In operation a molten glass layer, {HEAD ~ a molten layer} of {TAIL ~ undissolved sulfates}, and a batch layer succeed one another from the bottom up in the melting section 
In operation a molten glass layer , { HEAD ~ a molten layer } of { TAIL ~ undissolved sulfates } , and a batch layer succeed one another from the bottom up in the melting section
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH