Effect:
Procedure A - Two clear colourless liquids are mixed together. After a while, you point at the solution just as it suddenly turns deep blue; or
Procedure B - This can be run as a contest, with the solutions turning blue at different times, if at all.

What You Need:
- potassium iodate
- sodium sulfite
- sulfuric acid
- soluble starch
- water
- a pair of large test tubes for each volunteer

What You Do Before the Show:
- Prepare several mL of a solution of soluble starch in water
- Make Solution X of 0.5 g potassium iodate in 300 mL water
- Make Solution Y of 0.2 g sodium sulfite in 300 mL water plus 1 mL of 3 M sulfuric acid plus the soluble starch solution
- Mix equal volumes (say 25 ml each) to determine how long it takes for the deep blue colour to develop.
- For procedure A pour some of each solution into flasks marked X and Y, or
- For procedure B pour some (about 1/4 full) solution X and Y into each pair of test tubes.
- Except for one set dilute each of the other sets to a varying degree with water
- Pour only water into one pair.

What You Do During the Show:
A - Mix the two solutions into one of the flasks and mentally keep track of the time. At the appropriate moment (see patter) point to the flask as the colour changes.
B - Have the volunteers mix their solutions at the same time. Raise the hand of the eventual winner (see patter).

What is Happening:
There is a stepwise series of reactions. Some of the iodate ion is reduced to iodide ion, which reacts with remaining iodate in the presence of acid to produce elemental iodine. The iodine then reacts with starch to produce a blue-black complex. The rate of the reaction is dependent upon concentration of reactants; diluting stock solutions results in a longer reaction time.

Hazards:
- sulfuric acid is extrememly corrosive. Handle while wearing protective equipment (gloves and lab coat).
- use wide mouth test tubes so that the volunteers (probably non-chemists) can safely pour solution X into Y (or Y into X) and mix without spilling.

Patter:
A - The Wizard has been asked to develop a test to see which magic phrase works best when performing a trick. Ask the audience for some to test. Mix solutions X and Y. Then have the audience say one of the phrases and point to the flask. Nothing happens. Try several more phrases. It is important that you keep track of the exact time, for you will want to point at the flask exactly as it turns coloured. Note that if you make up the stock solutions elsewhere and transport to the performance (e.g. in the trunk of a car in winter), make sure the reagents are at the same temperature as where you tested the timing - this reaction is also temperature sensitive.
B - The Wizard has been asked to develop a test to see who is the happiest. The volunteers will all mix solutions and all but one will eventually give a blue colour. Congratulate the winner and ask for applause as you lift the arm of the one who had NO blue colour. Everyone will expect the winner to be the one with the first blue colour. Explain that this was a test for happiness.
The winner was the most un-blue.