In order to examine a substance before the blowpipe to determine the presence or absence of certain elements, it becomes necessary to arrange a systematic method. As with all branches of chemical work, one's success is largely dependent upon neatness of manipulation and carefulness of observation. The following order of observation is essentially that given by Berzelius:-- 1. Examination on charcoal by itself. 2. Examination on charcoal with Na_{2}CO_{3}. 3. Examination in ignition tube with Na_{2}CO_{3} and charcoal. 4. Examination on platinum wire. 5. Examination in borax bead. 6. Examination with Co(NO_{3})_{2}. After having examined a body in these six different ways, we shall be able to say what are its principal constituents. Before describing the method of carrying out these six different operations, it will be necessary to give a few definitions of terms which we shall have frequent occasion to employ. ~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. _Illustrations._ Examine before the Bp. on Ch. some arsenious oxide, As_{2}O_{3}, also some alumina, Al_{2}O_{3}. _b._ Whether the substance is fusible or infusible. _Illustrations._ Examine before the Bp. on Ch. some silver oxide, AgO, also some zinc oxide, ZnO. _c._ Whether the substance is alkaline or non-alkaline when placed upon moistened red litmus. _Illustrations._ Ignite some calcium carbonate, CaCO_{3}, before the Bp. on Ch., and place residue on moistened red litmus. In like manner, examine some magnesium carbonate, MgCO_{3}. _d._ Color of coating on Ch. caused by combination of metal and oxygen due to heat of Bp. flame.