The instrument consists of an outer cylinder, which is partly filled with oil, and an inner cylinder which slides freely in the outer cylinder. The specimen is clamped in position such that the air entrapped in the inner cylinder is found to pass though it to escape. The inner cylinder is graduated so that the time required to pass a given amount of air through the specimen can be recorded.
Smoothness test : The rate of lateral air flow between several sheets of paper depends upon the smothness or roughness of their surface. By taking the time for 50 cc. of air to escape as measured on the inner cylinder, the smoothness is measured. The test can be adapted for paper boards and other material.
Porosity test : One square inch of paper is exposed to the air pressure exerted by the inner cylinder floating in oil. The rate of air flow through the paper is its porosity. Air escapes through holes in the bottom clamping plats elastic gaskets on the adapter plate prevent leakage over the surface.
Softness tester : Four softness plugs, forced into the paper sample by the weight and lever arm, constrict the space for air escape, depending upon how deeply the plugs compress the paper. The resulting rate of air flow is a measure of the paper’s softness, or compressibility.