Identification of a previously undetected source of systematic error in capillary viscometry measurements.

A new analysis of the factors affecting the driving head within a capillary viscometer has identified a previously undetected source of error due to surface tension. In contrast to the well-known capillary rise correction to the effective driving head, this additional effect requires that a correction be made to the apparent head of liquid. Calculations show that this source of error may be responsible for deviations in experimental results as large as 1%. A new calibration equation which compensates for both surface tension effects is recommended.