Selenic acid and iron.—Reduction of selenic acid by nascent hydrogen and hydrogen sulphide.—Preparation of ferrous selenate and double selenates of iron group

Exceptional difficulties have been met with in the preparation of the iron (ferrous) group of double selenates of the monoclinic isomorphous series R2 M (S Se O4 )2 , 6H2 O, and some new and unexpected chemical facts have been revealed, which form the subject of this communication. When the author, in pursuing the course of the crystallographic and physical investigation of the double selenates of this grand series on exactly parallel lines to those followed in the completed investigation of the corresponding double sulphates, arrived at the iron group, three difficulties were encountered. The first was that of preparing the simple salt ferrous selenate, common to the group. The second was the rapid decomposition, with brown deposition, of the aqueous solution of any ferrous selenate obtained, also that of the mixed solution obtained by adding to the latter solution a solution of the molecular equivalent of the alkali selenate, with the object of preparing any one of the four salts of the group, K2 Fe(SeO4 )2 , 6H2 O, Rb2 Fe(SeO4 )2 , 6H2 O, Cs2 Fe(SeO4 )2 , 6H2 O, (NH4 )2 Fe(SeO4 )2 , 6H2 O. The third difficulty was offered by the fact that no crystals of the potassium ferrous salt were ever obtained at all. The author's first efforts to obtain these salts were made eight years ago in the cases of the potassium and rubidium salts. The result was that, under conditions which were obscure, but undoubtedly included a moderately low temperature, it being winter time, one excellent and permanent crop of rubidium ferrous selenate was obtained, the small quantity employed of the ferrous selenate considerable quantity of moderately dilute selenic acid on much iron wire, the action being very slight. All other solutions of the constituents of this salt, and all the solutions of the constituents of potassium ferrous selenate, decomposed with much brown ferric precipitation, and no trace of the potassium salt crystals was ever obtained.