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