Heat helps the chemicals to react with the stains.

The chemicals on the old print would react with the pigmented paper, leaving behind a mirror image.

These chemicals react with moisture and bind to the clay.

There is a further constraint to the conditions, since a fire spokesman had said 'Two chemicals had reacted together'.

The chemicals in the packet reacted with the water in the bottle, which exploded.

The chemicals immediately react to one another, and the atoms begin emitting light.

Furthermore, a chemical in the glass reacted with the sun, darkening the windows so they looked filthy.

Not enough chemicals react dramatically with the modest amount of power in daylight or, 100x weaker, room light.

If you disperse it in water and put an electric current across it, the chemicals will react.

These two chemicals react with oxygen, when available, and actually generate light.