A BÃ 1\/4 chner flask ( also called a vacuum flask , a filter flask , a side-arm flask or a kitasato flask ) is a flask made of glass . A BÃ 1\/4 chner flask , also known as a vacuum flask , filter flask , side-arm flask or Kitasato flask , is a thick-walled Erlenmeyer flask with a short glass tube and hose barb protruding about an inch from its neck .