Charcoal, general characteristics

Detection.—Sulphur in the free state is readily recognisable by its general appearance and characteristics, and especially by its combustion to sulphur dioxide. Both in mixtures and compounds the presence of the element can be demonstrated by heating with charcoal and an alkali carbonate,2 or even better, on a small scale, by heating with an equal bulk of sodium or potassium,3 or with powdered iron 4 in each case some of the sulphur is converted into sulphide, which may be detected by the action of an aqueous extract on mercury or silver, or on sodium nitroprusside the metals are blackened, whilst the nitro-prusside is very sensitive in giving a purple coloration (see p. 62). Alternatively, the solution of the alkali sulphide may be acidified and tests applied for hydrogen sulphide to the vapours evolved on warming. 

Pine charcoal burns in combination with ammonium perchlorate at F/O = 2 10 producing a yellow flame, but no sparks or fire dust. A mixture of pine charcoal, sulphur and potassium nitrate in the weight ratio 30 10 60 burns producing pretty. orange red fire dust. This characteristic is generally seen with other charcoals but pine charcoal produces the most pretty fire dust of all. On the other hand, the phenomenon shows that pine charcoal does not complete the reaction and produces less gas in black powder-type compositions. Therefore pine charcoal is used to produce fire dust and not to obtain force. 

The microscopic structure of plant materials is for the most part preserved in the pyrolysis process. Characteristic damage to the fine structures and this general preservation of micro structure allow even finely powdered charcoals to be identified. 

The adsorbents that have been used are numerous and varied in nature They include charcoal, cellulose. Fuller s earth, silica gel, and alumina. The choice of adsorbent is based on the polarity and characteristics of the compounds to be separated, but in most instances an appropriate grade of activated alumina gives excellent results. In general, the polarity of the adsorbent should be significantly less than that of the substances to be separated. 

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