Of all the common laboratory test methods the Kjeldahl method for determining nitrogen subjects the boiling flask to the most severe thermal and chemical abuse. These Kjeldahl flasks specially styled have tooled finished necks for extra strength and uniform stopper fit. Wall thickness is controlled to offer the optimum balance between thermal shock and chemical resistance. Can be used in ASTM E258 procedure. Care must be taken to ensure the bottoms of the flasks do not come in contact with the heating elements. Most Kjeldahl equipment manufacturers have ring supports for this purpose.