A mixture is described which comprises or consists of one or more compounds of formula : and one or more compounds of formula : in which R has the same meaning or a different meaning in formula and formula and is selected in each case from the group consisting of methyl and ethyl, and optionally one, two or more other fragrances or flavourings. The system comprises a main unit housing an iodidewater sample chamber and a reducing agent chamber. The SiH4-oxide has hydrogen constituents removed by displacement to prevent an amorphous material layer from being formed on the insulating interlayer. The top rail has a pair of friction devices mounted thereon and the handle has a stem attached to the top rail between the friction devices.