The Bluebottle

Materials

8g of potassium hydroxide or 6g of sodium hydroxide, 10g of glucose (dextrose), 0.05g of methylene blue, 50cm³ of ethanol.

Procedure

Make a solution of 0.05g of methylene blue in 50cm³ ethanol (0.1%). Weigh 8g of potassium hydroxide or 6g of sodium hydroxide into a 1cm³ conical flask. Add 300cm³ of water and 10g of glucose and swirl until the solids are dissolved. Add 5cm³ of the methylene blue solution. None of the quantities is critical. The resulting blue solution will turn colourless after about one minute. Stopper the flask.

Shake the flask vigorously so that air dissolves in the solution. The colour will change to blue. This will fade back to colourless over about 30 seconds. The more shaking, the longer the blue colour will take to fade. The process can be repeated for over 20 cycles. After some hours, the solution will turn yellow and the colour changes will fail to occur

The Chemistry

Glucose is a reducing agent and in alkaline solution will reduce methylene blue to a colourless form. Shaking the solution admits oxygen which will re-oxidise the methylene blue back to the blue form.

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