Magic Spoon

 

A metal spoon placed in the hot water disappears. It is made of  low temperature melting alloy.

Materials
Soldering iron, dental impression material, plastic coffee spoon, tea cup, tea bag, electric kettle, ceramic plate, burner, test tube, balance

Chemicals
Hot water, Wood's metal, (you can prepare it by melting 10 g bismuth, 2 g cadmium, 5,4 g lead and 2,66 g tin).

Experimental

  • Prepare Wood's metal by melting 10 g bismuth, 2 g cadmium, 5,4 g lead and 2,66 g tin.
  • Pour the melted alloy on a ceramic plate.
  • After cooling crush it on a small pieces.
  • Prepare enough dental impression material according to the instructions.
  • Press the coffee spoon into the dental impression material to make a mold (Fig. 1).
  • Wait to get hard according to the instructions and than remove the spoon.
  • Place the Wood's metal pieces in the mold and melt them with the tio of the soldering iron.
  • If needed add more Wood's metal in the mold.
  • After cooling, remove the metal spoon and if necessary make some corrections of the shape (Fig. 2). 

Fig. 1. Mold

Fig. 2. Magic spoons
  • To demonstrate the magic spoon, boil water and place it in the tea cup with a tea bag.
  • Then, stir the tea with the magic spoon.
  • Remove the spoon from the cup and ask the audience what happened with the spoon.

Observation and Discussion

Wood's metal is an alloy consisted of lead, tin, bismuth and cadmium. It is also known as Lipowitz's alloy, Bendalloy, Cerrobend, and Pewtalloy. It is a fusible alloy with a melting point of approximately 70 °C. When a spoon made of this alloy is inserted in a cup with hot tea it melts. It is unusually for a metal – metal alloy to have such a low melting temperature.

Safety Tips
Wood's metal is toxic because it contains lead and cadmium. Therefore contact with the bare skin is thought to be harmful. Wearing protective gloves are required when handling it. Cadmium poisoning carries the risk of cancer and damage to the liver, kidneys, nerves, bones, and respiratory system.
Take precautions to avoid electric shock. Keep electrical equipment away from water or any other liquid, conductive or not.