Clark and Weston standard cells . ainment of saturation equilibrium. With white samples of mer-curous sulphate, one-third the volume of mercury was added withthe crystals of zinc or cadmium sulphate in making up the eliminate possible influence of size of grain the paste was stirredas little as possible in its preparation. Wolff. IWaters.\ Clark and Weston Standard Cells. 29 THE CELLS. For facility in filling and sealing the H type was adopted. Thesize and dimensions, although not affecting the electromotive forcedetermine the polarization produced by the passage of a currentand the r
Clark and Weston standard cells . ainment of saturation equilibrium. With white samples of mer-curous sulphate, one-third the volume of mercury was added withthe crystals of zinc or cadmium sulphate in making up the eliminate possible influence of size of grain the paste was stirredas little as possible in its preparation. Wolff. IWaters.\ Clark and Weston Standard Cells. 29 THE CELLS. For facility in filling and sealing the H type was adopted. Thesize and dimensions, although not affecting the electromotive forcedetermine the polarization produced by the passage of a currentand the rapidity with which the cell assumes the temperature of itssurroundings. Figure 3, drawn to half scale, gives the approximatedimensions of the cells used at the Bureau. Especial care was takenin sealing in the platinum wires and subsequent annealing. Asrecommended by Hulett, the platinum wire inside the cell wascovered in most cases wTith a thin layer of glass to within 1 mm or PASTE- Hg- SOLUTION <-CRYSTALS- . AMALGAM- Fig. -SE»L <—AMALGAM Fig. 4. Sectional Views of Standard Cells {Half size). less from the end. The wTire should not be larger than B. & 28, to reduce the liability of cracking. No. 32 was used inmost of our cells. The Clark cells nevertheless frequently cracked at the point wherethe platinum terminal was sealed into the amalgam limb. Thismay be avoided by a construction recommended by the Reichsanstaltand shown in figure 4, in which the platinum terminal of the amal-gam limb is sealed into a side tube while the amalgam is stillliquid, contact being made by sucking the amalgam up into thistube. The platinum wire extends downward about 2 cm below the 8919—07 3 30 Bulletin of the Bureau of Standards. {, point at which it is sealed into the tube and the amalgam shouldcover only its lower half, thus preventing the glass from crackingat the seal. This construction also reduces the chance of contactbetween the platinum and the electrolyte,
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