. Manual of physico-chemical measurements. of an H-shaped vessel (first employed by Lord Rayleigh), thebottom of one side of which is covered with a layer of mercury, theother side containing an amalgam of 9 parts mercury and 1 partzinc (Fig. 145). The zinc amalgam is poured in when warm, andsolidifies on cooling. The mercury is covered with a thick paste ofniercurous sulphate, zinc sulphate, and mercury, rubbed up with asaturated zinc sulphate solution. On the top of this, and also on thetop of the mercury, there come zinc sulphate crystals, the whole beingthen filled with saturated zinc sulp
. Manual of physico-chemical measurements. of an H-shaped vessel (first employed by Lord Rayleigh), thebottom of one side of which is covered with a layer of mercury, theother side containing an amalgam of 9 parts mercury and 1 partzinc (Fig. 145). The zinc amalgam is poured in when warm, andsolidifies on cooling. The mercury is covered with a thick paste ofniercurous sulphate, zinc sulphate, and mercury, rubbed up with asaturated zinc sulphate solution. On the top of this, and also on thetop of the mercury, there come zinc sulphate crystals, the whole beingthen filled with saturated zinc sulphate solution to within 1 or 2 the top. The cell is closed by paraffin poured on when hot, acork disc, and melted resin. For use the cell is set on a saddle-shaped support provided with binding screws. The electromotiveforce is 0-0002 volt smaller than that of the element described above. The Clark cell suffers from the drawback that its electromotive ^ Kahle, Ztschr. f. TiistrumenienkuiuU, 12, 130, 1892. ELECTRICAL MEASUREMENTS 195. Fig. 146. force varies greatly with the temperature, and that the electromotiveforce corresponding to each temperature is only slowly element should therefore be made as smalland narrow as possible in order to follow thechanges of temperature rapidly. For very exactmeasurements it must be kept in a thermostat. The electromotive force is diminished bystrong currents ; OOOl amp. can be taken off fora short time, OOOOl amp. for any length of timewithout causing a noticeable error. The cellsoon recovers when the circuit is opened. Other Normal Elements.—On account ofits great temperature coefficient and tempera-ture lag, attempts have been made to replacethe Clark element by others. Favourable accounts have been givenof Gouys element,-- which is composed as follows :—An amalgamatedzinc rod is immersed in a 10 per cent solution of zinc sulphate ( 106), which rests on a layer of mercury. Precipitated mercuricoxide acts as dep
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Keywords: ., bookcentury1800, bookdecade1890, bookpublisherlondo, bookyear1894
