a few with a larger quantity of that fluid. The upper edge of the
filter-paper is specially liable to escape complete washing. Excessive
washing must be avoided; the point at which the washing is complete is
found by collecting a little of the filtrate and testing it. The
precipitate is removed from the filter-paper for further treatment by
opening out the paper and by washing the precipitate with a jet of water
from a wash-bottle into a beaker, or back through the funnel into the
flask. In some cases, when the precipitate has to be dissolved in
anything in which it is readily soluble, solution is effected in the
filter itself allowing the liquid to run through as it is formed.

~Drying and Igniting.~--Precipitates, as a rule, require drying before
being ignited. With small precipitates the filter-paper may be opened
out, and placed on a warm asbestos slab till dry; or the funnel and the
filter with the precipitate is placed in a warm place, and supported by
any convenient means. The heat must never be sufficient to char the
paper. Some precipitates must be dried at a temperature not higher than
100∞ C. These are placed in the water-oven (fig. 20), and, when
apparently dry, they are taken from the funnel, placed between glasses,
and then left in the oven till they cease to lose weight. Such
precipitates are collected on tared filters. Those precipitates which
will stand a higher temperature are dried in the hot-air oven at a
temperature of from 120∞ to 150∞. The drying is continued until they
appear to be free from moisture, and until the precipitate ceases to
adhere to the filter. In drying sulphides the heat must not be raised to
the melting point of sulphur, since, if there is any free sulphur
present, it fuses and filters through.

[Illustration: FIG. 20.]