VI. Monoclinic double selenates of the nickel group

• Published in: Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1918
• Subjects: Rath; Carbonic acid
• Online Access: http://dx.doi.org/10.1098/rsta.1918.0006; https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.1918.0006

This communication deals with the four double selenates of the series R 2 M (SeO 4 ) 2 . 6H 2 O, in which M is nickel and R is potassium, rubidium, cœsium, and ammonium. Potassium nickel selenate and ammonium nickel selenate only have been previously investigated, and to a very limited extent, by Vom Rath and Topøse and Christi; rubidium nickel selenate and caesium nickel selenate do not appear to have formed the subject of either goniometrical or physical investigation. Great care has been taken with the preparation of the four double salts in a state of purity. The solutions in pure water from which the crystals were deposited contained in each case the two simple constituent salts in exactly equal molecular proportions. Good crystallised specimens of potassium selenate and ammonium selenate were already in the author’s possession, and the selenates of caesium and rubidium were prepared by dissolving the pure carbonates of the two metals in the exact quantity of pure selenic acid, all trace of carbonic acid being removed by boiling. The nickel selenate was prepared in the four cases separately, by dissolving in pure water the quantity of nickel sulphate corresponding molecularly to the amount of the alkali selenate to be used in the preparation of the double salt, and adding a very slight excess of caustic potash solution (freshly prepared from the weighed quantity of solid potash) in order to precipitate all the nickel as nickelous hydrate. After warming, so as to complete the precipitation, the liquid was allowed to stand until the precipitate had settled, when it was washed with a large volume of water, six times by decantation and six further times on the filter. The nickelous hydrate was then dissolved in the calculated amount of selenic acid, the filtered solution of nickel selenate was added to the alkali selenate solution, and the whole allowed to crystallise in successive crops by spontaneous evaporation, with all the precau­tions indicated on p. 9 of the author’s‘ Crystallography and Practical ...