A dispenser is disclosed which releases a substance such as chlorine into an aqueous solution such as the water of a swimming pool. The dispenser includes a bag or sachet which has a liquid permeable wall. The chlorine or other soluble material within the bag or sachet is dissolved or subjected to a leaching action in the liquid. In this manner the material is released into the liquid. The dispenser contains both a buoyant material and weighting material. The overall weight of the dispenser is such that it is immersed when initially deposited into the liquid and is buoyant in the liquid when the reactive material has dissolved.
