The alkali metal cations then accept {HEAD ~ electrons} from electrode 18 and return to {TAIL ~ their elemental state} 
The alkali metal cations then accept { HEAD ~ electrons } from electrode 18 and return to { TAIL ~ their elemental state }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL