and similar cases were found to be unaltered by the decrease in the electrolytic dissociation. The author concludes that for the salts examined, that is, copper sulphate and nitrate, nickel sulphate, and potassium permanganate, the colour of the aqueous solution is independent of the electrolytic dissociation. W. J. P.

Molecular Dissymmetry. By P. A GUYE (Chem. Centr., 1892, i, 10; from Arch. sci. phys. nat. Geneva [3], 26, 333-369).—In addition to the examples which the author has already given (this vol., p. 399) in proof of the correctness of the symmetrical and unsymmetrical arrangement of the groups of atoms in relation to the carbon atom, he now names derivatives of tartaric, malonic, aspartic, lactic, and malic acids, of leucine, and phenyl mercaptan. Exceptions occur in the case of glutamic acid, the constitution of which is not certain, and in those of some asymmetrical compounds the groups of which have approximately equal masses.

J. W. L.

Stereochemistry of Diacetyltartaric Acid. By A. COLSON (Compt. rend., 114, 175-178).-Diacetyltartaric acid has been obtained by the author in the crystalline form, with 3 mols. H2O. It fuses at 58°, is very deliquescent and soluble in water, alcohol, and ether, less soluble in benzene. In these four solvents it rotates the plane of polarisation to the left, although it is derived from dextrorotatory tartaric acid. Its salts are lavorotatory in aqueous

solution.

It may be obtained in the crystalline form :-(1) By allowing diacetyltartaric anhydride to deliquesce, taking up with dry ether, and slowly evaporating in dry air. By this means rhomboidal, almost square, tables are obtained. (2) By treating the anhydride with ether saturated with water, and slowly evaporating the ether.

The conversion of the dextrorotatory tartaric acid into a lavorotatory compound is not due to the heat evolved during the formation of the latter, for dextrorotatory tartaric acid is regenerated by slow hydrolysis through the action of the moisture of the air. The optical inversion is due to the action of the inactive acetic acid. It is concluded that an inactive substance such as water may affect the rotatory power, but the tetrahedron formula fails to indicate this. The tetravalency of carbon, founded on the Le Bel-Van't Hoff notation, excludes also molecular combinations such as the crystallised acid described.

According to Guye's method of accounting for diacetyltartaric acid being lævorotatory, on the assumption of the tetrahedron formula the diacetyltartrates should be dextrorotatory, whereas they are lævorotatory. According to Guye, diacetyltartaric anhydride should be more strongly lavorotatory than the acid; on the contrary, it is dextrorotatory.

The conclusion is therefore drawn that the chemical notation based on the properties of the regular tetrahedron is insufficient to represent the constitution of active substances, and may lead to inaccurate predictions.

W. T.

Stereochemistry and the Laws of Rotatory Power. By P. A. GUYE (Compt. rend., 114, 473-476).-A reply to some objections recently brought by Colson (preceding abstract) against the author's method of calculating the sign of the rotatory power of carbon compounds. The method was not intended to be applied to ring compounds, on account of the uncertainty as to the amount of deformation of the angles of the tetrahedra in the molecules of such compounds. As the particular compound, diacety'tartaric anhydride, which Colson selects in illustration of his argument, is a ring compound, his conclusions are necessarily invalid.

JN. W.

The

Coexistence of Dielectric Power and Electrolytic Conductivity. By E. BOUTY (Compt. rend., 114, 533-535).-The measurements were made by the method previously employed to determine the dielectric constant of mica at high temperatures. The dielectric constant for pure terebenthene was found to be 2.25, which is exactly the mean of the determinations of Silow, Quincke, Palaz, and Negreano. The conductivity of distilled water is so great that the measurements of time cannot be made with sufficient accuracy. determination of the dielectric constant of ice, however, presents no great difficulty, and the value of the constant is found to be 78 at -23°. As the temperature rises, the conductivity increases rapidly, but the dielectric constant shows no appreciable variation. The constant remains the same even if a small quantity of sodium chloride is added to the water before freezing, or if river water is used instead of distilled water. It follows that dielectric power and electrolytic conductivity may coexist in the same substance, the former remaining practically constant, whilst the latter varies within wide limits.

C. H. B.

Galvanic Polarisation at Small Electrodes. By K. R. KOCH and A. WÜLLNER (Ann. Phys. Chem. [2], 45, 475-507; 759-797). -Fromme found that with great current density strong polarisation appeared at small electrodes (Abstr., 1890, 316, 675). Richarz, on the other hand, concluded that the polarisation does not alter with the current density, but that the resistance in the electrolyte does. (Abstr., 1890, 676). The authors have investigated the question afresh, using a new method of measurement. They observed simultaneously the current strength, the difference of potential of the electrodes, and also, by an electrometric method, the polarisation at each electrode. From the data, the resistance of the electrolytic cell could be calculated. Their results with solutions of sulphuric acid of various strengths, and with electrodes of different sizes and shapes, are given in numerous tables.

In the second portion of their paper, the authors give an account of their investigations on the phenomena of "current reversal" (sudden reduction of the direct current and increase of polarisation), produced by increasing the current strength beyond a certain limit. The results obtained with various solutions and electrodes are given in tabular form; and figures, after instantaneous photographs, show the evolution of gas, &c., at the electrodes, with the current below and above the limit for reversal.

The authors state the conclusions at which they have arrived, as follows:

1. There is, at short electrodes of platinum wire in dilute sulphuric acid, a polarisation which increases considerably with the current strength.

2. This polarisation is due to an electromotive force opposed to that of the direct current, and to the resistance of a badly conducting layer which is formed round the electrodes. The electromotive force of polarisation is not dependent on the length of the wire electrodes, or, in general, on the concentration of the solution; and has the value to which the polarisation of large electrodes approximates with increasing current density, namely, 3.79 volts.

3. The resistance of the transitional layer is independent of the current strength with a given electrode and a given solution. For the same pair of electrodes it is proportional to the specific resistance of the solution; and for the same solution it diminishes as the length of the wire electrodes increases.

4. These rules are only valid for current strengths below a certain limit, which depends on the length of the electrodes and on the conductivity of the solution. When this limit is reached, an increase of the electromotive force causes a "reversal"; by the sudden increase of polarisation at the smaller electrode, the current becomes very weak. The strength of the residual current is not increased by an augmentation of the electromotive force, and is greater for long than for short wire electrodes.

5. If the reversal is caused by the great polarisation at the anode, this electrode becomes incandescent, sometimes splits, and is rapidly destroyed. If the seat of the reversal is at the cathode, a bluishwhite glow, due to a gaseous envelope, surrounds this electrode, which may itself become incandescent. It is, however, not destroyed.

6. Zinc electrodes in zinc sulphate solution and copper electrodes in cupric sulphate solution exhibit, likewise, a polarisation which increases with the current strength. At a certain current strength a sudden increase of the polarisation at the anode take place; and this great polarisation can be obtained at large anodes with small current density by producing it first at a small portion of the surface by means of a large current density.

J. W.

Electro-capillary Phenomena. By Gour (Compt. rend., 114, 211-214).—If a dilute solution of sulphuric acid is taken, and with the capillary electrometer the law determined which connects the height of the mercurial column with the polarisation of the meniscus, on taking the polarisations as abscisse and the heights as ordinates, the well-known parabolic curve of Lippmann is obtained. If iodide of potassium is substituted for sulphuric acid, the maximum is found. to be less, and the portion of the curve during which the capillary meniscus plays the part of the anode, or the anodic portion, is steeper in the case of the sulphuric acid, or, in other words, the electrometer is more sensitive with this liquid. It follows from this that the two curves cannot be made to coincide by moving them along the axis of abscissæ, but by this means it is found that their cathodic portions

can be made to coincide at a short distance below the maximum. The same is true of other potassium salts besides the iodide. The reason for this is very evident. On the anodic side, the surface tension will depend on the nature of the mercury compound, oxide, iodide, &c., which tends to form, but at the cathode, hydrogen alone is liberated in the above cases. H. C.

Optical Measurement of High Temperatures. By H. LE CHATELIER (Compt. rend., 114, 214-216).-The author recommends for the measurement of high temperatures, the photometric determination of the light emitted from a substance at the temperature under observation. The principal difficulties are, that the intensity of the radiation from such a substance depends not only on its temperature but also on its chemical nature, the physical condition of its surface, and the temperature of the substances which surround it. In cases where its diffusive power is nothing, the radiation is independent of the temperature of its surroundings, and depends only on its own temperature. This is the case with the magnetic oxide of iron, and carbon. The emissive power of other substances may be checked, as the author shows, by reference to these two, and scales constructed by means of which high temperatures can be measured by determining the light emitted from different incandescent sub

stances.

H. C.

Optical Measurement of High Temperatures. By H. BECQUEREL (Compt. rend., 114, 255-257)-Observations on a paper by Le Chatelier, dealing with the same subject (see preceding abstract). The author points out that the principle of the method recommended by Le Chatelier for the measurement of high temperatures is one which was put forward and fully explained by his father in 1862 (Ann. Chim. Phys. [3], 68). H. C.

Specific Heat of the Diamond. By C. E. CARBONELLI (Gazzetta, 22, i, 123–130).—The author points out that the non-metallic elements in the seventh, sixth, and fifth groups of the Mendeléeff classification possess the general property of existing in the gaseous state in molecules containing two, three, and four atoms respectively. He considers that this periodicity may extend to the fourth group, which contains carbon, so that the gaseous molecules of elements in this group would contain five atoms. If this pentatomic molecule be supposed to preserve its individuality in the solid state the atomic heat of carbon must be multiplied by 5 to give the constant (6·4) of Dulong and Petit's law. The product of the specific heat of the diamond and the atomic weight of carbon is 1.25. On multiplying this by 5 a number (6.25) is obtained which accords with that required by Dulong and Petit's law. W. J. P.

Measurement of the Specific Heat of Liquids at Temperatures above their Boiling Points under Ordinary Pressure. By G. P. GRIMALDI (Real. Accad. Linc., 7, ii, 58–63).—All the determinations of the specific heat of liquids at temperatures above

their boiling points under ordinary pressure have been hitherto made by the method of cooling, and the results obtained are very inconsistent. The author has devised an apparatus for making these measurements by the method of mixtures.

The liquid to be experimented on is contained in a steel cylinder A, whose sides are 3 mm. thick and whose volume is about 170 c.c. The cover communicates by means of a worm with another strong steel vessel B, in order to allow for the expansion of the liquid. When this whole arrangement has been raised to the required temperature in suitably heated jackets, the cylinder A is transferred to the calorimeter and the necessary thermometric measurements are made. The calorimeter, which has a capacity of about 5 litres, is made of very light polished brass, and contains petroleum, boiling above 300°, as the cooling liquid.

The specific heat of a cylinder of zinc is subsequently measured in the same apparatus, such a weight of metal being taken as to give approximately the same thermometric data as were obtained with the cylinder containing the liquid. From the two sets of measurements thus obtained, the specific heat of the liquid can be calculated. The results are satisfactory.

W. J. P.

Heats of Combination of Bromine and Iodine with Magnesium. By N. BEKETOFF (Chem. Centr., 1892, i, 11; from Bull. Acad. St. Pétersbourg [2], 34, 291-292).-The author has determined the heats of solution of magnesium bromide and iodide. He takes Thomsen's determinations of the heat of combination of iodine and bromine with magnesium in solution; the difference being the heats of combination of the metal with the halogens. The results are: for magnesium bromide, 165000 - 43300 = 121700 cal., and for magnesium iodide, 13460049800 84800 cal. Thus the combining heats of these halogens with magnesium are less than that of the oxide (140000 cal.) and the author suggests that it is another proof that the nearer the masses of two elements approximate to one another, the greater is the energy displayed in their combination. He prepared the anhydrous salts by means of Lerch's method-the direct combination of the halogen with excess of magnesium, in sealed tubes.

J. W. L.

Heat of Formation of Potassium Tricarballylates. By G. MASSOL (Compt. rend., 114, 487-489).-The heat of solution of tricarballylic acid, melting at 163° (1 mol. in 6 litres of water) is -6.55 Cal. The heat of neutralisation with potash is +27-22, +24.94, and +19.58 Cal. for the first, second, and third acid radicles respectively (all substances calculated as solid).

Monopotassium tricarballylate, CH,O,K+ 2H2O, as obtained by evaporating the solution to dryness, is a hard, white, non-deliquescent mass. It loses the first molecule of water of crystallisation at 120°, and the second at 140°. Dipotassium tricarballylate crystallises in rhombic plates, and loses its water of crystallisation at 100.°. Tripotassium carballylate is obtained in a similar way as a syrupy mass.