A method of providing in an atmosphere both a continual supply of volatile liquid and the possibility for a time of an enhanced supply, comprising providing the liquid (3) in a reservoir (1) with an opening, which opening is covered by a membrane (4) of a thickness of from 0.05-0.4 mm so as to define within the reservoir an internal evaporation space (6), the continual supply being provided by liquid evaporating within the internal evaporation space and passing through the membrane, and the enhanced supply being provided by evaporation from liquid absorbed in the membrane which has been brought into contact with the liquid and then separated therefrom. The method is easily carried out with a simple, cheap device. A suitable choice of membrane also gives an end-of-life indication by changing colour as liquid absorbed therein is disseminated.
