The apparatus consists of a metal bridge 130 x 90 x 80 mm,
fitted with anti-slip rubber edging strips. The air-cell holder
is attached to a large knob and scale, Graduated 0-360 . The
air-cell takes the form of two flat glass plates, 50 x 50
mm, arranged parallel and at a small distance apart in a sealed
masking frame. Liquid under investigation is contained in
a transparent perspex tank. WITH tank.