37 General and Physical Chemistry. Refractive Indices of Liquid Nitrogen and of Air. By G. D. LIVEING and J. DERAR (Phil. Mag., [ 5 ] , 36,328-331).-The authors have determined the refractive indices of liquid nitrogen and air, using Terquem and Trannin's method of suspending in the liquid two parallel glass plates with a thin layer of air between them, and measuring the angle of incidence at which the ray suffers total reflec- tion at the surface of the air. The liquid nitrogen was contained in a, vacuum-jacketed tube, the liquid acting as a lens, and the source of light and the spectroscope-slit being conjugate foci when the liquid was mid way between them. The glass plates were separated by a ring of thin filter-paper, thoroughly wetted with white of egg, and allowed to dry, and were attached to a rod which formed the prolongation of the vertical axis of a theodolite used to measure the angle through which they were turned. The apparatus gave €or liquid oxygen, p D = 1.226, slightly larger than the value obtained by the authors with a prism, namely, 1.2236.For nitrogen which contained 5 per cent. of oxygen, the refractive index was found to be pD = 1.2053 at -190", and for air, pD = 1.2062. The refraction constant for liquid nitrogen, according to Gladstone's formula, is 0.225, and the refraction equivalent, 3.153 ; according to Lorenz's formula, these values become 0*14i4 and 2.063 respectively. Polarisation of Platinum Electrodes in Sulphuric acid. By J. B. HENDERSON (Proc. Boy. Xoc., 54, 77--82).-Of two platinum electrodes immersed in sulphuric acid and connected with the primary circuit, one was also connected with the earth, and the other through a key with one pair of quadrants of an electrometer.Connected with the same pair of quadrants, through another key, was the slider on a bridge with a special battery. The other pair of quadrants and one end of the bridge were earthed. The slider was so moved that the permanent deflection it gave on the electrometer was not disturbed when the primary circuit was broken and the polarised electrodes connected with the instrument. The potential of the quadrants was then that of the polarisation. The mean value of the electromotive force of polarisation determined in this way was 2.09 volts, the primary current varying from 0.2 to 1.0 amp,, the time of its passing from 25 minutes t o 15 hours, and the strength of the solutions from 5 to 30 per cent.Use of Cupric Nitrate in the Voltameter and the Electro- chemical Equivalent of Copper. By F. E. BEACH (Arner. J. ~Tci., [3], 46, 81--88).-The object of this paper is to show that cuprie nitrate has some marked advantages over the sulphate for use in the voltameter. The nitrate solution freshly prepared has a tend- ency to dissolve copper, which decreases, however, after the copper J. W. The extreme values were 2.05 and 2.14. J. W. VOL. LXVI. ii. 538 ABSTRACTS OF OEEMIOAL PAPERS. electrode has been kept in the solution for a sufficient length of time. Another difficulty is due to oxidation of the copper deposited, which may be prevented by the addition of a, small amount of ammonium chloride.The following method is recommended f o r the preparation of the solution :-Dissolve copper nitrate, the purest obtainable, in distilled water. Boil for a short time to expel t,he air, and keep at a temperature of 100" for an hour o r two in the presence of bright metallic copper in order to completely neutralise the solution. When ready for use, it should have a density of about 1.53. Add a saturated solution of ammonium chloride at about the rate of 1 drop to 100 C.C. of the nitrate. It is not easy to specify the proper amount of ammonium chloride necessary, and the surest way is to try a preliminary experiment. I f too much be present, the deposit will discolour on drying; if too little, the deposit will' oxidise in the solution.The weight of copper deposited does not appear to depend on the current density, and is practically inde- pendent of the temperature between 10" and 35'. The equivalent obtained for copper, using the nitrate, agrees very well with that calculated from the best chemical determinations. Ratio of the Specific Heats of Paraffins, &c. By J. W, CAPSTICK (Proc. Roy. Soc., 54, 101--104).-The ratio of the specific heats at constant volume and constant pressure of several gaseous paraffins and their halogen derivatives at the ordinary tempera- ture was calculated from the velocity of sound in the gases obtained by using Kundt's method. The mean values of the ratio are as fol- lows :-Methane, 1.313 ; methylic chloride, 1-279 ; methylic bromide, 1.274 ; methylic iodide, 1.286.Ethane, 1.182 ; ethylic chloride, 1.187 ; etbylic bromide, 1.188. Propane, 1.130 ; propylic chloride, 1.126 ; isopropylic chloride, 1.127 ; isopropylic bromide, 1.131. It will be noticed that these ratios fall into four groups : (a) meth- ane, ( b ) metbylic halo'ids, (c) ethane and its derivatives, ( d ) propane and its derivatives, the ratio for each group being constant. A form of vapour density apparatus, giving results concordant to. 0.1 per cent., is described in the paper. Thermal Properties of a Mixture of Carbonic Anhydride and Nitrogen. By K. TSURTJTA (Phil. Mug., [5], 36, 438--453).-The author has calculated from Andrews' observations the isothermads. isometrics, and isopiestics of a mixture of carbonic anhydride and nitrogen in the proportion of 3 to 4.He uses Clausiua' equation adopting Margules' values for the constants p = ;a - T(v + p)" R, K, a, 13. H. C J. W. RT R The results are given in tabular and curve form. J. W. Dissociation Pressure and the Individuality of Chemical Compounds. By V. KURILOFF (J. Buss. Chem.. SOC., 25, 170--192), -The author has studied the variation of the vapour pressure of ammonia with varying concentration in the liquid first obtained by Divers by passing ammonia over ammonium nitrate. The liquid behaves as if it were a solution of ammonium nitrate in ammonia,INORGANIC CHEMISTRY. 39 the vapour pressure decreasing as ammonia is removed, until the solid begins to separate out, after which it remains constant, until the whole has become solid. The solubility of the ammonium nitrate in ammonia increases with rise of temperature.Similar experiments were made with the liquid obtained by passing ammonia over ammonium bromide. The solution in this case seems to be one of the compound NHaBr,NH, in ammonia. So long its solid and liquid are present together, t.he vapour pressure again remains constant. Care must be taken, therefore, in drawing conclusions its to the individuality of substances from the constancy of their vapour pressure. This constancy may be due to the exister-ce of an indivi- dual compound, but it may also arise from the presence of a hetero- geneous mixed system. J. W. Supersaturated Solutions. By A. L. POTILITZIN (J. Russ. Clwnz. ~ o c . , 25, 201-207).-The author has stated (Abstr., 1893, ii, 509) t h a t salts containing water of crystallisation which do not decompose at the ordinary temperature in dry air or in a vacuum, or decompose only very slowly, are incapable at that temperature of forming super- saturated solutions. The hydrated salt CaS04,2H,0 is apparently an exception to this rule, as it does not lose water at the ordinary temperature, and still can give supersaturated solutions. This the author explains by assuming that the hydrate 2CaS04,Hz0, which is inore soluble than the hydrate CaSO4,2H20, exists in the solution a t the ordinary temperature, and only changes slowly into the dihydrate. Distillation in a Vacuum. By A. ANGELI (Gazzetfa, 23, ii, 104). -In the distillation of small quantities of liquid under diminished pressure, very good results are obtained by almost filling the distilla- tion flask with glass wool. J. W. W. J. P.