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Lead sulphate, nearly white. In the phosphoroscope, red and orange are cut off.

Magnesia, pink; 5 per cent. with lime greenish, turning red as the powder heats.

Potassium with lime, bright. Residual glow persistent.
Samarium (see Phil. Trans., 1885, 709).

Scandium as earth or sulphate, very faint blue.

Sodium sulphate gives a greenish tinge to the phosphorescence of calcium sulphate. The sodium line is visible in the spectrum.

Strontia, rich blue with continuous spectrum. In the phosphoroscope, the glow is bright green, the red and blue ends being cut off.

Thorium, as oxide or sulphate, alone or with lime, does not phos. phoresce at all, and the tube rapidly becomes non-conducting, the spark passing across the gauge (37 mm. in air) rather than through the tube; in the same vacuum, when yttria takes the place of thoria, a spark of 7 mm. length in air will pass through the tube. This phenomenon is inexplicable; evidently the passage of electricity through the tube depends mainly on the phosphorogenic properties of the earth opposite the poles.

Thulium and erbinm together phosphoresce green (Proc. Roy. Soc., 40, 77). The spectrum shows a faint blue double line, which is intensified by the presence of lime. Some of the yttrium lines are also

seen.

Ytterbium when pure gives blue phosphorescence without bands. Some specimens, not quite pure, give bands in the blue which are intensified by the addition of lime, and which the author has carefully measured. Their origin is still uncertain.

The higher fractions of yttria sometimes show a sharp green line (1/2 325 approximately). These fractions phosphoresce of a goldenyellow colour, the fractions at the other end phosphorescing yellowishgreen. The green line may possibly belong to a new earth.

The phosphorescence of various mixtures of oxides with yttria (usually as sulphates) is then described. Most earths have the effect of destroying, or diminishing the brilliancy of the yttric phosphorescence. Yttria (5 per cent.) with alumina gives a good yttrium spectrum. In the phosphoroscope, the lines GB and Ga first appear together, then Go. 0.5 per cent. of bismuth with yttria then suppresses the citron line Go, thereby rendering visible the samarium double green line and GB. With larger proportions of bismuth, the spectrum either is that of yttrium, or is bad. Cerium and didymium tend to deaden the yttrium spectrum. With zinc (95 per cent.), the phosphorescence is yellowish-white and brilliant. In the phosphoroscope, the colour becomes reddish and the line GB appears first. Go is suppressed. If samarium is present, its spectrum now comes out distinctly.

Zinc sulphide (Sidot's hexagonal blende, Compt. rend., 62, 999, and 63, 188) phosphoresces most brilliantly even in a vacuum of several inches. The glow is then green; but as the exhaustion proceeds it becomes blue at the edges of the crystals. At a high exhaustion, the two colours are of equal brightness, but in the phos

phoroscope the blue is only seen at a high speed. The green glow lasts for an hour or more.

The author then reviews the evidence on which he bases the claims of the bodies Ga, GB, &c., to be regarded as separate entities, and the influence of baryta, strontia, and lime is discussed at length in each case. It is remarkable that the spark spectra of old yttrium, and of the higher and lower fractions obtained from it, are perfectly identical, although the phosphorescent spectra and chemical properties of the three are markedly different. Two theories of the true nature of these substances are suggested, namely, the hypothesis of sub-molecules which differ from each other "according to the position they occupy in the yttrium edifice," and the hypothesis that each of them is an independent element. On the latter view, the spark spectrum of yttrium may be supposed to belong to Go, which is nowhere completely separated during the process of fractionation. A third view is that of de Boisbaudran, who considers that yttrium is an element giving a spark spectrum, but not phosphorescing in a vacuum; and that the phosphorescent spectra are due to impurities; these are two in number, and are provisionally named Zx and Zẞ.

CH. B.

All

Sharp Line Spectrum of Phosphorescent Alumina. By W. CROOKES (Chem. News, 56, 59—62, 72–74).-A rejoinder to Boisbaudran (this vol., pp. 191, 409, 538, 625, 755). The author has proved by direct experiment the possibility of removing very minute proportions of chromium from large quantities of alumina:-1. By boiling the alkaline solution; 2. By passing chlorine through the alkaline solution; 3. By fractional crystallisation of ammonia alum. these methods were employed in the preparation of the author's "high alumina," in which not the slightest indication of chromium could be detected, nevertheless a sharp line phosphorescent spectrum was obtained, including the red line; hence proving that alumina without chromium can produce it. Next the author shows that chromium in admixture with glucina, magnesia, lime, zinc oxide and other similar substances, and subjected to heating with and without sulphuric acid, and to temperatures varying from cherry-red to full white, did not show any sharp red line. "The general character of the phosphorescence was reddish-orange, the spectrum being almost continuous, with the extreme red and blue ends obliterated." Hence chromium in many solid solvents does not appear to give the sharp red line spectrum. Moreover, Boisbaudran's chromium-gallium red line has a wave-length 16897 to 6898 (= 2102), very far from tl e

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alumina red line 16940 or 2076; besides owing to the chemical analogy of aluminium and gallium, it is quite natural to expect a resemblance in their spectra.

In connection with alumina and samaria (Boisbaudran, this vol., p. 1008), it is shown that alum may be obtained quite free from samaria by fractional crystallisation; hence the author's high alumina is free from this impurity. And he finds that the mixed sulphates of

aluminium and samarium heated to redness give the phosphorescent spectrum of the latter modified by the presence of the former, which is explained in this way: a red heat is not sufficient to decompose the sulphates, and samarium sulphate is phosphorescent, whereas aluminium sulphate is not. On the other hand, when the sulphate mixture is heated at a very high temperature, both are decomposed, and the residue of alumina and samaria gives the new sharp line spectrum of alumina, which might be expected, since samaria alone gives practically no phosphorescent spectrum. Maps and detailed descriptions of the spectra are given in the paper. D. A. L.

Sharp Line Spectra of Phosphorescent Yttria and Lanthana. By W. CROOKES (Chem. News, 56, 62, 81-82).-Yttria precipitated from the sulphate by ammonia, and heated to redness, does not phosphoresce; but when ignited at a full white heat, it phosphoresces with a clear yellow light, and gives a spectrum containing sharp lines:1 from 224 to 370 these are numerous and in many cases sharp lines;

λ

then follows a clear space, and from

12

409 to 500 some nebulous groups.

A specimen of lanthana, treated in a similar manner, phosphoresced of a superficial yellow colour, and gave a very brilliant spectrum. A line at

1

x2 224, groups of bands from 237 to 285, a band at about 330 and 383, and 407. Maps, tables, and descriptions of both the spectra are furnished in the papers. At present no striking results have been obtained by treating in the same manner niobic acid, samaria, ytterbia, and erbia.

D. A. L.

Chemical Structure of Oxygen and Hydrogen, and their Dissociation in the Sun's Atmosphere. By A. GUNWALD (Phil. Mag. [5], 24, 354-367).—Let [a] be the volume of a primary element in a gaseous substance A, and let [a'] be the volume which the element occupies when A has combined with another gas, then the wave-lengths of the rays which the element emits in its first combination are to the wave-lengths which it emits in its second combination, as a [a] [a']. Thus, whilst HCl, HBr, and HI give spectra consisting of hydrogen and halogen lines only, H2O gives a spectrum which may be obtained by multiplying the second hydrogen spectrum by. By this means, water lines hitherto unnoticed have been detected. Further the wave-lengths of the hydrogen spectrum can be divided into two groups, (a) and (b), such that (a) × 18 and (b) give lines in the water-spectrum; hence by the preceding reasoning hydrogen consists of two elements, a and b. Let [a] and [b] be the volumes which they occupy in a unit volume of hydrogen, then [a] + [b]= 1, moreover 18 [a] + ÷ [b] = ÷ ; . '. [a] : [b] = 4 : 1, or hydrogen consists of 4 vols. of the element a combined with 1 vol. of the element b. Spectra are given for the elements a and b. In accordance with the above principle, the wave-lengths of oxygen and hydrogen multiplied by give the water-spectrum. In the same

way, the oxygen spectrum may be split up into sets of lines, which when multiplied by suitable factors give lines in the compound H spectrum and water-spectrum, and from these factors the formula 0 = H' [b1(bics)s] is obtained, or oxygen is composed of the modified hydrogen H', which radiates the compound line spectrum of hydrogen, of the element b, and of a new element c. The composition of carbon and nitrogen is also investigated. By a comparison of the a and b spectra with the chromospheric lines, it is found that hydrogen exists in a dissociated state in the sun's atmosphere, and that the element b is identical with helium D3 5874-9, whilst the extremely light element a forms the corona substance λ = 5315·9, and is named by the author coronium. H. K. T.

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Photochromatic Properties of Silver Chloride. By G. STAATS (Ber., 20, 2322-2323).-When a well-polished plate of silver is dipped into a 5 per cent. solution of iron chloride, it acquires a slate colour. The plate is taken out of the solution after 10 seconds, dried quickly (without heating), and covered with red, emerald, orange, and cornflower-blue glass. In sunshine, the colours appear on the plate after a few minutes; over-exposed plates, especially blue ones, are brownish. The colours dissolve readily in aqueous ammonia. If the plate is heated before exposure, it acquires first a violet and then a red colour, and at the same time partly loses its sensitiveness to yellow and green light. The experiment is suggested as suitable for a lecture experiment.

N. H. M.

Modification of the Ferric Chloride Cell. By T. MOORE (Chem. News, 56, 64).—Potassium chlorate, hydrochloric acid, and a very small quantity of bromine are recommended in place of bromine alone (Warren, this vol., p. 413), as more economical and equally efficient for the regeneration of the ferric chloride in ferric chloride cells. Cells composed of zinc and carbon immersed in a strong solution of potassium permanganate and ammonium chloride are suggested for use in batteries for electric bells, &c. Exhausted Leclanché cells can be to a great extent revived by pouring a warm, strong, and slightly acid solution of permanganate into the porous cell.

D. A. L.

Electrical Conductivity of Hot Gases. By J. BUCHANAN (Phil. Mag. [5], 24, 297-302).—In these experiments, small pieces of platinum foil are placed vertically and parallel with a flat gas-flame between them, the platinum discs being connected with the binding screws of a condenser charged from a Leclanché battery, and with the quadrants of an electrometer; one pair of quadrants being connected to earth. The flame being in action, the battery was disconnected, and scalereadings taken at equal intervals of time until zero was nearly reached. From these readings the rate of leakage could be found.

Curves are plotted in which the scale-readings of the electrometer are the ordinates, and the times the abscissæ, and equations are obtained. It was found that the rate of leakage was more rapid when the insulated quadrant was negatively charged than when positive.

H. K. T.

Electromotive Dilution Constants of Silver and Copper Salts. By J. MIESLER (Monatsh. Chem., 8, 193-196).-Moser (Abstr., 1886, 925) has applied the term electromotive dilution constant to the electromotive force of the current between two solutions of single and double concentration. The values of the constants determined by the present series of experiments are given in the following table:Nitrate.

Copper

Lead

Zinc

Silver

Acetate.
2.3

Sulphate.
3.6

[blocks in formation]

Thermochemical Law conjectured by Pebal respecting Nonreversible Electrolytic Actions. By L. BOLTZMAMM (Monatsh. Chem., 8, 230-236).-The present paper has been constructed from a few data in the papers left by Pebal, and from some suggestions made to Boltzmann a few days before Pebal's death.

If a current is produced through an electrolytic cell by a difference of potential infinitely little different from the electromotive force of polarisation p, an infinitely slow separation of ions takes place. By including a very large resistance in circuit, the process will be reversed and a very feeble current will flow through the cell, whose electromotive force will be infinitely little different from p. In each case, p will be independent of the strength of the current provided it is small. From the second law of thermodynamics, Helmholtz finds that in such a cell no secondary heat will be produced as long as p is independent of the absolute temperature 0. If, on the contrary, p is a function of e, a quantity of heat measured by

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must be supplied to the cell in order to maintain the temperature constant, in the case where the process is reversed. Here the current of strength I traverses the cell for a time t, and a is the thermal equivalent of a unit of work. This result has been tested by the experiments of Czapski, Gokel, and Jahn, and has been found to be correct. In many cases, however, the actions are not reversible. Pebal believes that Helmholtz's result may be extended to non-reversible actions somewhat on the following grounds :

In the majority of cases to which the second law of thermodynamics is applied, as, for instance, to the theory of the steam-engine, &c., the immediate circumstances are not strictly reversible. Rather they have to be approximated to by an ideal set of conditions, in which every finite difference of temperature and every sudden transformation of energy is avoided. In a similar manner, Helmholtz's result may possibly be made available for all electrolytic actions by replacing sudden transformations of energy by reversible processes.

Taking as an ideal case that of a Grove's gas-battery, the formula 1 will give correctly the amount of heat produced by secondary causes. In the actual circumstances when bubbles of gas rise through the

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