Preparation of Silver for Use in Walden Silver Reductor G. FREDERICK SMITH AND F. WM. CAGLE, JR., Noyes Chemical Laboratories, University of Illinois, C’rbana, I l l .
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ILVER for use as reducing agent in the Walden silver reductor ( 1 ) is usually prepared by the displacement of silver from a slightly acidified, concentrated solution of silver nitrate by the action of copper in the form of heavy sheet or large-gage wire. In the authors’ hands, silver prepared in this manner has been so finely divided that the flow of solution through the reductor is too slow or the operation requires reduced pressure. The flow is further retarded by the deposition of silver chloride and regeneration is difficult. The method described here for the preparation of silver reductor metal eliminates these difficulties. The process involves preparation of electrodeposited silver under conditions which result in “silver tree” type aggregates, minute yet distinctly granular, brilliantly reflecting crystals, of low apparent dmsity with a high ratio of surface to mass. Electrodeposition of Silver a s Tree Silver. The electrolyte consisted of about 500 grams of silver nitrate dissolved in 2500 ml. of water, slightly acidified by the addition of nitric acid and contained in a 4-liter beaker. The cathodes &ere of heavy-gage platinum with heavy “lead in” conductor extensions. Each of two cathodes was 10 cm. square and was suspended in the electrolyte by use of heavy co per bus bar connections to a source of direct curient. The anoie \vas either a silver rod 10 to 25 mm in diameter and 200 mm. long or a similar amount of silver as a heavy-gage rectangular sheet, in either case suspended in the center of the silver nitrate electrolyte with the platinum cathodes placed a t the outer edges of the deposition cell. A current of 60 to 70 amperes a t a voltage of 5 to 6 volts served to deposit the silver in the proper form. This electrical energy is best supplied by use of a motor generator set. The electrolyte need not be stirred or cooled. The silver deposits in mosslike, multibranched, brilliantly refracting crystals of silver in the four outside edges of the platinum cathodes, from which it may be dislodged by gentle tapping. About 30 grams of the silver in this form occupy a volume of 40 to 50 ml. or sufficient for one correctly designed Walden reductor tube. Preparation of Walden Reductor Apparatus. h reductor column of the usual Jones reductor type ( 1 ) held a sufficient quantity of silver preparation for satisfactory operation. The silver was introduced into the tube above a small plug of glass wool and then compressed within the tube as it was inserted (a blunt-ended ramrod device was used) to as great an extent as required without restricting the free flow of solution through the column.
The procedure described requires special equipment for its preparation, such as large silver anodes and platinum cathodes together with a source of low voltage-high amperage direct current. For this reason silver of suitable form should be ultimately supplied through regular trade channels. The reductor, because of its limited quantity of silver and its abnormally small apparent density, requires more frequent regeneration. These limitations are far outweighed by the resultant advantages. LITERATURE CITED (1) Walden, Hammett, and Edmonds, J . Am. Chem. Soc., 56, 350
(1934). RECEIVED S o v e m b e r 9. 1946.
Volumetric Analysis. Titration Methods. Acid-Base, Precipitation and Complex-Formation Reactions. I . .\I. Kolthof and V . A . Stenger. Volume 11. Second revised edition. xiii 374 pages. Intersrience Publishers, Inc., 215 Fourth Ave., New Tork 3, N. Y.. 1947. Price, $8.00.
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This volume of the second edition corers the practical aspects of volumetric titrations except for oxidation-reduction reactions, which are to be included in Volume I11 scheduled for publication in late 1948. (Volume I of this revised series, published in 1942, covered the theoretical fundamentals.) Revision has been thorough. Many new methods, modifications. and recent references are included. Volume I1 is divided into three main parts: (A) -1pparatus and General Principles, (B) .kcid-Base Reactions, and ( C ) Quantitative Precipitation and Complex-Formation Reactions. P a r t X contains many practical pointers about the calibration and use of volumetric apparatus of all types and the selection of primary and secondary standards. Numerous tables useful in calibrating glassware are included. P a r t B describes the indicators and primary standards available for acid-base reactions and then considers a large number of actual examples of acid-base titrations including displacement titrations hydrolytic precipitations, and special methods. Procedures and notes describing variations in procedure, interferences, and applications are given for most of the examples. P a r t C consists of a large chapter on argentometric procedures and two smaller chapters on mercurimetry and other precipitation methods. As in P a r t B, the indicators, primary and secondary standards, and proredures are adequately described and annotated. The authors have not intended to cover exhaustively all applications of volumetric analysis. They have given a broad selection of useful and reliable methods, trying to emphasize the fundamental principles involved. Nevertheless, the reader will find within this volume examples of determinations of substances of interest to all fields of pure and applied chemistry. Emphasis has been placed upon the attainment of the highest possible precision in the methods described in the volume. The reader can then determine for himself the refinements necessary for his particular problem. T h e authors have apparently tried o u t most of the procedures themselves, and have given many valuable comparisons of the relative merits of the methods. Only a very few minor and obvious errors in typography were noted, except that the last equation on page 27 and the equation given in the Ct rather t h a n - Ct if Ct illustration on the next page should read has the signs a s given in the table on page 22. T h e binding is good and the paper about average. This reviewer would not hesitate to recommend this book to anyone interested in the practice of volumetric analysis and hopes t h a t the third volume will not be long delayed. LYNNEL. MERRITT,JR.
Reductor Performance. A molar solution of hydrochloric acid was prepared which contained 0.1 mole of ferric chloride. The reductor was rinsed, using molar hydrochloric acid, and tested starting with the reductor filled to the top of the silver with molar hydrochloric acid. The top reservoir was filled with the ferric chloride solution and the lower stopcock opened fully. The solution to be reduced was continuously passed through the reductor until it was no longer quantitatively reduced. Four hundred milliliters of the 0.1 molar ferric chloride were reduced in 5 minutes of flow. This amount of reduction nould account for the quantity of iron to be reduced in 12 to 15 ordinary analyses. The reductor is completely rinsed in an actual quantitative determination by the passage of 100 ml. of molar hydrochloric acid in 5 equal portions, each consecutive portion being allowed to pass through the reductor down to the level of the silver. Reductor Regeneration. To free the silver from deposited silver chloride, it is rinsed with water and filled completely with dilute 1 to 3 reagent ammonium hydroxide. The silver chloride is removed completely from the silver by this treatment and may be rinsed out of the reductor tube with water followed by molar hydfochloric acid and is then ready for re-use. I t is always advisable to allow the dilute ammonia to stay in contact with the silver for 5 to 10 minutes before rinsing it from the reductor, although the solution of the coating of silver chloride seems to be removed instantly. The regenerated reductor performs in every way precisely as indicated, no matter how many times it is regenerated. As a precautionary measure the ammoniacal solution of silver chloride should be promptly discarded or acidified.
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