Unlike the other hydrogen halides, HF is lighter than air and diffuses relatively quickly through porous substances.

Note that special care has to be taken in measuring porous substances such as fabrics as some techniques are not appropriate.

So far, much of the molecular engineering of catalysts in the petroleum industry has focused on zeolite, a porous substance found in volcanic rocks.

It's actually a black porous substance made by heating coal in the absence of air, and consists of virtually pure carbon.

Both ceiling and wall were, for as far as he could see, of some white, porous substance, almost, but not quite, like bone.

We will accept that you are selling coke if the solid fuel is a light porous substance of the residue of coal, lignite or peat.

Networks defined in fracture systems and porous substances have demonstrated these characteristics.

Given time, they pass easily through porous substances.

A different trial is underway for a patch made of a porous substance on to which the stem cells are "seeded" in order to induce tissue regeneration in heart defects.

When the silo is filled or the stack built, a layer of straw or some other dry porous substance may be spread over the surface.