48 VIL-On the Grystallised Hydrates of Baryta and Strontia BY CHARLESL BLOXAM. CONSIDERABLE difference of opinion appears to exist among chemi- cal authors with respect to the composition of the crystallised hydrates of baryta and strontia some representing them as contain- ing 8 eqs. others 9 eqs. and others even 10 eqs. of water whilst in some cases these hydrates so closely analogous in their chemical relations are represented as crystallising with different amounts of water. Having had occasion to satisfy myself with respect to their true composition I beg to submit the results of my analysis to the Society. The crystallised hydrate of baryta was prepared according to the method recommended by Mohr by adding powdered nitrate of baryta to a boiling solution of an equivalent quantity of hydrate of soda.The crystals which separated from the cooled liquid were purified by two crystallisations. On examining the solution from which the first crop of crystals had been deposited it was found to contain a considerable quantity of undecomposed nitrate of baryta together with some hydrate of soda showing that the decomposition of the nitrate by a single equivalent of soda was far from complete. In a second preparation 1.4 eqs. of hydrate of soda were employed but in this case also a considerable quantity of the nitrate of baryta was left undecorn- posed though less than in the first experiment. The hydrate of baryta exhibited in a remarkable degree the tendency to remain without mystallising in a super-saturated solution until it was either briskly stirred or placed in contact with a crystal of the hydrate.On attempting to dry the crystals in vacuo over oil of vitriol they soon became opaque which was at first attributed to the for-mation of a thin film of carbonate but was afterwards found to arise from loss of water; indeed the crystals were found to effloresce even in air of ordinary humidity which may help to explain the discrepancy in the results which they have afforded to different analysts. CRFSTALLISED RPDRATES OF BARYTA AXD STRONTIA 49 In order to determine the amount of water lost in vacuo over oil of vitriol separate samples of the crystals obtained in two dis- tinct operations mere exposed in a receiver of air over quick lime and weighed at short intervals until the loss of weight in a given period suddenly diminished and the first sign of efflorescence began to show itself upon the edges of the crystals.Two determinations of adhering water made in this way gave respectively 1.39 and 1-24per cent. The dry crystals were then exposed in vacuo over oil of vitriol until they ceased to lose weight. The effloresced hydrate thus obtained was heated to dull redness in a closely covered silver crucible and weighed at intervals of four or five minutes until it began to increase in weight slightly, from absorption of carbonic acid. The baryta was also precipitated and determined as sulphate both in the original dry crystals and in the effloresced hydrate.The subjoined table contains the results of these experiments calculated for 100 parts of the dry crystallised hydrate. Calculateil (Ba = 685) I I1 111 IV V VI Mean. Ba0,HO + HO + 7Aq. Water lost in V~CUO 3936 39 30 39 69 39.84 39.63 39.56 po.00 , , on ignition 5 93 6 04 6.12 6.03) 45'59 5-71) 45*'i1 Baryta 48'12 48-42 48.26 48-26 48.57 These numbers appear to warrant the conclusion that the formula of the crystallised hydrate of barpta is Ba0,HO + 8Aq. and that of the efloresced hydrate Ba0,HO + Aq the pure hydrate Ba0,HO being obtained by igniting the latter. The effloresced hydrate suffered no more loss of water at 21.2"F even in vacuo. It is worthy of iiotice that this effloresced hydrate evolved much beat when moistened with water.The crystallised hydrate of strontia was also prepared by decom- posing the nitrate of strontia with hydrate of soda at the boiling point; in this case nearly 2 eqs. of the hydrate mere employed for each equivalent of nitrate of strontia and this salt was found to have been completely decomposed. The hydrate of strontia how-ever did not dissolve in the liquid like the hydrate of baryta but separated in the form of a granular precipitate which had the same composition as the crystallisecl hydrate. On pouring off the solution containing the nitrate of soda and boiling this granular precipitate with successive portions of water very large and beau-T'OL. XI'II. E 50 BLOXAM ON CRYSTALLTSED RYDRATES OP BARYTA &c. tiful cry&& were obtained which were purified by recrystallisa- tiOD.The crystals effloresced in the same way as those of hydrate of bavyta. They were analysed in a similar manner the strontia beiag completely precipitated by sulphuric acid and alcohol and the sulphate of strontia subsequently washed with alcohol. The results are seen in the following table. Calculated (Sr = 43%) I 11 111 IV Mean. 47 '77 16040 SiQ,€IO + HO -i-7hq Water lost hvacuo . . . 4779 4775 ;:::)-61-00 , , on ignition . . . 19-61 12 65 12-63 t%mntf . . . . 39.18 39.04 3912 3906 39 00 It appears then as would be expected that the formula of the crystallised hydrate of strontia is Sr0,HO + 8Aq and that of the effloresced hydrate Sr0,HO + Aq but that when this latter is heated to dull redness it loses the whole of its water anhydrous strontia being left.* 'The effloresced hydrate did not lose any more water in the water-oven at 212' F but when raised to this temperature in vacao it lost 12-89 per cent.or exactly one equivalent of water thus becoming converted into the simple hydrate Sr0,I-KO.? Both this and the effloresced hydrate evolved heat when moistened with water. The inferio;. power possessed by strontia to retain these two last equivalents of water is another interesting example of the gracla-tion constantly observed in the properties of baryta and strontia; and I must express my regret that want of leisure precludes me for the present from examining tlic crystallised hydrate of lime which may be expected to occupy a still lower position iyith respect;to its power of retaining water of crystallisatiou. * I fmd that %his circamstance had been already pointed out by Den4am Smith (Phil. Mag. [3] ix 87) although chemical writers have still represented the hydrate ofofBtrontiaas permanent at a red heat. + The effloresced hydrate also lost nearly the whole of its second equivaIent of water when exposed for a very long time over very concentrated oil of vitriol in VllCUO.