Attached to the hole in the side there is a vacuum which sucks the air out of the BÃ 1\/4 chner flask . A vacuum tight seal and stability of the BÃ 1\/4 chner flask and filter are essential during the filtration process . A BÃ 1\/4 chner ring can be used with BÃ 1\/4 chner funnels , flasks , glass crucibles and gooch crucibles .