Watson, Cole, Grindle & Watson
Method for manufacture of arsenious anhydride
 Arsenic anhydride of high purity is inexpensively manufactured from an arsenic sulfide-containing substance by first contacting the arsenic sulfide-containing substance with a copper sulfate-containing aqueous solution so as to provide an extract solution containing arsenious acid, the extract solution is subjected to aeration in the presence of copper ions such that the arsenious acid therein is mostly oxidized to arsenic acid, the thus provided treated solution is subjected to a weak reducing agent to cause crystals of arsenious anhydride to form, and these crystals are then recovered. Alternatively, the extract solution is cooled to recover a solid precipitate containing arsenious anhydride, these solids are repulped into a slurry, the slurry subjected to aeration in the presence of copper ions such that the arsenious acid therein is mostly oxidized to arsenic acid, the thus provided treated solution is subjected to a weak reducing agent to cause crystals of arsenious anhydride to form, and these crystals are then recovered. 
Sumitomo Metal Mining Company Limited
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Hiroyuki Tadashi Naoki
Tamura Nakano Kubo