A floating zone refining apparatus for silicon, which can operate unattended, has been assembled to assist in the production of high purity material for research purposes. Features of this equipment are a simple mechanical drive, a switching panel to recycle the apparatus, and a self‐stabilizing rf heating circuit to maintain constant zone length. Silicon containing less than 1 part per billion of electrically active impurities (resistivity of 16 000 ohm cm and lifetime of 1.2 milliseconds) has been prepared. The effect of many‐pass refinings on the diameter of the sample is discussed. Surface tension effects on material transport are significant.