Valuable money

Not all the currencies are of the same value. Some devaluate quickly, others get damaged easily, still others get lost. If a scientist is equipped with any kind of meter, he or she can instantly assess the usefulness of two different coins. It is enough to place a piece of blotting paper saturated with any kind of solution, e.g. saliva. 'Good coins' like Polish old aluminium grosz or Italian 10 lire coin act quite well when put together with brass new zloty or copper eurocents. It is enough to use just a few of them to light a small LED diode.

This was one of the greatest inventions - a cell, or a Voltaic pile. He placed together a several pairs of alternating zinc and silver coins separating each pair by cloth soaked in acid. Such a pile generated quite considerable sparks. What is more, the pile was easy to disassemble if you needed the money. (in our pile in the picture the electronegative aluminium coins digest quickly and become thinner).