The patented methods of making manganese arsenates for insecticidal use consist in treating a manganese compound, such as pyrolusite, with white arsenic (As2O3) in the presence of nitric acid as a catalyst. The manganous arsenate formed is partly converted to the trimanganoarsenate by treatment with manganese carbonate to lower the water soluble arsenic content. The brown color of the insecticide is produced by treating the mixed arsenates with lime, which decomposes some of the arsenates with the formation of calcium arsenate and hydrated oxides of manganese. Burnt umber is also generally added to cheapen the product. The chemical analysis of the commercial insecticide shows that the total arsenic content runs close to 40 per cent calculated as arsenic pent oxide As2O5; that the water soluble arsenic content ranges from 0.7 arsenic pent oxide As2O5; and that the total manganese calculated as to 1.5 per cent calculated as manganous oxide (MnO) ranges from 31.6 to 40.7 per cent. The lime content, present mostly as calcium arsenate, ranges from 15.5 to 16.4 per cent calculated as calcium oxide (CaO). The commercial manganese arsenate insecticide is a complex mixture of various arsenates of manganese, calcium arsenate, oxides of manganese and smaller quantities of aluminum, iron, silica, etc. The composition of different samples is not the same.
Document Type: Research Article
Publication date: June 1, 1930
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