Colloidal solution, sulfuric acid preparation

Sulfur forms three binary compounds with indium, In2S, InS, and In2S3. The latter is prepared by direct union of the elements, by heating ln208 with sulfur or H2S or by passing H2S into the weakly acid solution of an indium salt. The precipitated form is yellow, and the salt formed by dry methods varies from yellow to brown. It is soluble in mineral acids, readily forms colloidal solutions, and gives complex salts with the alkali sulfides, such as K2In2S . 

Colloidal Metazirconic Acid. — On boiling, the hydrosol of zirconic acid changes to metazirconic acid. For the preparation of the meta acid, metazirconium chloride may be employed. This latter substance is made by repeated evaporation of the oxychloride. By dialyzing the solution a milky liquid is obtained that closely resembles meta-stannic acid. Concentrated HCl produces a precipitate that is soluble in water. Concentrated solutions of alkali chloride behave similarly. The hydrosol is completely precipitated by sulfuric acid and the pre-... 

The colloid is prepared by rapidly mixing dilute solutions of sodium thiosulfate and hydrochloric acid so that the final concentration of each is about 0.002 M. The following reaction then occurs so slowly that the sulfur precipitates only on those particles that nucleate first ... 

Historically, aqueous sulfur sols are related to the so-called Wacken-roder s solution which is obtained by reaction of H2S with SO2 in water at 0 °C and which contains polythionic acids as well as elemental sulfur besides other sulfur compounds (e.g., sulfate). For a detailed early investigation and vivid description of this mixture, see ref. [6] for more recent studies, see later. A compilation of 23 patents for the preparation of colloidal sulfur mixtures from the years 1931-1948 has been published by Meyer [7]. 

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