Sprayer with internal mixing device on dip tube

A hand held sprayer 1 has an internal bag 12 containing product to be sprayed. The sprayer features an internal mixing device 15 which may be carried on the dip tube 14,16 and contains a reagent which allows causes chemical modification of a contained liquid, before ejection from the sprayer. The bag and valve structures 12,6 provide a typical sterile sprayer arrangement in that air drawn in at valve 6 during spraying, does not contact the contained liquid due to the barrier provided by the bag 12. The reagent may be a chlorine release agent in solid form, and the liquid may be a dilute aqueous acid. The sprayer may be used in sterile cleaning applications.