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The effect of temperature on the rate of Kjeldahl digestions in the absence of catalyst and oxidizing agent has been studied. Both the clearing time and the minimum time for complete recovery of nitrogen are markedly decreased by raising the digestion temperature. The appreciable rise in temperature during prolonged digestions and the effect of time and temperature on the pyrolytic loss of nitrogen are considered. By proper choice of digestion conditions nitrogen can be completely recovered in a reasonable time even from refractory compounds. The time may be further decreased by the use of mercury as catalyst. The use of hydrogen peroxide as an oxidant in Kjeldahl digestions is discussed and the effects of the volume and number of additions at various temperatures after different cooling times determined. Earlier claims regarding complete recoveries with few additions cannot be substantiated. A modified micro-apparatus for the distillation of ammonia from Kjeldahl digestions is described and acidimetric methods for the determination of the ammonia are critically examined. As a result of this work it is possible to develop procedures for the Kjeldahl determination of nitrogen in various materials. A rapid and precise method for the determination of 0.2-2 mg of nitrogen in amino acids and proteins is described.
McKenzie et al. (Mon,) studied this question.