1546 MALLET : ISOMETItIC: ANHYDROUS CLIV.-lsometric Anhydro,us Sulphates of the Form M”SO,,R’,SO,. By FREDERIC R. MALLET. IN a paper which appeared in March, 1900 (Trans., 77, 216), I de- scribed a series of isometric anhydrous sulphates having the common formula 2MSO,,R’,SO,, that were produced by fusing the constituent sulphates together in the proper molecular proportions. Since this paper was published, further experiments have led to the production, by similar means, of the isometric sulphates described below, which are allied t o those just alluded t o in their mode of crystallisation, but differ in their composition, one molecule only of the bivalent metal sulphate being present in them instead of two. Several sulphates of the constitution represented by M”SO,,R’,SO, have been previously described, the best known being perhaps the calcium sodium salt, which occurs naturally as the monoclinic mineral glauberite,” and has also been made artificially, both by fusion and in the wet way.So far as I have been able to ascertain, however, with the exceptions mentioned below in connection with the sulphates MgSO,,K,SO, and NiSO,,K,SO,, no account of the sulphates belong- ing to the isometric series, noticed in the present puper, has hitherto appeared, although the monoclinic hydrated congeners of most of them, M”SO4,R‘,SO,,6H,O, have been the subject of elaborate investi- gation, of late years especially by Tutton (Trans., 1893, 63, 337; 1896, 69, 344). I t is unnecessary to allude to the details of the method adopted for producing and examining the salts with which the present communica- tion is concerned, because such details are similar t o those already described in connection with the sulphates 2M’SO4,R’,S0,.* As laiigbeinite is the only mineral known as yet haviiig the formuIa 211z”S@,, R’,SO,, so glsuberite is the only one corresponding to M”SO!, R’,S04.SULPHATES OF THE FORM M”YO,,R’,SO,. 1547 The products obtained, whilst substantially isotropic, generally in- cluded more or less birefringent material. In some cases, only a few isolated specks of the latter were noticeable, which might be attributed to the original mixture of sulphates not having been in perfect molecular proportion, or to the proportion being slightly altered, during fusion, by elimination of sulphur trioxide, whereby a minute excess of R’,SO, was induced.I n other instances, the proportion was greater : though always quite subordinate, it was found to vary considerably in the same double salt as produced by different fusions, presumably owing to slight variations in the conditions of cooling. More commonly, the birefringent part was so intimately intercrystallised with the main mass as to be inseparable, but from certain specimens of three salts, MgSO,,Rb,SO,, MnSO,,Rb,SO,, and NiSO,,K,SO,, i t was possible to isolate, in a fairly pure condition, a sufficiency of the accompanying birefringent material for the estimation of one or other constituent, from which the composition of the substance could be calculated. The results gave the respective ratios, M”S0, : R‘,SO,= 2 : 3.07 ; 2 : 2.91 ; 2 : 3.21, or 2 : 3 nearly.On fusing the mixtures ZMgSO, + 3Rb,SO, ; 2MnS0, + 3Rb,SO,, and 2NiS04+3K,S0,, as a check on the above figures, the products obtained were all birefringent. The occurrence of similar products, mixed with the salts M’SO,,R’,SO,, is perhaps due in some instances to a small proportion of the solidifying material crystallising in accordance with the equation 4(M’S04 + R’,SO,) = 2~~”S0,,3R’,S04 + 2MS0,,R’2S0,. Where the las t-mentioned salt is isometric, in common with the corresponding sulphate M”SO,,R’,SO,, it would easily escape recognition when intercrystallised in trivial proportion through the great mass of the latter. But there are, of course, other conceivable modes in which the sulphate 2M‘SO4,3R,SO, might be balanced.That the occurrence of such birefringent substance, in the cases where it admitted of being separated from the main mass, at least, did not materially affect the composition of the latter, is shown by the following estimations : Main mass. SO,, found. SO,, required. MgSO,,Rb,SO,. .............. 41.51 41.35 per cent. MnSO,,Rb,SO,.. ............. 38.46 38.31 ,, NiSO,,K,SO, ............... 48.68 48.67 ,, The sulphur trioxide was not estimated in the remaining salts. In some there was practically no birefringent material, and in cases where it was inseparable from its host, the percentage of sulphur trioxide would necessarily equal the theoretical amount, experimental error and loss through decomposition of MSO, during fusion excepted. That the latter was insignificant could easily be seen by dissolving the double salt in water, when, generally, there was a mere trace of1548 MALLET : ISOMETRIC ANHYDROUS oxide as residue.Thus the residue left by the nickel potassium salt, which was greater than that of most of the others, only amounted to about 0.1 per cent. The crystals employed for measurement were, in some cases, very minute, and it mas not always practicable t o isolate and mount a single individual, so t h a t two or three crystals in parallel position were sometimes unavoidably used, Owing to this, and also to the faces, in some instances, having lost more or less of their original brightness, through incipient hydration on the Surface, the images available were not always satisfactory. To this cause may be ascribed, in part at least, the differences between the measured and calculated angles.A comparison of the details given respecting the isometric salts M”SO,,R,’SO, and 2WS04,R,’i30, shows that, with the doubtful ex- ception of MnSO,,Tl,SO,, the sulphates of the first-mentioned series crystallise in tetrahedral forms only. While the same is true in respect t o some salts of the composition 2MS0,,RiS04, in the crystals of others rhombic dodecahedra1 planes are present, and those of 2CoS0,,K,S04 are further modified by faces of the Cuba. Mugnesiurn Potassiune SulpT~ccte, Mg SO,, K2S04. The salt crystallises in tetrahedrons, which are more commonly unmodified, but are sometimes in combination with the tetrahedron of opposite sign, the planes of the latter, however, being usually sii5ordinate in their development : Measured.Calculated. 111 A iii ............ 109032’ 109’28’ The crystals generally (but not always) form groups, within each of which the orientation is parallel. As the most frequent result of this tendency, the individuals are arranged in columns of interpenetrant tetrahedrons with their centres in line, the columns themselves also being sometimes parallel t o each other. Compound tetrahedrons like- wise occur that are of large six0 compared with the individuals of which they are built up. The weight of a powdered sample so treated, while still slowly rising, after five months had increased by 3.41 per cent. only. For conversion into the salt MgSC),,K,SO,,GH,O, the percentage would be 36.69. Anhydrous magnesium potassium sulphate has been produced by Berthelot and Ilosvny through fusion of the constituent sulphates together (Ann. Chim.P?hys., 1883, [v], 29, 329), but as the crystallo- graphic character of the substance is not alluded to in their memoir, being foreign to the scope of their work, the salt is included amollgst, those here described. The salt absorbs water very slowly when exposed to the air.SULPHATES OF THE FORM M”SO,,R’,SO,, 1549 Magnesium Rubidium Sulphate, MgSO,, Rb,SO,. The tetrahedrons formed by the crystals are sometimes unmodified, but are most frequently in combination with the tetrahedron of oppo- site sign, the latter being generally subordinate : Measured. Calculated. 111 A 111 ............ 70’34’ 70’32’ 111 A 111 ............109031’ 109’28’ The faces are sometimes cavernous, in some cases so much so that the crystals become skeletons, Similar cavernous faces were also noticed on the faces of some of the other salts, although scarcely to such ar? extreme degree. More than three trihedral angles of any individual tetrahedron are rarely exposed to view, but of these, in some crystals, only two are truncated by planes of the opposite tetra- hedron; the crystal then, when the faces of the two tetrahedrons are equally developed, being equivalent to an octahedron with two opposite sides wanting, which is, geometrically, a rhombohedron. There is a very strong tendency to crystallisation in parallel position, in modes similar to those affected by the preceding sulphate. The salt becomes slowly hydrated on exposure to the air in powder.After seven months (with a still increasing weight), 8.02 per cent. of water had been absorbed by the portion experimented on, the theoreti- cal amount for conversion into the hexahydrated sulphate being 27-91. Munganous Pot am ium Sulphate, MnSO,, K,SO,. The salt is reddish-white, and forms crystals quite similar to those of magnesium potassium sulphate, both in the relative frequency of occurrence, and degree of development, of the + and - tetrahdral planes, and also in the modes according to which the crystals group themselves in parallel position : Measured. Calculated. 111 A i i i ............ iogom’ 109’28’ This salt resembles the sulphnte 2MnS04,K2S0, in its stability when exposed to the air. After 44 months’ exposure of a pulverised sample, the absorption of water, which varied with the weather and was evidently hygroscopic, never exceeded 0.17 per cent.Mangunourr Rubidium Xulphate, MnS04,R b,SO,. The crystals are reddish-white, and similar to those of magnesium rubidium sulphate in the relative frequency of occurrence, and degree of development, of the i- and - tetrahedrons, and likewise in the1550 MALTJET : ISOMETRIC ANHYDROIJS occurrence of pseudo-rhombohedrons. due to the elongation of the crystals parallel to a tetrahedral edge : Another mode of distortion is Measured. Calculated. 111 A i T i ............ 109033' 109'28' There is a very strong tendency to grouping in parallel position after the modes previously alluded to : the product of one particular fusion showed faces of compound tetrahedrons with sides nearly a centimetre long.On treating it portion of the salt in the same may as in the preceding case and for the same period, the water absorbed at no time exceeded 0.51 per cent. Manganous Tl~mZZous Xulplmte, MnSO,,Tl,SO,. Manganous thallous sulphate is reddish white. The tetrahedral crystals are sometimes unmodified, but usually the + and - forms are both present, one being predominant. Their relative devaopment, however, varies much, and (geometrically) octahedral crystals are by no means rare : Measured. Calculated. 111 A iii ............ 109027' 109O28' 111 A in ............ 70027' 70'32' The free (top) surface of cooling, besides a multitude of facets obviousIy belonging to crystals like those just mentioned, generally showed a small proportion of square or short rectangular facets, suggestive of cubic crystallisation.No actual cubic crystals, however, were noticed, or any cubic faces replacing tetrahedral edges. There is a strong tendency to grouping in parallel position. On treating a portion of the salt like the corresponding potassium sulphate, and for the same length of time, the weight fluctuated, with a maximum increase of 0.52 per cent. only. Nickel Potassium Subhate, NiSO,,K,SO,. This sulphate is mentioned by Gmelin (Handhuch der Chemie, 3, 360), without allusion, however, to its mode of crystallisation, It is yellowish-brown when hot, yellow after cooling, and cry stallises in unmodified tetrahedrons : M.easured. Calculated. 111 A i i L ......... 109'29' 109'28' The crystals generally show a strong tendency to grouping in paraliel position, after the modes already described, but sometimes the orientation is quite irregnlar.SULPHATES OF THE FORM M”so,,R’,so,, 1551 The anhydrous salt is converted, comparatively quickly, into the hydrated sulphate, NiS0,,K2S0,,6H,0, on exposure to the air for a sufficient length of time.A pulverised sample so treated until the weight no longer increased absorbed 32.17 per cent. nf water, six mols. requiring 32.85. Cobaltous Potasoium XuZphccte, c‘oS0,,K,S04, Cobaltous potassium sulphate is violet when not, and violet-crimson after cooling, and occurs in unmodified tetrahedrons : Measured. Caleula ted. 111 A iii ............ 109032’ 109O28’ The nickel and cobalt salts are very similar in their tendency towards parallel orientation, Like the last-mmtioned sulphate, that of cobalt changes somewhat rapidly on exposure to the hexahydrated salt, While the theoretical percentage of water required is 32-82, an absorption of 32.05 was obtained experimentally, The sulphates of the following metals mere also fused together, in the same molecular proportion as the preceding : - I L - Z n + K L - Ni+Rb Co+Rb Zn+Rb Mg+Cs Mn+Cs Ni-FCs Uo+Cs Zn+Ca Mg + T1 - Ni+T1 Co+T1 Zn+T1 The resulting products were all of non-isometric crystallisation, as shown, in most cases, by their external characters, and in all by their birefringence. Whilst many of them, at least, afforded no obvious indication of the two sulphates being in other than homogeneous com- bination, it would be unsafe to regard such homogeneity as proven without a .more detailed examination of the products than I have given to them.