Abstract
The Wilhelmi hanging-plate technic was adopted to the study of unimolecular films at liquid-liquid interfaces in the low pressure region. Details of the apparatus are given. Applying the laws for a 2 -dimensional gas to the results obtained with human methemoglobin and bovine serum albumin at the benzene-water interface at pH 6.8, it is concluded that the molecule of human methemoglobin dissociates into 8, and bovine serum albumin into 16 kinetic units under these conditions.