The most important unsolved problems of the Kjeldahl method for total nitrogen are concerned with digestion conditions. The quantity of sulfuric acid used in comparison to the size of sample, and the amount of added salt, are factors of importance. Addition of extra sulfuric acid during digestion is often desirable. Mercury is the most effective catalyst for digestion of proteins and usually cannot be satisfactorily replaced by selenium, which must be kept under constant control. Oxidizing agents, except hydrogen peroxide, should be

ANY discoveries of far-reaching importance have been fundamentally extremely simple. The discovery that boiling many nitrogen-containing organic compounds in concentrated sulfuric acid liberates the nitrogen in the form of ammonium sulfate is probably one of the most significant analytical discoveries ever made. Attributed to Kjeldahl,! Tho announced the method in 1883, this method has probably been applied in one modification or another to every possible form of nitrogen, and in perhaps more laboratories than almost any other single type of analytical method.