The selective transmission may be achieved by providing a wall section consisting of a selectively permeable material, chosen to permit the transfer of {HEAD ~ only the gaseous substance} to be monitored between {TAIL ~ the interior} and the exterior of the chamber 
to be monitored between
The selective transmission may be achieved by providing a wall section consisting of a selectively permeable material , chosen to permit the transfer of { HEAD ~ only the gaseous substance } to be monitored between { TAIL ~ the interior } and the exterior of the chamber
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH