Scientific American Supplement, No. 455, September 20, 1884 | Page 7

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.
The sample for examination is moistened with water and mixed with an
adequate volume of the solvent, is digested at 50-60° C. until complete
decomposition is effected. The heating of the liquid prevents the
solution of iron, manganese, and cadmium. The content, sediment and
liquid, is thrown on a filter and washed with hot water to which a small
quantity of the solvent has been added. When the solution contains iron
and manganese, it is separated by decantation from the sediment and
oxidized with bromine (according to the method of Nic-Wolff) until a
flocculent precipitate of iron sesquioxide and manganese dioxide
becomes visible; it is united with the original residue and filtered.
The filtrate is diluted till it appears cloudy, boiled to expel ammonia,
tested with sodium sulphide upon the presence of zinc, and, when freed

of all zinc, decanted. The precipitate of zinc carbonate is filtered,
exhausted with water, transferred into zinc oxide by ignition, and
weighed. The gravimetric method can be substituted by the volumetric
by introducing a solution of sodium sulphide of known strength into the
ammoniacal filtrate. On dividing the filtered liquid into various equal
portions other substances, arsenic and sulphuric acid, can be
determined from the same sample. For this purpose the filtrate is
concentrated; divided into two equal portions, one of which is acidified
and treated with hydrogen sulphide for the determination of arsenic,
the other is acidified and used for the estimation of sulphuric acid by
means of barium chloride. The original residue is dissolved in muriatic
or acetic acid and filtered. The lead of the filtered liquid is thrown
down by sulphuric acid, and alcohol, and cadmium, after dissipation of
alcohol into gas, precipitated by hydrogen sulphide. Iron, manganese,
alumina, and other substances present in the solution are determined
by known methods.
It is manifest that the determination of substances--zinc, lead, and
sulphuric acid--which are of importance in technical analysis of zinc
ash, can be executed by this method within a comparatively short time.
The application of ammonium carbonate as solvent has the advantage,
over the application of ammonia, that it is a far better solvent, that it
decomposes insoluble basic sulphates, and that the remaining
carbonates are readily dissolved by acids.
The decomposition of zinc dust is accompanied by a lively evolution of
gas; it is therefore necessary to continue the digestion of the sample till
no more hydrogen is given off. Zinc dust contains both metals and their
oxides, and methods which, from the volume of hydrogen generated,
determine indirectly the percentage of