and wash the filter in 50 ml of warm water (see observation 7).

Filter on ash-free filter paper and collect the filtrate in a 250 ml volumetric flask.

Filter the warm solution through an ash-free filter paper and wash the residue with warm water until the acid reaction is no longer visible.