326 RAY: THE DOUBLE NlTRITES OF MERCURY AND THEBy PRAFULLA CHANDRA RAY.IN a previous communication a general method of preparation ofthe double nitrites of mercury and the alkali metals has been described(Trans., 1907, 91,2031). Recentlyit has been found that this methodis equally applicable to the preparation of the corresponding mercuriccalcium, mercuric strontium, and mercuric barium nitrites. For instance,if a solution of calcium nitrite is added to a perfectly clear solution ofmercuroso-mercuric nitrite, ( HgN02)2,4Hg(N02)2, almost immediateturbidity is caused, due to the separation of metallic mercury i n a finestate of division. The explanation already given (Zoc. cit.), namely,that '' the process of dissociation is accelerated because of the tendencyof one of the products of dissociation, namely, mercuric nitrite, tounite with the alkali nitrite," adinits of further amplification.It isthe tendency t o form complex ions that is really the rnotay of thereaction. A solution of potassium mercuric nitrite, K2Hg(N02),,contains mercury, not as a cation, but as part of a complex bivalentanion, Hg(N02),.* Hence, such a solution behaves as a neutral one,and can be diluted ad injinitzcrn without undergoing the hydrolysis, socharacteristic of the oxy-sal ts of mercury, for example, mercuricnitrate. This also explains the eingular behaviour which I noticedsome twelve years ago (Zeitsch. anorg. Chem., 1896, 12, 367), namely,that carbamide does not precipitate the mercury from the solution,or a solution of sodium sulphate give the characteristic precipitate ofturpeth mineralMethod of Prepamtion.-The light yellow solution of the doublenitrites is evaporated under diminished pressure over sulphuric acid.As a rule, crystallisation of the salts does not take place, buta syrupy liquid is obtained, which, on being stirred with a rod,solidifies entirely, with the formation of mealy crystals and liberationof heat. I n fact, the characteristic behaviour of supersaturatedsolutions is noticed. As the crystals were very soluble, they werewashed with the minimum quantity of water, and dried by pressurebetween folds of bibulous paper. If the salts are preserved in a,stoppered bottle without being well dried, they slowly decompose, withevolution of nitrous fumes ; but if they are kept in the open bottlein the desiccator, they remain perfectly stable (compare mercuricDer Quecksilbernitrit=komplex " (Diss., Breslau, 1906).* Hans Pick, " Beitrage zur Characteristik des Nitrit-ionsMETALS OF THE ALKALINE EARTHS.327nitrite, Trans., 1904, 85, 524). The compounds described belowcontain five molecules of water of crystallisation.Mercuric Calcium Nitrite.Found : Hg = 38-21 ; Ca = 7.96 ; N = 10.98.N = 10.90 per cent.Hg(NO2),,Ca(N0,),,5H2O requires Hg = 38-9 1 ; Ca = 7.78 ;Mewxwic Strorthunz Nitrite.Found : Hg = 44.58 ; Sr = 13.08 ; N = 11-17.N = 10-57 per cent.3 Hg(N02)2,2Sr(N0,),,5LI,0 requires Hg = 45.31 ; Sr = 13.18 ;Mercu& Bayium ATitrite.Found : Hg = 39.88 ; Ba == 19.80 ; N = 10.55.3Hg(N02)2,2Ba(N0,),,5H,0 requires Hg = 42.13 ; Ba = 19.24 ;N = 9.84 per cent.The preparation of the last two salts was repeated, but the com-position was practically constant.The low percentage of mercuryand the proportionately high percentages of barium and of nitrogenin the last one are probably due to the substance being invariablycontaminated with traces of mother liquor containing excess ofthe nitrites of the latter metal.On comparing the whole series of double nitrites, it is of interest t onote that the power of mercuric nitrite to unite with the nitrites ofthe alkali metals is the greater the less the atomic weights of thelatter, Thus, mercuric nitrite can combine with four molecules oflithium nitrite and with three molecules of potassium nitrite, althoughit also forms characteristic stable compounds vith two molecules ofeither sodium or potassium nitrite. On the other hand, it com-bines molecule for molecule with calcium nitrite. Again, onemolecule of mercuric nitrite can combine with only two-thirds of amolecule of strontium or barium nitrite. Cryoscopi:: determinationsof the molecular weights of the above salts have been undertakenwith the view of throwing light on their constitution, the results ofwhich I hope to communicate shortly.CHEMICAL LABORATORY,PREhIUENCY COLLEGE, CALCUTTA