Perfume compositions and method of formulating perfume compositions designed for use in rinse-off or high dilution systems provide a sustained linear release andor a delayed release, with the odorants selected according to their mass transfer values, odor detection thresholds andor calculated odor indices. The image sensing device detects an image from a selected region of a user of the hearing aid while the sound input transducer receives sound and produces an audio signal representative of the sound. The plant further contains a reactor system with several stages for removing carbon monoxide from the reformate gas stream.