ntioned as
required.

CHAPTER II

GENERAL OUTLINE OF BLOWPIPE ANALYSIS

[ABBREVIATIONS: O. F. for oxidizing flame, R. F. for
reducing flame, Ch. for charcoal, Ct. for coating, Bp. for
blowpipe.]

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 deg. 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