(Borosilicate glass 3.3) Vigreux columns with silver - coated high vacuum jacket (10-7 mbar) with expansion bellows and sight strip. Vigreux columns are occasionally still in use these days. Especially during distillations at a higher vacuum the infinitesimal differential pressure between boiling flask and column head becomes apparent. The exchange of liquid phase and vapour phase takes place at the inner wall of the column which is enlarged through glass notches. These notches have to be packed as tightly as possible. Spatial dislocations help avoiding the formation of liquid and vapour channels. The number of theoretical plates and hence the separation efficiency is comparatively low.