The precipitate, having been dried, is transferred to a watch-glass. The
filter-paper is opened out over a sheet of note-paper, and, with a
camel-hair brush, the precipitate is gently brought into the glass. Most
precipitates come away easily, and the transfer can be made without
apparent loss. The watch-glass is covered by the funnel, and the
filter-paper (folded into a quadrant) held by the tweezers and set fire
to with the flame of a Bunsen burner. It is allowed to burn over the
crucible, into which the black bulky ash is allowed to drop, and two or
three drops of nitric acid are then added. The crucible is placed on a
pipe-stem triangle (fig. 21), supported on a tripod. It is at first
heated gently with a Bunsen burner, and afterwards more strongly, until
the residue is free from carbon. It is cooled, and treated with any acid
necessary to convert the small amount of precipitate into the state in
which it is to be weighed; heated again, and cooled. The main
precipitate is transferred to the crucible, and the heating repeated
very gently at first, but more strongly towards the end of the
operation. It is next placed in the muffle, and, after two or three
minutes at a red heat, it is removed and allowed to cool in the
desiccator before weighing. This is for bodies that will bear a red
heat; for those compounds that require a lower temperature the heating
in the muffle is omitted. The muffle used for this purpose must not be
used at the same time for cupelling; a gas muffle (fig. 22), such as one
of Fletcher's, is best. A desiccator (fig. 23) is an air-tight vessel
which prevents access of moisture, &c., to the substance. Usually the
air in it is kept dry by means of a basin containing sulphuric acid.

[Illustration: FIG. 21.]

[Illustration: FIG. 22.]