The method 3 wherein {HEAD ~ the second tube} is heated to {TAIL ~ at least 400° C} 
is heated to
The method 3 wherein { HEAD ~ the second tube } is heated to { TAIL ~ at least 400 ° C }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL