Some metals, when dissolved in an acid, produce solutions, from which the metal can be recovered by immersing in the solution another, as the chemists say, more active, metal. The latter dissolves and the original metal is “freed” from solution, sometimes forming beautiful crystals or simply coating the other piece of metal. For instance, iron, zinc, and aluminum are capable of releasing copper from solutions containing copper. Likewise, copper (but also iron, zinc, and aluminum) can release silver from its solutions.
In this experiment, a piece of silver has been pre-dissolved in nitric acid, forming a water-soluble salt, named silver nitrate. A solution of silver nitrate in water (10 weight percent) is colorless and looks like pure water. If a piece of copper (say, a copper wire, or sheet made of copper, or even a penny) is dropped in the solution, copper starts to “displace” silver. Copper dissolves forming a beautiful blue solution and the silver is released on the surface of the copper piece in the form of small shiny needle-like crystals. If the copper piece is shaped to have a number of branches, a silver “tree” (or a silver “marine plant”) will be formed as shown, in the picture. The experiment is usually completed within 5-10 minutes. One important thing to remember is that silver was not made out of water or out of “nothing”, although it may appear so; the silver was present in the solution but it was not visible until the chemical reaction with the copper “released” it. During the middle ages, charlatans could have claimed that they “converted” (or as they used to say, “transmuted”) copper into silver but this is not the case. The silver can be scraped off from the copper surface and collected. If heated to very high temperature (if the appropriate heating device is available) and then cooled, it will form a nice silver chunk.