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Rh and when made as directed below it has at t° C. an electromotive force Et volts, such that

E = 1·0184−0·0000406 (t−20)−0·00000095 (t−20)2+ 0·00000001 (t−20)°.

After the platinum wires have been sealed through the glass, a little aqua regia is placed in the cell legs until bubbles of gas arise from the platinum, when it is thrown out and replaced by a solution of mercurous nitrate. Then, by the use of another piece of platinum as anode, mercury is electrolytically deposited upon the platinum, which may also be amalgamated by making it white hot in a Bunsen flame and plunging it in mercury. To prepare the cadmium amalgam, one part of pure cadmium is dissolved in six parts of pure mercury, and the product while warm and fluid is placed in one . 3.—Lord Rayleigh’s H form of Standard Voltaic Cell.

limb of the cell and warmed, to ensure perfect contact with the platinum wire. The cadmium sulphate solution is prepared by digesting a saturated solution of cadmium sulphate with cadmium hydroxide to remove free acid, care being taken not to raise the temperature above 70° C., and then by digesting it still further with mercurous sulphate until no more precipitation occurs. The cadmium sulphate solution must be saturated and have free crystals of the salt in it. The mercurous sulphate must be free from acid, and made neutral by trituration with finely divided mercury. In making the paste, so much cadmium sulphate must be added that a saturated solution of that salt is formed and is present in the cell. The cell has the electromotive force above stated if the amalgam of cadmium has from 6 to 13 parts of mercury to 1 of cadmium. The German investigators seem to have a great preference for the H form of cell, but it is clear that a narrow tubular cell of the British board of trade form not only comes more quickly to the temperature of the water bath in which it is placed, but is more certain to be wholly at one temperature. In a modification of the H form devised by F. E. Smith, of the National Physical Laboratory (Phil. Trans., A, 207, pp. 393–420), a contraction formed in the side of the vertical tube tends to hold the contents in place. Fig. 4 shows this cell, hermetically sealed, mounted in a brass case.

In cases when great accuracy is not required, a Daniell cell can be used as a standard of electromotive force. The form designed . 4.—Method of mounting Weston Normal Cell. Brass case removed.

by J. A. Fleming (Phil. Mag., 20, p. 126) consists of a tube, one leg of which contains a rod of pure amalgamated zinc, and the other a rod of freshly electrotypes copper. The legs are filled with solutions of zinc sulphate and copper sulphate, the zinc rod being in the zinc sulphate and the copper rod in the copper sulphate. When so made, the cell has an electromotive force of 1.072 volts and no sensible temperature variation. The solutions are made by dissolving the purest recrystallized sulphate of copper and sulphate of zinc in distilled water. For the zinc solution, take 55.5 parts by weight of crystals of zinc sulphate (ZnSO47OH2) and dissolve in 44.5 parts by weight of distilled water; the resulting solution should have a specific gravity of 1.200 at about 20° C. For the sulphate of copper solution, take 16.5 parts by weight of pure crystals of copper sulphate (CuSO45OH2) and dissolve in 83.5 parts by weight of water; the resulting solution should have a specific gravity of 1.100 at 20° C. The solutions should be adjusted exactly to these densities and kept in stock bottles, from which the reservoirs of the cell should be filled up as required. A form of potentiometer employing a vibration galvanometer and suitable for alternating current measurement by null methods has been devised by Dr Drysdale (see Proc. Phys. Soc. Lond. 1909, 21, 61.)

See J. A. Fleming, Handbook for the Electrical Laboratory and Testing Room, vol. i. § London, 1903)—vol. i contains on pp. 108–110 an extensive list of various original memoirs published on the Clark and Weston cells; G. D. Aspinall Parr, Electrical Engineering Measuring Instruments (London, 1903); W. C. Fisher, The Potentiometer and its Adjuncts (London, 1906).

POTENZA (anc. Potentia), a town and episcopal see of Basilicata, Italy, capital of the province of Potenza, 103 m. by rail E. by S. of Naples. Pop. (1901), 12,313 (town), 16,163 (commune). Situated 2700 ft. above sea-level on an isolated hill above the Basento (anc. Casuentus), it is much exposed to winds and has a far more northerly climate than its position (40° 40′ N.) implies, and is indeed one of the coldest places in Italy (mean temp. Jan 37.8°, July 70.9°, for whole year 53° F.). It has been almost entirely rebuilt since the earthquake of 1857. It has a school of the industrial arts and sciences, grows good wine, and makes bricks.

The ancient Potentia lay some 470 ft. lower, by the river. Its name shows that it was of Roman origin, and its importance was no doubt due to its position at the intersection of the road leading west to the Via Popillia and north-east to the Via Appia, with the Via Herculia. No remains are visible, but a considerable number of inscriptions have been found.

Potentia must be distinguished from Potentia in Picenum, on the Adriatic coast, near the modern Porto di Recanati, a colony founded in 184, the same year as Pisaurum, but of which little is known.

The abandonment of the old site and the erection of the new town probably date from the earthquake of 1273., By the Angevines Potenza was made a domain of the San Severino family; in the beginning of the 15th century it was held by Francesco Sforza, and in 1435 it passed to the Guevara family; the Loffredi, who succeeded by marriage, continued in possession till the abolition of the great fiefs. In 1694 there was a severe earthquake; and the more terrible earthquake which on the 16th and the 17th of December 1857 passed through southern Italy, and in Basilicata alone killed 32,475 persons, laid the greater part of Potenza in ruins. In 1860 it was the first town to rise against the Neapolitan government.

 POTGIETER, EVERHARDES JOHANNES (1808–1875), Dutch prose writer and poet, was born at Zwolle, in Overyssel, on the 17th of June 1808. He started life in a merchant’s office at Antwerp. In 1831 he made a journey to Sweden, described in two volumes, which appeared at Amsterdam in 1836–1840. Soon afterwards he settled in Amsterdam, engaged in commercial pursuits on his own account, but with more and more inclination towards literature. With Heije, the popular poet of Holland in those days, and Bakhuizen van den Brink, the rising historian (see also ), Potgieter founded De Muzen (“The Muses,” 1834–1836), a literary review, which was, however, soon superseded by De Gids (“The Guide”), a monthly, which became the leading magazine of Holland. In it he wrote, mostly under the initials of “W. D——g,” a great number of articles and poems. The first collected edition of his poems (1832–1868) appeared in 2 vols. (Haarlem, 1868–1875), preceded by some of his contributions to De Gids, in 2 vols. also (Haarlem, 1864), and followed by 3 vols. of his Studien en Schetsen (“Studies and Sketches,” Haarlem, 1879). Soon after his death (Feb. 3, 1875) a more comprehensive edition- of Potgieter’s Verspreide en Nagelaten Werken (“Miscellaneous and Posthumous Works”) was published in 8 vols. by his friend and literary executor, Johan C. Zimmerman (Haarlem, 1875–1877), who likewise supervised a more complete edition of Potgieter’s writings which appeared at Haarlem in 1885–1890 in 19 vols. Of Potgieter’s Het Noorden in Omtrekken en Tafreelen (“The North in Outlines and Pictures”) the third edition was issued in 1882, and an édition de luxe of his poems followed at Haarlem in 1893. Under the title of Personen en Onderwerpen (“Persons and Subjects”) many of Potgieter’s criticisms had collectively appeared in 3 vols. at Haarlem in 1885, with an introduction by Busken-Huet.

Potgieter’s favourite master among the Dutch classics was Hooft, whose peculiarities in style and language he admired and imitated. The same vein of altruistic, if often exaggerated and biased, abhorrence of the wonted conventionalities of literary life runs through all his writings, even through his private correspondence with Huet, parts of which have been published. Potgieter remained to his death the irreconcilable enemy of the Dutch “Jan Salie,” as the Dutchman IS nicknamed who does not believe in the regeneration of the Dutch people. Potgieter held up the Netherlanders of the golden age of the