Some Experiments with Primary Cells in Silicic Acid Gels OYCO F. STEINBACH City College of Nelo York, New York
HE STUDY of primary cells can be nicely supTplemented by preparing them in a medium of a silicic acid gel. The results obtained are interesting and instructional. The familiar lead tree, which is generally obtained by pressing a piece of zinc or tin into the top of a silicic acid gel containing lead salt, can be obtained in 24 hours from the primary cell ZnlZnS0,11Pb(N03)nlPb. It seems to the author that the principle involved in the formation of the lead tree is more clearly illustrated by the primary cell than by the metho6 generally used. In an analogous fashion, it is possible to obtain a tin tree from the cell Zn ZnS0411SnClslSn. The following method was used to prepare these simple primary cells. Sodium silicate solution (sp. gr. 1.05) was mixed with an equal volume of acetic acid prepared from 60 ml. of the glacial acid diluted to 1 liter. The resulting silicic acid solution was divided into 20-ml. portions and 1 to 2 ml. of concentrated solutions of zinc sulfate, stannous chloride, or lead nitrate were added to the individual portions. The solutions were then poured into a U-tube in which a cotton plug had been placed in order to keep the catholyte and anolyte from freely miximg. After the gel bad set, strips of zinc and lead or tin were placed in their respective solutions. When the completed cells were tested with a galvanometer, a distinct deflection was obtained. The electrodes were then connected to each other (short circuited) and allowed to stand this way until the lead or tin trees had formed. The trees may be preserved by removing the electrodes and placing corks in the U-tubes. The Daniel cell, ZnlZnS0411CUSOrlCumay be prepared as another example of a primary cell. However, a gel must be prepared that is more acid than the above gels if a reasonable appearing copper tree is to be obtained with any rapidity, though copper is still deposited in the less acid gels. Another cell, which is also of the replacement type, is FelFeC1311CUS041Cu. The copper tree formed in this cell is somewhat superior
to the one formed in the Daniel cell. The last two cells are prepared by mixing equal volumes of 3 N HzS04 and sodium silicate solution of sp. gr. 1.16. Then 1 to 2 ml. of concentrated solutions of ferric chloride, copper sulfate, or zinc sulfate are added to 20-ml. portions of the silicic acid solutions. The solutions are poured into U-tubes as previously described and when the gels have set, the corresponding metal electrodes are placed in them. The cells may be tested by a galvanometer to show that they produce electrical energy and also to determine their polarity. The electrodes should then be short circuited and the cell should be observed over the period of a week as the copper tree forms. Upon removing the zinc or iron electrode, visual evidence of corrosion and solution can be distinctly observed. Closer inspection of the gel near the copper electrode will show that the gel is perceptibly less blue than portions further removed from the electrode. This is evidence of the diffusion and migration of cupric ions in the gel due to the cell reaction. The above cells may be modified by replacing the copper cathode by an inert electrode such as graphite. Upon short circuiting the electrodes, the graphite becomes copper plated a i ~ dlater a copper tree will form. Various combinations of metals and their salts may be used. For example, the cell MglMgS0411Pb(N03)2/Pb, when prepared in the gel of silicic acid made from acetic acid, produces a small lead tree in one hour while in three hours a fair-sized tree results, and in 24 hours a very dense tree is formed. Likewise, the cell MglMgSO,IISnC1$n was also prepared from the gel made from sodium silicate and acetic acid. In two hours a small tin tree was observed while in two days a good-sized tree resulted. A variety of primary cells have been prepared in gels of silicic acid. Trees of various metals have been obtained. The formation of the metal tree is clearly shown to be an electrochemical process.
THE DIRECT REACTIONS OF SOLIDS (Continued from Page 24) LITERATURE CITED
Bmc. "Die analytische Verwendung von Oxychinolin (Oxin)," Enke, Stuttgart, 1938. BLANK,J. CHEM.EDUC..20. 171 (1943). CAZENEUVE. Compt. rend.. 131, 346 (1900). EPHRAIM, Bn., 63, 1928 (1930); 64, 1210 (1931). FEIGL,"Qualitative Analysis by Spot Tests," translated b y Matthevs, 2nd ed., Nordeman Publishing Company, New York, 1939, pp. 115. 118, 119, 142. FEIGL, "Specific and Specml Reactions," translated by Oesper, Nordeman Publishing Company, New York, 1940, P 4 1 ; see also ( 5 ) , p. 224. FEIGL.Bn..56, 2083 (1923). FEIGL,Z. a d . Chem., 7 4 , 380 (1928). F E ~ AND L LEDERER,Monatsh., 45, 63 (1924). FISCHER, Z. angeu. Chem., 42, 1025 (1929). FUNKAND DITT.Z. anal. Cham., 93, 241 (1933).
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(12) HEDVALL, "Reaktionsfiihigkeit fester Stoffe," Barth, Leipzig, 1938. This includes a comprehensive review and a good bibliography. AND ELDH.Z. anorg. C h m . , 226,192 (1936). (13) HEDVALL AND H E ~ E R G Eibid., R , 128, 1 (1923). (14) HEDVALL AND HEUBERGER. ibid., 135, 49 (1924). (15) HEDVALL AND SCHILLER, ibid., 221, 97 (1935). (16) HEDVALL (17) HUrr~o,see bibliography in (12) and indexes of Chemical A bdracts. (18) TANDER. see biblioeraohv in (12) and indexes of Chemical (19) (20) (21) (22) (23) (24)
