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A Convenient Standard Cell Proceedings of the Iowa Academy of Science Volume 22 Annual Issue Article 23 1915 A Convenient Standard Cell Dieu Ung Huong State University of Iowa J. N. Pearce State University of Iowa Let us know how access to this document benefits ouy Copyright ©1915 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Huong, Dieu Ung and Pearce, J. N. (1915) "A Convenient Standard Cell," Proceedings of the Iowa Academy of Science, 22(1), 169-174. Available at: https://scholarworks.uni.edu/pias/vol22/iss1/23 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact [email protected]. Huong and Pearce: A Convenient Standard Cell CONVENIENT STANDARD CELL 169 A CONVENIENT STANDARD CELL. DIED UNG HUONG AND J. N. PEARCE. Until receptly both the Clark and the Weston cells have served as standard sources of electromotive force. Both of these con­ sist ofl an amalgam of a metal as the anode covered by a satur­ ated solution of the sulphate of the metal and this in conjunc­ tion with mercury and mercurous sulphate which serves as the cathode. Clark cell: (Hg-Zn)-ZnS04-Hg2SO,-Hg. Weston cell: (Hg-Cd)-CdSO,-Hg2SO,-Hg. For various reasons the acceptance of the Clark cell as a standard has been discontinued. The Weston cell, chiefly on account of its approximately negligible temperature coefficient, is now the sole accepted standard of electromotive force. The ohject, of this investigation was to make a study of amal­ gam cells o:ll the Weston type and to determine whether thel'W! may not be other amalgam cells which might serve as suitable and convenient standards. of electromotive force. With this idea in mind, amalgams of several metals were pre­ pared and used as anodes against the mercury as cathode. Of these the copper amalgam cells appeared most favorable. They present at least one distinct advantage, viz.., all of the con­ stituents of the cell are easily obtained in a very pure form. A number o:li these cells have been prepared, their reproduci­ bility has been determined and their temperature coefficients measured. EXPERIMENTAL. Mercury. The so-called "chemically pure" mercury (Kahl­ baum) was further purified by vigorously shaking with pure dilute nitric acid. The acid and the dissolved impurities were then completely removed by shaking ten times with successive portions of hot distilled water. The mercury and the water were then separated by means of a separatory funnel and the mercury allowed to trickle through a dry filter. Mercurous Sulphate. Kahlbaum's chemically pure mercurous sulphate was shaken with five successive portions of a saturated solution of copper sulphate. After each shaking the mercurous: Published by UNI ScholarWorks, 1915 1 Proceedings of the Iowa Academy of Science, Vol. 22 [1915], No. 1, Art. 23 170 IOWA ACAD:E'MY OF SCIENCE CONVEN sulphate was allowed to settle and the supernatant liquid de­ solution of copper sulp.l canted. paraffin, cork and sealin Ooprper Sulphate. The pure salt was further purified by re­ bubble to allow for the crystallization. Clear stock crystals were carefully picked and All measurements of dissolved in hot water. This solution was then filtered and al­ both 18°±.02 and 25°±.0 lowed to crystallize. Clear crystals of about the size of a pea electrically heated and were picked and these were washed with distilled water .. The by means of the familim saturated solution was preserved for preparing the cells. relay system. The temp Amalga.m. The copper amalgam was prepared electrolytically. mometer, graduated in O For this purpose a standard solution of copper sulphate con­ A recently certified Ci taining exactly 25 grams of copper per liter was prepared. To was placed in a deep. gl make an amalgam of any desired concentration, a given weight cotton. Owing to its higl of the pure mercury was placed in the electrolyzing vessel and the cell were immersed temperature of the cell · the number of cc containing the desired weight of copper was imbedded in the Clark 1 added from a burett~. Sufficient water was added to give a cell corrected for the tern workable solution volume. Contact with the mercury cathode was made by means of a small platinum wire sealed into the No readings of the ele' the cells had come to tem end of a narrow glass tube containing the mercury which made was considered as establi the contact with the copper wire terminal. In order to hasten intervals, were identical. the electrolytic deposition of the copper, the platinum spiral anode was rapidly rotated by means of a small electric motor. three hours of the time < The measurements. of The current was allowed to pass until a few drops of the solu­ means of a 5-dial Wolff tion tested with potassium fierrocyanide gave no indication of 1 sitive galvanometer ( typE copper. After deposition the amalgam was quickly separated The temperature coeffi, from the supernatant liquid by means of a stop-cock at the bot­ expression : tom of the electrolyzing vessel. Cells. Only cells of the "H-type" were used and these were specially constructed for immersion purposes. According to where ·E and E are th Wolff and Waters, the size and dimensions of the cell do not 18 25 and 25 °, respectively, ar affect the electromotive force but they do affect the rapidity attempt was made to der: with which the cells assume the ·temperature equilibrium. temperature coefficients. The cells were made up in the usual. The amalgam and The results obtained , mercury were introduced into their respective limbs by means Tables I to V show the r of pipettes, each to the depth o:li one and one-half centimeters. tical columns repr~sent t] Upon the mercury was placed a two centimeter layer of a thick dates and the deviations 1 paste consisting of the mercury, mercurous sulphate and the Tables VI and VII giv1 saturated solution of copper sulphate. In each limb was next Weston cells set up by G placed a two centimeter layer of clear picked copper sulphate for comparison. Their I! crystals and the cell was then nearly filled with the saturated their results show greatei the copper amalgam cells results for the eight coppe https://scholarworks.uni.edu/pias/vol22/iss1/23 2 Huong and Pearce: A Convenient Standard Cell JIENCE CONVENIENT STANDARD CELL 171 : supernatant liquid de- solution of copper sulphate. The limbs were then sealed with paraffin, cork and sealing wax, care being taken to admit an air 1 further purified by re­ bubble to allow for the expansion of the liquid. :re . carefully picked and All measurements of the electromotive force were made at vas then filtered and al­ both 18°±.02 and 25°±.02. The constant temperature bath was about the size of a pea electrically heated and the temperature electrically controlled ith distilled water. The by means of the familiar contact toluol regulator and telegraph reparing the cells. relay system. The temperatures were read on a certified ther­ prepared electrolytically. mometer, graduated in 0.10° and readable to 0.01°. of cop,per sulphate con­ A recently certified Clark cell was used as reference cell. It r liter was prepared. To was placed in a deep, glass beaker and carefully cov_ered with mtration, a given weight cotton. Owing to its high temperature coefficient the beaker and ) electrolyzing vessel and the cell were immersed in the water of the bath. The exact ed weight of copper was temperature of the cell was read from a certified thermometer ter was added to give a imbedded in the Clark cell and: the electromotive force of the ith the mercury cathode cell corrected for the temperature. mm wire sealed into the No readings of the electromotive force were made until after the mercury which made the cells had come to temperature equilibrium. This equilibrium iinal. In order to hasten was considered as established when readings, taken at half-hour per, the platinum spiral intervals, were identical. In no case were readings taken within Jf a small electric motor. three hours of the time of immersion. a few drops of the solu­ The measurements of the electromotive force were made by d~ gave no indication of means of a 5-dial W oiff potentiometer in connection with a sen­ m was quickly sep.arated sitive galvanometer (type "H", L. and N.). of a stop-cock at the bot- The temperature coefficients were calculated by means of the expression : dE E 18-E,0 were used and these were -=--, purposes. According to dt E 1 s · t msions of the cell do not where E 18 and E 25 are the electromotive forces measured at 18° ey do affect the rapidity and 25°, respectively, and t is the tempera·~ure interval. No attempt was made to derive a more elaborate exp.ression for the ~erature equilibrium. temperature coefficients. isual. The amalgam and The results obtained are recorded in the following tables. ~esp.ective limbs by means Tables I to V show the results for five different cells. The ver­ and one-half centimeters.. tical columns repr~sent the successive measurements of different :entimeter layer of a thick dates and the deviations of each from the mean in 0.00001 volt. rcurous sulphate and the Tables VI and VII give the records of two Clark and two e. In each limh was next Weston cells set up by Guthe and von Ende.
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