New Job for Pores

An entirely new method of filtering gases and liquids---a simple, cheap, quick way to separate air from water, water from oil, etc.--was announced last week by Selas Co., a Philadelphia engineering firm that has fathered many another useful recent invention.* Its industrial possibilities are so far-reaching that the discovery may prove as significant as invention of the sieve, the basis of all mechanical filters.

Its discoverer is a young Selas physical chemist named John M. Walker. He has astonished engineers with some of his demonstrations: e.g., he pours a mixture of kerosene and water into a tube; the liquid comes out rapidly through the pores of two closed-end porcelain cylinders which are the outlets of the vessel; out of one comes pure water, out of the other, pure kerosene (see cut).

Projection from a Needle. Walker's discovery is an ingenious projection of a phenomenon familiar to every schoolboy: a dry needle laid on water will float because of the water's surface tension. Surface tension is what makes water stick to the sides of a glass, and if a column of glass is fine enough, water will actually climb up its sides. Suppose, reasoned Walker, this "wetting" principle were applied to a porous membrane: would water filling the pores have enough surface (or "interfacial") tension to block other liquids while letting water through?

Walker tested his theory on fine porcelain membranes with pores as small as a 25,000th of an inch. It worked. By treating porcelain so that it could be wetted only by a specified liquid (e.g., coated with a special stearate, porcelain is wetted by kerosene but not by water), he found that up to a certain pressure the membrane was porous to that liquid but not to others.

Thus he eventually developed membranes that speedily separated not only water from oil but various liquid chemicals from water, water from city gas, water from compressed air. (His method separates only immiscible fluids and gases, does not work on emulsions or solutions.)

Projection of a Future. Selas Co. believes Chemist Walker's discovery is a fundamentally new principle of filtration, basically different from the two previously known: i.e., mechanical filters (like the sieve) and osmosis (which operates through membranes fine enough to separate molecules).

Because it is much simpler and less expensive than methods now used industrially to separate liquids and gases (e.g., whirling, absorbing, distilling), it has immense industrial possibilities. One application Walker has already suggested to engineers: eliminating water from aviation gasoline.

But Walker believes his finding has more than industrial significance. He thinks, for example, that it may explain a phenomenon which has long puzzled physiologists: why it is that oxygen can pass from the lung into the blood, but blood cannot enter the lung. Walker's theory: blood vessels in the walls of the lung are porous membranes coated with fatty substances that are not wetted by blood, therefore they block blood but let gases pass freely.

* E.g., equipment which made possible the flash-drying of ink for high-speed printing; compact heating units for high-altitude bombers.

This file is automatically generated by a robot program, so reader's discretion is required.