The iron and {TAIL ~ sulphur} contained in {HEAD ~ the residue} remain for the most part undissolved 
The iron and { TAIL ~ sulphur } contained in { HEAD ~ the residue } remain for the most part undissolved
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH