Liquid oxygen is attracted to a magnetic field, while liquid nitrogen is not. It is this scientific basis that leads to the possibility of extracting pure liquid oxygen through condensation, and the subject of Professor Jeff Statler's simple and inexpensive demonstration recently published in the Journal of Chemical Education, a photo of extracted liquid oxygen (taken by Professor Ryan Steele) making its way to the Journal's cover.
"This demonstration extracts liquid oxygen from a cryogenic mixture collected through condensation using a small neodymium magnet. In a simple and inexpensive procedure, small amounts of liquid oxygen can be safely collected and observed. Students directly witness the collection of this cryogenic mixture over a 30 minute time period and the subsequent immediate removal of small quantities (ca. <1 mL) of liquid oxygen as a consequence of its paramagnetic properties. Several techniques are suggested that allow the efficient handling and display of the magnet used for the extraction. Although framed here in the context of an introductory chemistry or general chemistry course, these procedures can easily be adapted to general-interest audiences or more advanced undergraduate chemistry courses."
Read the full article here.