A Kjeldahl flask is a type of laboratory flask used in the Kjeldahl method for determining the nitrogen content in organic compounds. The Kjeldahl method is a widely used procedure for analyzing the nitrogen content of food, feed, and other organic substances.

The Kjeldahl flask is typically made of borosilicate glass and has a cylindrical shape with a flat bottom, a narrow neck, and a spherical or bulbous distension near the top of the neck. The distension is designed to hold a boiling stone, which provides a surface for the organic material to be decomposed and facilitates the release of nitrogen gas.

The flask is designed to be used with a condenser, which helps to cool and condense the gases produced during the reaction. The Kjeldahl flask is an essential component of the Kjeldahl method and is used to perform the crucial steps of digestion and distillation of the sample.