AbstractA discussion is given of the design of tubes for precision micropolarimetry, which involves the consideration of sources of error negligible in ordinary tubes. A micro‐tube has been developed which is adapted to the conventional polarizer and analyser. Special provision has been made for easy filling and recovery of solution, accurate temperature control, and rapid temperature changes. The design minimizes errors due to optical and manipulative causes. Comparison with other polarimeters described in the literature shows that the precision is equal to that of good macro‐tubes and better than most micro‐tubes. The range of conditions over which Useful data can be obtained is substantially wider than with previously described micro‐tubes.