When a Constricted Internal Diameter is About to Close Off

摘要

Perhaps you have had the i.d. of a side arm or stopcock start to constrict while it is being sealed to a larger diameter tube or flask. This happens more often when re-using old parts and when the sidearm is attached at a sharp angle to the main body (see sketch 1). Once the glass has thickened too much, it seems that no combination of blowing and gravity can get it to thin back out to a reasonable wall weight. The surface tension in the thickened area will continue to draw more glass into itself until the inner diameter has completely closed. Now you are left with cutting off the offending piece and starting over.