The sample for examination is moistened with water and mixed with an adequate volume of the solvent, is digested at 50-60 deg.  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 metallic zinc do not give the real composition of the zinc dust.  For the determination of the metallic components the material is digested with a solution of copper sulphate, which dissolves zinc and cadmium; the liquid is filtered, acidified, and decomposed with hydrogen sulphide, or treated