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 the interior and the exterior of {TAIL ~ the chamber} 
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 the interior and the exterior of { TAIL ~ 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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL