2. Flue dust, condensed in chambers of zinc furnaces with Kleemann's
receivers,

3. Zinc ash, of various assortments, from iron blast furnaces.

Of these, zinc dust is the only ready product which is, as color or
reducing agent, employed in analytical and technical processes. Its value,
when serving the latter purpose, is determined by the percentage of finely
divided metallic zinc and cadmium contained therein; of equal reducing
power is cadmium, generally associating zinc; injurious, and therefore
uneffective, are zinc oxide and oxides of other metals, also metallic
lead.

Flue dust, condensed in chambers of zinc furnaces with Kleemann's
receivers, is employed with zinc ores in the extraction of zinc, and in
small quantities as substitute for zinc white; its commercial value is
similarly estimated as that of zinc ores.

The various modifications of zinciferous flue ashes from blast furnaces
are an object for continual demand, being both a valuable material for the
production of zinc and, in its superior qualities, a desirable pigment. In
the regeneration of zinc the presence of foreign substances is of some
concern; detrimental are lead, sulphur, and sulphuric acid in form of
lead, zinc, and lime sulphate.

The chemico-technical analysis of these products has until recently been
confined to the volumetric determination of zinc by means of sodium
sulphide (Schaffner's method). But as a remnant of sulphur, as sulphuric
acid, in roasted blende causes a material loss during distillation, and