A magnesium bed of mixed magnesium turnings and a resulting considerably broader particle size distribution corresponds more to a changing magnesium bed during an ongoing Grignard reagent synthesis. For a mixture of fine magnesium turnings (75 %) and coarse magnesium turnings (25 %), the void fraction ε was 0.52 and the magnesium mass was 26 g. This is close to the bed porosity of a magnesium bed of exclusively fine turnings due to the higher density of fine magnesium turnings. A larger fraction of fine turnings was used because during an ongoing synthesis the average size of the magnesium turnings in the reactor shifts to smaller sizes and only the magnesium turnings replenished by means of the replenishing unit have their original size.