« PreviousContinue »
General and Physical Chemistry.
Dispersion Equivalents. By J. H. GLADSTONE (Proc. Roy. Soc., 42, 401-410).—This paper is a continuation of the author's researches on dispersion equivalents. Notwithstanding the difficulties of the investigation, the following conclusions have been arrived at:1. That dispersion, like refraction, is primarily a question of atomic constitution. 2. That dispersion, like refraction, is modified by profound differences of constitution, such as change of atomicity. 3. That dispersion frequently reveals differences of constitution, at present unrecognised. The following dispersion equivalents (H-A) have been determined:-Phosphorus (liquid), 30; sulphur (double bond), 26; sulphur (single bonds), 12; hydrogen, 004; carbon, 0.26, 0.51, and 0.66; oxygen (double bond), 0.18; oxygen (single bonds), 0.10; chlorine, 050; bromine, 122; iodine, 365; nitrogen, 0.10; CH2, 034; NO2, 0.82. The values for CH2, H, and C are worked out in the same way as the refraction equivalents. In unsaturated compounds, the dispersion equivalent is much greater, (0.5) in allyl compounds and olefines, and at least 0.8 in the aromatic series. Where the carbon has all four bands satisfied with carbon-atoms (with refraction value 60), the dispersion equivalent is enormously increased. In considering the dispersion equivalents of solutions of metallic salts, it is pointed out that where the solution is dilute the values are untrustworthy, owing to the smallness of the specific dispersion, the values for potassium and sodium alone are therefore considered. The difference between the dispersion equivalents of their salts is 0·09. In determining the value for potassium itself, the haloïd salt was rejected, as it was anticipated that the chlorine value might be higher than it is in organic compounds, as is the case with the refraction equivalents. Determined from the formate and acetate, with the values given above for carbon, hydrogen, and oxygen, the dispersion equivalent for potassium is 0.53 and 0.44 for the salts respectively. From potassium hydroxide viewed as water, with a hydrogen-atom replaced, the value 0.565 is obtained. From the nitrite, by subtracting the value for NO2, 048 is obtained. From the cyanide, 058; from the carbonate, 040; from the oxalate, 0:59. These variations cannot be due to experimental error, nor is it probable that potassium has more than one dispersion equivalent, as it has only one refraction equivalent. The uncertainty probably lies in the value of the radicles to which the metal is joined.
H. K. T.
Mathematical Analysis of the Spectra of Magnesium and Carbon. By A. GRUNWALD (Monatsh., 8, 650-712).-In accordance with the principle laid down by the author (Abstr., 1887, 1070), an analysis of the spectra of magnesium and carbon has been effected, the data of different observers, chiefly those of Liveing and Dewar, being used for this purpose.
The magnesium spectrum is found to show the presence of the primary substance c in the same condition in which it is found in oxygen and carbon, of the primary substance b in the state in which it exists in free hydrogen, and in the more condensed state in which it is found in the water-vapour spectrum, and also of b (helium) in an uncondensed state. Besides these, a number of very weak, and at present unknown hydrogen and oxygen lines are present.
The spectrum of carbon contains the primary substance c in the state in which it is found in oxygen and magnesium, and also the substance b. This latter exists in four different conditions: in the state in which it is observed in free hydrogen; in the state in which it exists in the hydrogen of water-vapour; and in a more dilated chemical condition, and a more condensed condition than that in which it occurs in free hydrogen. A number of hydrogen and oxygen lines are also present, most of them very weak, but which, on multiplying their wave-lengths by the factor, as in the case of those in the magnesium spectrum also, are converted into lines in the water spectrum. H. C.
Compounds of the Rare Earths yielding Absorptionspectra. By G. KRÜSS and L. NILSON (Ber., 21, 585-588).—A rejoinder to Bailey (this vol., p. 208).
Contact Electricity. By W. v. ULJANIN (Ann. Phys. Chem. , 33, 238). The author points out that Exner (this vol., p. 208) has misunderstood his method (Ann. Phys. Chem. , 30, 699) of determining the potential difference between zinc and copper, as he appears to have assumed that the author covered a copper cylinder with a zinc one, and inserted such a fraction of a Daniell, that when the latter cylinder was removed there was no deflection of the electrometer. This arrangement would clearly not enable the potential difference to be measured, as it would require that the envelope also should be at the same potential, and the latter is determined by that of the walls of the room.
In the arrangement used, the two cylinders were of zinc, and were surrounded by a copper envelope, and before removing the outer cylinder it was separated from the inner one. Then assuming the two zinc cylinders to be at the same potential, there would be no deflection if the copper envelope was at the same potential. This condition was satisfied by the introduction of a certain fraction of a Daniell in the earth connection of the envelope.
It is clear that the method would not serve to determine any potential difference between the zinc cylinders, as it depends on the assumption that they are at the same potential, being of the same metal, and in contact. G. W. T.
Maximum Galvanic Polarisation of Platinum Electrodes in Sulphuric Acid. By C. FROMME (Ann. Phys. Chem. , 33, 80128). The great discrepancies between the different determinations of the maximum polarisation in a voltameter containing dilute sulphuric acid with platinum electrodes, induced the author to investigate
the circumstances on which the amount of polarisation depends. A priori, the polarisation might be expected to depend on the nature of the surface of the electrodes, on their dimensions, on the concentration of the acid, and on the pressure at which the gases are liberated.
The concentration of the acid in the different experiments varied from 0.18 to 65 per cent.
The author finds that the manner in which the amount of polarisation varies with the concentration is most complicated in the case of very dilute solutions, for, as the concentration is gradually increased, the polarisation at first increases and reaches a maximum, and afterwards falls to a minimum; when the anode is small, it passes through a second maximum and minimum, until it finally increases steadily with the concentration; with a larger anode, only a single maximum and minimum are observed.
In very dilute solutions, the amount of polarisation is found to depend on whether the water used is distilled in glass or in metallic vessels, this being doubtless due to the presence of small particles of glass or of metal in the distilled water.
When the cathode is small, its surface becomes blackened by the passage of the current, whilst a larger cathode is not sensibly altered. With the more dilute solutions, and when both the electrodes were small, a yellow deposit was observed on the anode. The black deposit remains unaltered after treatment with concentrated sulphuric acid, but it is slowly dissolved by aqua regia. It can also be removed by reversing the current for some time, or it can be scraped off. This deposit had already been observed by de la Rive (Ann. Phys. Chem., 41, 156; 45, 421) and by Poggendorff (ibid., 61, 605), and their experiments showed that it consisted of platinum in a state of powder, mechanically detached from the cathode. In some of the experiments, even when the cathode is larger, a greyish-brown deposit was observed on the latter, but only when the water had been distilled in glass vessels, from which the author concludes that it was due to particles of glass. It was easily dissolved by concentrated sulphuric acid.
In the case of the larger anodes, a dark yellow coloration was observed after some time. This yellow deposit on the anodes was unaffected by treatment with hot concentrated sulphuric scid or aqua regia, and it occurred whether the water had been distilled in glass or in metallic vessels. The author was unable to determine its cause, but concluded that it was not due to the presence of any impurity in the solution. The amount of polarisation is found to depend on the size of the electrodes; with dilute solutions, the size of the anode is the more important, with stronger ones that of the cathode.
With the solutions used containing, as previously stated, from 0.18 to 65 per cent. of acid, the E.M.F. of polarisation varied from 1.94 to 2:43 of a Daniell when the cathode and anode were both large; from 1:45 to 2.98 when the cathode was small and the anode large; from 1.90 to 418 when both cathode and anode were small; and from 1.89 to 4:31 when the cathode was large and the anode small. The least variation, therefore, occurs when both the electrodes are large, and the greatest when the cathode is large and the anode small.
The resistance of the voltameter when traversed by a strong steady
current diminishes as the concentration of the acid increases, and ultimately reaches a minimum value when the concentration is about the same as that for which the conductivity is found to be a maximum by observations with alternate currents; after this, it increases with further increase in the concentration. When, however, the anode is small, the resistance continues to diminish up to the highest limits of concentration used in the experiments. G. W. T.
Electromotive Forces of Metals in Cyanide Solutions. By S. P. THOMPSON (Proc. Roy. Soc., 42, 387-389).-The electromotive forces of copper and zinc in cyanide solutions are examined in order to ascertain the cause of the possibility of depositing these two metals simultaneously. It is found that with higher concentration, the E.M.F. of copper increases more than that of zinc; moreover, in a cold dilute solution of potassic cyanide the E.M.F. of zinc is higher than that of copper, whilst in a boiling saturated solution the E.M.F. of copper is greater than that of zinc: hence it is possible to construct a battery consisting of one metal, copper, and one electrolyte, a solution of potassic cyanide, the anode being kept hot and the cathode cold. Tables are given showing the E.M.F.'s of various metals compared with carbon in cyanide solutions of various strengths. Maxima are frequently found at intermediate stages of concentration. In a mixed solution of copper and zinc cyanides, there is a neutral condition, in which the E.M.F.'s of zinc and copper are equal, depending on the relative amounts of metal, the concentration of the solution, and the temperature. The E.M.F. of the copper is the most sensitive, especially to variations in the concentration of the solution. At the cathode, the concentration is determined, on the one hand, by the rapidity with which the metal is deposited, that is, by the currentdensity; on the other, by the rapidity of diffusion; hence there will be a certain current-density at which the solution will be maintained in the neutral condition and the metals be deposited equally.
H. K. T.
Resolution of the Electromotive Forces of Galvanic Elements. By J. MIESLER (Monatsh., 8, 713-720).—In continuation of his work on this subject (this vol., p. 330), the author has examined Marié- Davy, de la Rue, and Niaudet cells, and in each the sum of the potential differences in the various parts of the cell is found to be equal to the total E.M.F. Accumulators were examined, and for these the above was also found to be true. On discharging an accumulator and measuring the potential differences at different intervals, as the total E.M.F. decreased to about one-half of its original value, the potential difference between the negative plate and acid also diminished, but that between the positive plate and acid remained the After the cell had been short circuited for some time, the exact opposite had, however, taken place, for the potential difference between the negative plate and acid was still the same, whilst that between the positive plate and acid had decreased. An attempt mechanically to construct an accumulator that should give the same potential differences as a charged accumulator failed.
Thermal Alteration in a Daniell Cell and in an Accumulator. By G. MEYER (Ann. Phys. Chem. , 33, 265–289).— Investigations have been made on the thermal changes in a Daniell cell by Lindig (Ann. Phys. Chem., 123, 1), Voller (ibid., 149, 394), and v. Helmholtz (Ber., 18, 22), and the latter has shown that in a zinc sulphate cell the temperature-coefficient depends on the degree of concentration of the solution. The object of this paper is to determine more fully on what circumstances the temperature-coefficient depends, in the case both of sulphuric and zinc sulphate cells, and to determine whether the temperature-coefficient of the cell is equal to the sum of the temperature-coefficients at each contact of unlike substances.
In order to ensure their purity, the metals used were obtained by electrolytic deposition from copper sulphate and zinc sulphate, and the copper sulphate, zinc sulphate, and sulphuric acid were chemically pure. The metals and liquids composing the cell were contained in a glass tube of special construction, and the liquids were separated by parchment-paper; the dissolved air being got rid of by use of an air-pump. The measurements of the E.M.F. were always made with a quadrant electrometer, so that there was no polarisation, and the electrometer reading was taken directly after the zinc was introduced into the liquid, to prevent a coating of hydrogen being formed, at the higher temperatures, by the action of the sulphuric acid on the amalgamated zinc. The results obtained with the cells were as follows:-The E.M.F. of a Daniell cell with sulphuric acid increases with the temperature, and the value of the temperature-coefficient depends on the degree of concentration of the liquids in the cell, increasing with an increase in the concentration of the sulphuric acid, until the solution contains about 30 per cent. of the acid, when it attains a maximum value, and diminishes when the concentration is increased beyond this point. The temperature-coefficient increases continuously without attaining a maximum as the concentration of the copper sulphate is increased.
In the case of a zinc sulphate cell, the E.M.F. diminishes as the temperature rises, and when the concentration of the zinc sulphate is increased from a low degree the temperature-coefficient falls to zero, and as the concentration is further increased this has a continually increasing negative value. The effect on the temperature-coefficient of varying the concentration of the copper sulphate solution is the same as in the case of the sulphuric acid cell.
In the accumulator, the temperature-coefficient was found to increase with increased concentration of the sulphuric acid, but the author has not yet been able to determine whether the degree of concentration has any effect on the E.M.F., as the latter begins to diminish as soon as the charging current is discontinued, at first rapidly, and then slowly, but not slowly enough to enable any conclusions to be drawn from the measurements of E.M.F., each of which occupied about six minutes.
During the experiments on the accumulator, whilst evolution of gas was observed from the lead plates when it was placed under the airpump to free the sulphuric acid from dissolved air, it was found