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