Abstract: Aqueous iodine-iodide etching solutions are employed in the recovery of precious metals. Elemental iodine is precipitated from spent etching solutions and used to supply both the iodine and iodide of new etching solutions. Prior to extraction of the elemental iodine, used solutions, if not substantially contaminated, may be oxidized and recycled for further precious metal recovery. Aqueous etching solutions of hydriodic acid and iodine, or of ammonium iodide and iodine may be employed. Etching in such solutions, as well as in solutions of iodine and an alkali metal iodide, such as potassium iodide, may be accelerated by the use of small amounts of hydrogen peroxide (or equivalents) during etching.

Abstract: A process for maintaining financial records, such as checkbook balances, in which a checking account user employs a hand-held calculator to record the usual checkbook data electronically. The calculator is programmed to calculate and memorize a first running balance dependent upon numeric data entered by the user. A financial institution maintains a second running balance dependent upon the user's checks and deposits and periodically provides the user with a magnetic card on which the second running balance and other data have been recorded. The card is read by the user's calculator to balance the user's checkbook.