Tin may be easily estimated by electrolysis; it can be separated from
its hydrochloric acid solution, or from its double salt with ammonium
oxalate, as a beautiful silver gray coating on the platinum. When the
ammonium oxalate is substituted by the potassium salt, the operation
becomes more difficult, as a basic salt is formed at the opposite
pole, and is not easily reduced. If the tin is separated from an acid
solution, the current must not be interrupted while the washing takes
place, a precaution which it is not necessary to follow when the
ammonium oxalate is used. When the tin is dissolved from the platinum
dish, it acts like the zinc; that is to say, a black coating is left on
the electrode.