To prevent leakage of {HEAD ~ gas} from within the cell the substrates have sealing areas 24 at opposite edges to cooperate with the sealing surfaces on {TAIL ~ the plates} 
To prevent leakage of { HEAD ~ gas } from within the cell the substrates have sealing areas 24 at opposite edges to cooperate with the sealing surfaces on { TAIL ~ the plates }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL