An apparatus adapted to disseminate a volatile liquid, such as a fragrance, an insecticide or a fungicide, into an atmosphere, the apparatus comprising a reservoir containing the liquid and a porous transfer member through which the liquid is conveyed from the reservoir to the atmosphere, the apparatus additionally comprising means of pressure equalization between atmosphere and reservoir, which means is adapted to effect a pressure-equalising change in volume of the reservoir, when the apparatus is in operation. The apparatus does not suffer from the leaking problems of known apparatus of the same kind, and is especially useful in apparatus in which one of two liquids, particularly fragrances, may be singly dispensed, by the inversion of the apparatus.