In the following video we see as a basic solution of methylene blue discolored in seconds by adding glucose, which acts as a reducer. However, to stir the dissolution the bluish color returns to recover because the reduced form is oxidized again to blue methylene with atmospheric oxygen.
When the dissolution remains without agitation for a few seconds the dissolved oxygen it is consumed quickly and glucose reduces to the colorless form methylene blue. It is enough to stir a few seconds so the oxygen dissolves and again to look like the color blue due to oxidized form.
Department of Inorganic Chemistry
Universidad de Alicante Carretera de San Vicente del Raspeig s/n 03690 San Vicente del Raspeig Alicante (Spain)