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 otherwise being induced to produce a zinc free of lead, the estimation of sulphur, sulphuric acid, and lead became necessary.  These impurities are determined by well-known methods; sulphur is oxidized and precipitated with barium chloride, lead by sulphuric acid and alcohol.  The examination of zinc dust, when used for the regeneration of metal, determines the quantity of zinc resident therein, and employed as reducing agent, the quantity of metal which causes the generation of hydrogen.  Cadmium, showing the same deportment, must also be considered as well as lead and arsenic.

A most complete and rapidly working method for the examination of zinciferous products has originated with the application of neutral ammonium carbonate as solvent.  A solution of this preparation is made, according to H. Rose, by dissolving 230 grm. commercial ammon carbonate in 180 c.c. ammoniacal liquor of 0.92 s.g., and, by addition of water, augmenting it to one liter.

This solution dissolves the metallic components, their oxides, and basic zinc sulphate, and transfers cadmium and lead oxide, also lead, magnesium, and lime sulphate, into insoluble carbonates.  Iron and manganese, when present as protoxide, are dissolved; of iron sesquioxide but traces, and of cadmium oxide in statu nascendi a small portion enter into solution.  The solution of ammonium carbonate contains in each 10 c.c. 1 grm. ammonia, which dissolves 1.5 grm. zinc.