Page "Gas mask" Paragraph 19

This principle relies on the fact that substances which can do harm to humans are usually more reactive than air.

This method of separation will use some form of generally reactive substance ( for example an acid ) coating or supported by some solid material.

An example is synthetic resins.

These can be created with different groups of atoms ( usually called functional groups ) that exhibit different properties.

Thus a resin can be tailored to a particular toxic group.

When the reactive substance comes in contact with the resin, it will bond to it, removing it from the air stream.

It may also exchange with a less harmful substance at this site.