Axial Port Research Articles

A density gradient fractionator

A density gradient fractionator sometimes referred to as a pycnograph has a chamber to receive a volume of the gradient, light density end uppermost and a volume of a sample as a surface layer so that its particulate contents that will settle therefrom in response to the earth''s gravity can sediment into the gradient. The fractionator has piston means reciprocable in the chamber and having a discharge tube connected thereto with its lower end extending through and slidably sealed in the bottom of the chamber and with its upper end open to function as an overflow for the chamber so that as the piston means is advanced, the gradient and its sedimented zones are forced into the discharge tube, light density end first. The piston means includes a piston with an upper chamber for the sample provided by a recess in its upper surface, the piston having an axial port and the piston means including a valve in control of the port and connected to the piston for movement relative thereto for a short distance to provide opened and closed positions, movement of the valve thereafter resulting in movement of the piston in a corresponding direction. Means are provided to stir the gradient in a transverse plane in any zone in which particles may be trapped against settling or rising to the level in the gradient equal to their density.