753

General and Physical Chemistry.

Index of Refraction of Ice. By G. MEYER (Ann. Phys. Chem. [2], 31, 321-322).-Hitherto the measurements of this index which have been made do not refer to light of any fixed wave-length. The writer therefore communicates some preliminary determinations, both for the ordinary and also the extraordinary ray, for the light from sodium, lithium, and thallium flames. C. S.

n

- 1

Refractive Index and Compressibility of Cyanogen. By J. CHAPPUIS and C. RIVIÈRE (Compt. rend., 104, 1433-1435).--This is a continuation of the authors' work on the refractive power of cyanogen at various pressures. They find that for temperatures between 0° and 30° and pressures between 1 atmos. and 4 atmos., the relation constant, holds good for this gas as for carbonic anhydride and air, and the values obtained by means of this expression differ from those given by the formula by quantities which are not greater than the errors of experiment. The numbers calculated by the first formula agree closely with the observed numbers.

d

Ny - 1

(m + 2)d

C. H. B.

Molecular Refractive Energies of Derivatives of Carbon Bisulphide. By R. NASINI and A. SOALA (Gazzetta, 17, 72-78). -Determinations are given of the refractive indices for various rays and the specific molecular refractive energies, according to the formulæ of Landolt and of Lorentz and Lorenz, of allyl sulphide and of various ethereal salts of xanthic acid. The principal results are given in the table below.

As regards these results, it is noted that in the case of allyl sulphide the found and calculated values are concordant; but in the derivatives of carbon bisulphide the values are not concordant if it is supposed that the atomic refractive energy of the sulphur-atoms is the same as

VOL. LII.

3 e

those in carbon bisulphide. If, however, it is supposed that one of the sulphur-atoms functions as in carbon bisulphide, whilst the other changes its functions and assumes that of a sulphur-atom in the sulphides or mercaptans, then the found and calculated values are concordant.

It would also appear that one of the sulphur-atoms in the dioxythiocarbonates has an atomic refractive energy of 17:42. The difference observed in other cases for the addition of the grouping CH, to the molecule is also verified for the homologous ethereal salts of xanthic acid; the isomeric diethyl and methyl propyl xanthates have not, however, identical molecular refractive energies.

V. H. V.

Molecular Refractive Energies of the Thiocyanates and Thiocarbimides. By R. NASINI and A. SCALA (Gazzetta, 17, 66-72). -In this paper a series of determinations are given of the refractive indices for various rays, and the specific molecular refractive energies of the thiocyanates and their isomerides, the thiocarbimides. The latter values are also compared with those calculated according to Brühl's data, although there remains some uncertainty as to the atomic refraction of sulphur in the thiocyanates, and of nitrogen in the cyanogen compounds generally. The following are the principal results obtained ::

It will be seen from the above results that the thiocarbimides have a greater refractive (as also dispersive) power than their isomerides; it is also shown that whereas for the first three thiocarbimides the values found for the molecular refractive energies agree with those calculated according to Brühl's data, yet for the phenyl-derivative there is a considerable difference, about 7 per cent. Further, the authors note that their results do not confirm Thomsen's hypothesis that the refractive energy and the heat of combustion are correlative quantities. V. H. V.

Dispersion in Rock-salt. By E. KETTELER (Ann. Chim. Phys. [2], 31, 322-326). The recent researches of Langley on the spectrum of radiant heat afford sufficient data for the calculation of the constants of Ketteler's dispersion formula,

n2 = — kx2 + a2 + Dλ2n/(x2 — λ3n).

By forming a table of the values of n, the accuracy of the formula is proved for a considerable range of wave-length. k in the case of rock-salt is found to be extremely small = 0.000858. If the substances for which k is known be arranged according to decreasing values of k, the order will be that of the diathermancy of the substances, rocksalt concluding the list.

The physical meaning of the term -k is, therefore, that it represents the absorption of radiant heat, and no dispersion formula wanting this term can be correct. C. S.

Red Fluorescence of Chromiferous Gallium. By L. de BOISBAUDRAN (Compt. rend., 104, 1584-1585).-The author has previously found (this vol., p. 409) that gallium oxide which contains chromium shows a red fluorescence in a vacuum. The spectrum of this fluorescence shows a very distinct line homologous with the bright lines in the spectrum of the fluorescence of chromiferous alumina and of spinel. The wave-length of this line is 16897-6898, and it rapidly diminishes in brilliancy as the substance becomes heated by the action of the discharge. The centre of the band in the spectrum of this fluorescence is at 16619; it is very nebulous at both ends, and extends through λ1080—1180 according to the intensity of the light. C. H. B.

Specific Rotation of Optically Active Substances in very Dilute Solution. By R. PRIBRAM (Ber., 20, 1840-1850).—Three explanations may be given of the influence of a solvent on the rotatory power of many active substances. 1. The molecules of the substance in solution may be aggregates of simple molecules which undergo dissociation by dilution. 2. The active substance may form hydrates of different, perhaps opposite, rotatory power, the relative quantities of which depend on the amount of water present (Bremer, Abstr., 1885, 622). 3. The solvent may alter the constitution (distance or arrangement of atoms) of the active molecules (Landolt, van t'Hoff). In the first two cases, the rotatory power might be expected to reach a limiting value when the solvent is in sufficient excess; in the last no such limit is probable.

In this third case the author gives a picture of the possible action by imagining four groups to be arranged round an unsymmetrical carbon-atom, at the solid angles of an irregular tetrahedron. A line drawn through them in the order of their magnitude represents the direction of rotation. If the plane containing groups 2 and 3 be supposed to rotate round an axis passing through the carbon-atom, and lying in the plane containing groups 1 and 4 and the carbonatom, this line will be either a right- or left-handed spiral or a plane curve. The latter position represents an inactive state of the sub

stance.

Recent improvements in the polaristrobometer by Lippich and Landolt have enabled the author to measure accurately the rotation of very dilute solutions of tartaric acid, nicotine, and cane-sugar, with the following results.

Turtaric Acid.-Arndtsen (Ann. Chim. Phys. [3], 54, 403) expresses the rotatory power at 25° by the formula [a]D=1950 +0.1393q, in

which q, the percentage of water, may vary from 50 to 95. The author gives a number of measurements of rotatory power for solutions containing from 4.7161 down to 0.3471 per cent. of acid. The value of [a] increases from 14.198° to 16-284°. The increase is thus continuous up to the highest dilution.

Nicotine. The specific rotation (left-handed) of pure nicotine, [a] = 161·55°; and Landolt (Abstr., 1878, 1) found that that of the base in solution diminishes rapidly, but irregularly, with increasing dilution. The heat developed when nicotine is mixed with water points to the formation of a hydrate, as does also the following:When water is added to a solution containing less than 20 per cent. of base, the mixture becomes turbid, and clears only on long standing. When the turbid mixture is heated to 40° it clears rapidly; but again becomes turbid on cooling or on further heating to 50°. Between 50° and 60° the turbidity amounts to milkiness, but still disappears on cooling below 50°. At 70° the nicotine separates as a layer. Furthermore, the rotation of a freshly prepared solution increases with time, and becomes constant only after 48 hours. The author finds the value of [a] to rise from 77.03° for a 40289 per cent. solution to 79-319° for a 0-8826 per cent. solution. Thus no limit has been reached.

Cane-sugar. The rotatory power has been measured by Schmitz (this Journal, 1877, ii, 876) and Tollens (ibid., 875). The latter detected a slight increase when the percentage in solution falls from 70 to 18.86, but a decrease for weaker solutions. Subsequent special experiments by Tollens (Abstr., 1884, 1285) tended to confirm this view. The author's observations show that this decrease is wellmarked and tolerably regular. In the table p = percentage of sugar, d density.

Tollens' formula, [a]D = 66-386 +0015035p - 0.0003986p2, gives results for these weak solutions differing considerably from the author's.

All the results described are at least in harmony with the third hypothesis stated above.

Сн. В.

Electric Couple with Carbon Elements. By D. TOMMASI and RADIGUET (Bull. Soc. Chim., 47, 85-88).-The positive element consists of a stick of carbon covered with a layer of lead peroxide and is contained in a canvas bag. The negative element consists of a hollow cylinder of carbon pierced with holes, into this the positive element is thrust, and the whole is placed in a glass cell which is then packed with lumps of gas carbon, and finally a concentrated solution of sodium chloride poured in until the level of the liquid is about half way up the cell. The electromotive force of this couple is from 06 to 07 volt, and no action occurs in it until the circuit is closed: it,

however, polarises rapidly, and is only suitable for intermittent work, but when thus used it lasts for an almost illimitable time, being in as good condition after two years as when first put up. The chemical action which occurs is an oxidation of the carbon at the negative pole and a reduction of the lead peroxide at the positive pole. A. P.

Nickel and Carbon Elements. By C. v. NEUMANN (Dingl. polyt. J., 264, 47).—The author has constructed a battery with nickel and carbon as galvanic elements. The exciting solution is either dilute nitric acid or aqua regia or sulphuric acid, whilst lead dioxide is the depolarising agent. The E.M.F. of this battery is said to be 0.75 volt.

D. B.

Galvanic Element. By R. EISENMANN (Dingl. polyt. J., 263, 540).—The author recommends the use of tungstic acid as an exciting agent for galvanic elements. Its action is similar to that of chromic acid but it has the advantage of being rapidly oxidised after reduction, whilst the addition of a small amount of phosphoric acid suffices to keep the tungstates in solution in the acid liquid.

D. B.

Polarisation of Copper by the Extension of the Surface in Contact with a Liquid Conductor. By KROUCHKOLL (Compt. rend., 104, 1436—1437).-A spiral of copper immersed in water or in water containing 2 per cent. of sodium sulphate becomes negative at the moment when the surface in contact with the liquid is increased. With a certain degree of polarisation, the phenomenon is reversed, and the copper becomes positive with extension of surface, and with an intermediate degree of polarisation variations in the surface of the metal in contact with the liquid have no effect on the electromotive force. C. H. B.

Conductivity of Amalgams. By C. L. WEBER (Ann. Phys. Chim. [2], 243-250).—Experiments were made with amalgams of mercury with each of the following metals: tin, bismuth, lead, cadmium. The measurements being made at high temperatures, so as to secure a homogeneous conductor. The resistance of the amalgam contained in a U-tube was found by the method given by Thomson for the determination of small resistances. The electrodes were of iron on account of corrosion. To avoid the influence of thermoelectric effects, the mean of the resistances with the direct and reversed current was taken. An india-rubber tube was attached to the arm of the U-tube, and by suction and compression the amalgam was kept well mixed.

Taking as ordinate the specific resistance and as abscissa the percentage of metal in the amalgam, curves are traced showing the variation of the specific resistance with the composition of the amalgam. All the curves concur in showing that the effect of adding a small quantity of metal to the mercury is to cause a rapid decrease of resistance, and that the conductivity of the amalgam is not the mean conductivity of its constituents. In other respects the amalgams separate into two groups, those of like atomic weight going together. In the tin and cadmium amalgams the resistance, although falling rapidly at