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<p>[QUOTE="Frankcoins.com, post: 1435178, member: 16048"]Silver dissolves readily in nitric acid, but does not react with sulfuric acid. In any case, coin dip has about 5% sulfuric acid, about as strong as vinegar. </p><p><br /></p><p>Silver ions in the dip are not from the reaction of removing tarnish, but from reactions by foreign ions. </p><p><br /></p><p>From Metallurgical Transactions B, Volume 21, Issue 3, pp.419-427</p><p><br /></p><p>The rotating disk technique was used to study silver dissolution with thiourea as a function of sulfuric acid, ferric sulfate, and thiourea concentrations. The effect of many foreign ions (Mn, Cu, Co, Ca, Na, etc.) and various additives was also examined. The dissolution of silver was zero order with sulfuric acid, first order with ferric sulfate, and second order with thiourea. Among the foreign ions, copper had a dramatically negative effect. The strong oxidants such as hydrogen peroxide and manganese dioxide were also detrimental for silver dissolution. According to the temperature effect studied (5 °C to 35 °C), the activation energy was 22.6 kJ/ mole. Silver does not dissolve with thiourea in the absence of ferric ions. Sulfuric acid does not participate in the dissolution reaction. The most important parameter for silver dissolution is the ferric sulfate/thiourea ratio. In excess ferric sulfate, a solid silver-thiourea complex is formed, which precludes transfer of silver into solution. In excess thiourea, the free thiourea reacts with formed solid silver-thiourea complex, and silver goes into the solution, predominantly as the dimers of AgTU+ 3 complexes. The solid silver-thiourea complex in question was characterized by various spectroscopic, microscopic, and chemical analysis techniques. According to chemical composition, it corresponds to Ag2SO2·3TUH2O compound. </p><p><br /></p><p><br /></p><p>It would appear that dipping silver war nickels and "golden" dollar coins, which contain manganese, contaminates the dip causing silver ions to be in solution[/QUOTE]</p><p><br /></p>
[QUOTE="Frankcoins.com, post: 1435178, member: 16048"]Silver dissolves readily in nitric acid, but does not react with sulfuric acid. In any case, coin dip has about 5% sulfuric acid, about as strong as vinegar. Silver ions in the dip are not from the reaction of removing tarnish, but from reactions by foreign ions. From Metallurgical Transactions B, Volume 21, Issue 3, pp.419-427 The rotating disk technique was used to study silver dissolution with thiourea as a function of sulfuric acid, ferric sulfate, and thiourea concentrations. The effect of many foreign ions (Mn, Cu, Co, Ca, Na, etc.) and various additives was also examined. The dissolution of silver was zero order with sulfuric acid, first order with ferric sulfate, and second order with thiourea. Among the foreign ions, copper had a dramatically negative effect. The strong oxidants such as hydrogen peroxide and manganese dioxide were also detrimental for silver dissolution. According to the temperature effect studied (5 °C to 35 °C), the activation energy was 22.6 kJ/ mole. Silver does not dissolve with thiourea in the absence of ferric ions. Sulfuric acid does not participate in the dissolution reaction. The most important parameter for silver dissolution is the ferric sulfate/thiourea ratio. In excess ferric sulfate, a solid silver-thiourea complex is formed, which precludes transfer of silver into solution. In excess thiourea, the free thiourea reacts with formed solid silver-thiourea complex, and silver goes into the solution, predominantly as the dimers of AgTU+ 3 complexes. The solid silver-thiourea complex in question was characterized by various spectroscopic, microscopic, and chemical analysis techniques. According to chemical composition, it corresponds to Ag2SO2·3TUH2O compound. It would appear that dipping silver war nickels and "golden" dollar coins, which contain manganese, contaminates the dip causing silver ions to be in solution[/QUOTE]
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