The are discharge method has been used hitherto to encapsulate metal-containing structures within carbon nanotubes [1,2], the arrangement of the nanotube walls playing an important role in the process. We show that KCl can be generated in the space between nanotube walls by treating potassium-intercalated uncapped tubes with CCl4. A relationship between the KCl crystal domain and the hexagonal carbon network is thought to give rise to preferential formation of a 100 plane perpendicular to the tube axes.