IODATES AND PERIODATES OF THE ALKALI METALS 1511.-Note on the Iodates and Periodates of the AlkaliMetals and the Ammonium Radicle.By THOMAS VIPOND BARKER, B.A., B.Sc.(Oxon.).THE present communication deals with the chemicaI part of aninvestigation of certain iodates and periodates which were chiefly pre-pared for a crystallographic examination ; the results of the latterwill appear shortly in the Zeitschrift fur Krystaztographie.Of the analyses, the halogen estimations were effected by the Cariusmethod, which the author had previously found to answer well for theperchlorates; the heating was carried out in two operations, eachlasting four hours, the first to 150' and the second to 250'. Themetal was estimated by the usual sulphate method.The specific gravity determinations were made in capped specificgravity bottles with carbon tetrachloride as displacing liquid ;the solubility determinations mere carried out with 20 C.C.of thesaturated solutions.Kubidium lodute, RbIO,.-This salt, as well as the correspondingcasium compound, was first prepared by Wheeler (Amer. J. Xci., 1902,[iii], 44,123) by adding iodic anhydride to solutions of the carbonates.A good yield is obtained by passing chlorine into a hot concentrate1 6 BARKER : NOTE ON THE IODATES AND PERIODATES OF THEsolution of a mixture of rubidium iodide and hydroxide, wherebythe sparingly soluble iodate is precipitated :Specific gravity at 14"/4" = 4.559.Solubility : 100 parts of water dissolve 2.1 parts at 23" (WheelerCaesium lodale, CsIO,.-This salt was prepared in the same way asSpecific gravity a t 16'/4O= 4,831.Solubility : 100 parts of water dissolve 2.6 parts at 24' (Wheeler).The iodates of potassium, rubidium, and cesium form anisomorphous group, crystallising in what appear to be cubes, butwhich are really made up of four monoclinic sub-individuals, inter-penetratingly twinned.Potassium periodate, KIO,, is readily prepared by oxidising theiodate; a suitable method is to pass chlorine into a hot, stronglyalkaline solution of the iodate (Rammelsberg, Ann.Y l ~ y s . Chern.,1868, [ii], 134, 368) ; the very sparingly soluble periodate separatesin tetragonal bipyramids * :Mol. vol. = 57.14.the rubidium compound :Mol. vol. = 63.68.0.3080 gave 0.3106 AgT.Specific gravity a t 15"/4"= 3.618.Solubility : 100 parts of water dissolve 0.66 part at 13O, and thespecific gravity of the saturated solution at 13'/4" is 1.0051.Rubidium periodate, RbIO,, has not previously been obtained.Itwas prepared by the method mentioned above for the potassiuuicompound. The precipitated crystals mere washed and recry stnllisedtwice :I= 5 4 5 .KIO, requires I = 55.1 per cent.Mol. vol. = 63.60.0.3090 gave 0.2664 AgI.0.4045 ,, 0,1930 Rb,SO,. Rb = 30.54.RblO, requires I = 45.9 ; Rb = 30.91 per cent.The high value for iodine and the low value for rubidium point tothe presence of a small amount of potassium. The salt formsbeautiful, colonrless, tetragonal crystals, strictly isomorphous with thepotassium compound :I = 46.6.Specific gravity at 16'/4'= 3.918.Solubility: 100 parts of water dissolve 0.65 part at 1 3 O , and theMol.vol= '70.56.specific gravity of the saturated solution at 16'14' is 1.0052.* Potassium periodate was stated by Ranimelsberg to bc orthorhonibic and iso-niorl)hous with the perchlorate, but, iii spite of all efforts, the author did notsucceed i n obtaining an olthorhombic modification, so he communicated with Prof.Groth, of Munich, who fortunately had i n his possession the preparation originallymeasured by Ranimelsberg. Prof. Groth kindly had the crystals andysed, and theywere found to contain 110 trace of iodine, being, in fact, practically pure potassiuiiiperchlorateALKALI METALS AND THE AMMONIUM RADICLE. 17Cccesium periodate, CsIO,, was first prepared by Wells (Amer.Chem,.J., 1901, 26, 278) by neutralising periodic acid with cwsiumcarbonate. The salt may also be prepared by the chlorine method,but the yield is by no means good, much iodate precipitating with thecrystals of the periodate; the bulk of the author's salt was thereforeobtained by Wells's method :0.4601 gave 0.3321 AgT. 1=39*02.CsIO, requires I=39*20 per cent.Cesium periodate is fairly soluble in water, and crystallises in well-defined plates belonging to the orthorhombic system, and is thereforenot isomorphous with the potassium and rubidium compounds :Specific gravity at 15"/4'= 4,259.Solubility : 100 parts of water dissolve 2-15 parts a t 15", and thespecific gravity of the saturated solution a t 15'/4' is 1,0166.Ammoniunt periodate, NH,IO,, was obtained by neutralising asolution of periodic acid prepared by Wells's method (Eoc.cit.) withaqueous ammonia; the salt is isomorphous with the potassium andrubidium compounds :Mol. vol. = 76.04.Specific gravity a t 18'/4O= 3,056.Solubility: 100 parts of water dissolve 2-70 parts at 16', and thespecific gravity of the saturated Bolution at 16'/4O is 1.0178.Sodium periodate, NaIO,, crystallises in two forms : one anhydrous,isomorphous with the ammonium salt; the other with 3 molecules ofwater, in the rhombohedra1 system :Mol. vol. = 68.39.Specific gravities : NaIO, at 16'/4O- 3,865.The periodates of potassium, rubidium, ammonium, sodium, as wellas of silver and lithium (accoiding to Rammelsberg) form therefore anisomorphous group, crystallising in the tetragonal system. The groupis interesting, not only because the majority of the elements in thefirst group of the periodic classification are represented, but alsobecause the crystalline form is extraordinarily similar to that of theminerals of the scheelite group. The cause of this is, no doubt, to befound in the similarity of the type of composition, KIO,,CaWO,, justas it is in certain othor pairs of compounds, for example, calciumcarbonate and sodium nitrate, and potassium perchlorate and bariums ulpha t e.Mol. vol. = 55.37.97 NaI0,,3aq. at 18'/4'= 3.219. Mol. vol. = 83.28.The author's thanks are due to Prof. H. A. Rliere, in whoselaboratory the above work was carried out.hIINERBLOGICAL DEPARTMEN'r,OXFORD.UNIVERSITY MUSEUM,VOL XCIII.