Definitions.—Ignition is the heating of a substance to a high temperature.
Fusion is the heating of a substance to the melting-point.
Intumescence is the swelling of the substance upon heating.
Decrepitation is the crackling of a substance due to the sudden expansion of combined water upon heating.
Deflagration is the burning of a substance with explosive violence, generally due to excess of oxygen.
Incandescence is the white light emitted by a substance that is infusible when subjected to a high temperature.
Examination on Charcoal alone.—The size of the assay should be about that of a mustard seed. This is sufficiently large to show all of the reactions clearly, and though a larger piece would exhibit the characteristic phenomena, yet much more effort is required. A very small, shallow hole should be cut in the Ch. to receive the assay. The Bp. flame should be directed at an angle of about 30° with the surface of the Ch. Considerable care must be taken lest the hole in the Ch. is burned too deep and the assay lost in the coal.
The force of the air from the jet must also be borne in mind for a strong blast, or sudden puffs may blow the substance away.
The following changes are to be looked for:—
a. Whether the substance is volatile or non-volatile.