RAY CADMIUM AND ZINC NITRITES. 169 XV1.-Cadmium and Zinc Nitrites. By PRAFULLA CHANDRA RAY. IN view of the contradictory statements of the previous workers in this field it seemed desirable to undertake a fresh investigation of cadmium and zinc nitrites. At the outset it may be pointed out that so far as the nitrite-forming capacity of mercury and cadmium is concerned the ques-tion is not one of the basic character of the metal. Mercury,* which occupies the lowest position in group I I B (in the electro-potential series) yields a fairly stable normal nitrite because both its chloride and nitrite are very feebly dissociated in aqueous solution (RBy and Dhar T. 1912 101 966). Thomsen found that mercuric oxide with its equivalent of aqueous hydrochloric acid evolves 18,920 calories whereas with its equivalent of nitric acid it evolves only 6400 calories and to this difference he ascribes the reason that an aqueous solution of mercuric nitrate is completely converted into chloride by the addition of an aqueous solution of hydrochloric acid.Mercuric chloride in aqueous solution is again completely converted into the cyanide by the addition of hydro-cyanic acid. Cadmium hydroxide also behaves differently towards the ordinary mineral acids. Thus whilst zinc and magnesium hydroxides with hydrochloric hydrobromic and hydriodic acids, respectively give almost the same value for the heat of neutralisa-tion namely about 19,500 calories with cadmium hydroxide the heat of neutralisation goes on increasing. Thomsen regarded the behaviour of cadmium oxide towards the above acids as exceptional, and on that account he refused t o class cadmium hydroxide in the magnesium group ( I ‘ Thermochemische Untersuchungen,” 111 279 e t Sep.; also English translation by Miss Burke p.129). The anomalous behaviour of cadmium is now easily accounted for. Its haloids are more feebly ionised than those of zinc and magnesium under similar conditions of dilution. I n fact it may be laid down as a safe guiding principle that a metal the haloid of which shows comparatively poor conductivity in aqueous solutions may be expected to yield a corresponding normal nitrite because as a rule its nitrite is also feebly ionised. The case of cadmium has been chosen as a crucial one. Conductivity measurement.s of cadmium chloride have been carried out by several investigators but as their results show con-* The author has pointed out that mercury occupies & twofold position in the Periodic System (see T.1905 87 180 ; also Chem. News 1914 109 85 160 RBY CADMIUM AND ZINC NITRITES. siderable discrepancy a fresh measurement has been made. It will be seen on reference to table I (p. 161) that at a dilution of 10 litres the equivalent conductivity of potassium chloride is 134 a t 29O that of cadmium chloride is 53 whilst t h a t of cadmium nitrite is only 33. Both these circumstances conduce to the stability of the nitrite and it has thus been isolated as a norinal salt. Zinc nitrite which can exist only in dilute solution under similar conditions has a conductivity of 73 (Riiy and Dhar T.1913, 103 13). It is well known t h a t zinc chloride is so readily hydro-lysed that on the addition of water a turbid liquid is obtained, due t o the formation of the compound Zn(0H)Cl. Zinc nitrite solution is acid and on concentration the nitrous acid set free decomposes according to the equation and thus zinc nitrate is continuously formed. The residue even if the evaporation is conducted in a vacuum is thus found to be a basic nitrate. E X P E R I M E N T A L . Cad?niuni N i t 1. it e . 3HN02=HN03 + 2NO + 2H20, Pure recrystallised cadmium chloride and silver nitrite were triturated in a mortar water being added from time to time until the filtrate gave no indication of excess of either of the parent substances; it was then evaporated in a vacuum over mlphuric acid.Bright pale yellow crystals were obtained which dissolved readily t o a clear solution. Preparation I11 was the product of double decomposition between calculated quantities of barium nitrite and cadmium sulphate : I. 0.3465 gave 0.2474 CdS. Cd=55.53. 0.035 , 4.35 C.C. N (nitritic) a t 29O and 760 mm. N = 13.79. 11. 0.2740 gave 0.1926 CdS. Cd =54*66. 0.1387 ,, 111. 0*0820 gave 0.0582 CdS. Cd(NO,) requires Cd = 54.90 ; N = 13.73 per cent. Apart from the results of the analysis the fact t h a t the salt did not lose its lustre even in an exhausted desiccator proves t h a t i t is anhydrous. Lang ( J . pr. Chenz. 1862 86 299) however, assigns to it the formula CC~(NO,)~,H,O. Several preparations were undertaken but in oiily two instances was the evaporated mass found to be partly insoluble in water (compare Vogel, 16.4 C.C.N (by combustion) a t 26O and 760 mm. N=13*26. Cd=55*20 RAY CADMIUM AND ZINC NITRITES. 161 Zeitsch. cinorg. C'hetn. 1903 35 402). Cadmium nitrite is ionised to a far greater extent than mercuric nitrite (Rky and Dhar T., 1912 101 966) and the tendency towards the formattion of a basic salt is thus easily explained. c'o n cln c 1 iv i f g Mecis I I re m en f s. The chloride was purified by recrystallisation (0.4391 gave CdCl,,H,O requires CdCl,= 91.50 per 0.6284 AgCl ; CdCl = 91.43. cent. ) . TABLE I. E p z~ ivn 7 PW t Co 11 rlzt r t i c i t y of Cd C1 ,H20 CL t 2 9 * 5 O. 21 ............... 10 20 40 so 160 320 640 X ............... 63-53 (33.60 73-76 84.4 94.31 102.1 104.15 Epttivnlenf C o 7 i d u c f ~ i ~ i t y of Cd(NO,) at 29O.21 ............... 10 20 40 SO 160 320 640 1024 X ............... 33.7 43.9 55.1 67.1 78.3 88.3 96.1 104.6 Decomposition b y Heat. The method of heating has been described in detail in the case of the alkali nitrites (loc. c i t . p. 180). The sa,lt began to deconi-pose slowly a t 1 5 0 O . The temperature was gradually raised t o 165O and finally to 230° when the ' click ' remained persistent. The gas which was collected in the reservoir of the mercury pump was found to be pure nitric oxide it being completely absorbed by an alkaline solution of sodium sulphite. The alkaline liquid in the glass spiral was washed out and was found to consist of a mixture of nitrite arid nitrate in the following proportion: Nitritic nitrogen = 3.Ni tFa t ic nitrogen ~~ The brown residue was found to be cadmium nitrate mixed with cadmium oxide. As nitric oxide was the chief gaseous product the main portion of the salt evidently decomposed according to the equation 3Cd(NO,) = 2Cd0 j- Cd(NO,) + 4N0. Side by side a parallel decomposition goes on thus: Cd(N0,)2 = CdO + N,O (NO + NO,). Divers has shown t h a t when nitrogen peroxide mixed with an excess of nitric oxide is passed into a solution of alkali pure nitrite is thereby produced (T. 1899 75 86). I n the present instance, although there was a large excess of nitric oxide the conditions of reaction were not comparable. The gaseous mixture was no 162 FRIEND NOTES ON THE EFFECT OF bubbled through a liquid but was quickly drawn across the glass beads moistened with alkali hydroxide.Moreover Dixon and Peterkin have shown that “the peroxide enters into’ a limited combination with nitric oxide” (ibid. p. 629). A small quantity of nitrogen peroxide is absorbed as such giving rise to the forma-tion of a nitrate as well. Z i m N i t r i t e . The salt was prepared by double decomposition between mole-cular proportions of zinc sulphate and barium nitrite. The filtrate, on evaporation in a vacuum left a white swollen mass which was practically insoluble in water. There was a thin membrane coat-ing the surface which on being broken up evolved nitrous fumes. During the concentration of the liquid nitric oxide was continu-ously evolved a portion of which remained imprisoned inside the thin superficial coating. The residue was boiled with a solution of pure sodium hydroxide and the alkaline liquid was found t o be free from nitrite and to contain only nitrate It will thus be seen that zinc nitrite solution on evaporation to dryness leaves a residue only of a basic nitrate. CHEMICAL LABORATORIES, PRESIDENCY COLLEGE AND COLLEGE OF SCIENCE, UNIVERSITY OF CALCUTTA [Received Februnrp lst 1917.