The standard PP units with glass cylinder are suitable for aqueous liquids, dilute acids and alkalis - not for use with solvents and hydrofluoric acid which attack PP (for bottles with GL 32 thread). The glass cylinder and PTFE encased glass piston with PP body models are designed for aqueous solutions, weakly concentrated acids, alkaline solutions and crystallising liquids compatible with PP. The amber glass cylinders, clear glass piston with PP body are suitable for light-sensitive liquids, compatible with PP.