_Apparatus._—(1) _Kjeldahl digestion flasks_ of hard, moderately thick, well-annealed glass: These flasks are about twenty-two centimeters long, with a round, pear-shaped bottom, having a maximum diameter of six centimeters and tapering out gradually in a long neck, which is two centimeters in diameter at the narrowest part, and flared a little at the edge. The total capacity is from 225 to 250 cubic centimeters. (2) _Distillation flasks_ of ordinary shape, of 550 cubic centimeters capacity, or preferably flasks of well-annealed glass, of the same capacity, of pear-shaped bottom, for both digestion and distillation, fitted with a rubber stopper and a bulb-tube above to prevent the possibility of sodium hydroxid being carried over mechanically during distillation: The bulbs are about three centimeters in diameter, the tubes being of the same diameter as the condenser and cut off obliquely at the lower end. This is adjusted to the tube of the condenser by a rubber tube. _Manipulation._—(1) _The Digestion._—From seven-tenths to three and five-tenths grams of the substance to be analyzed, according to its proportion of nitrogen, are brought into a digestion flask with approximately seven-tenths gram of mercuric oxid or its equivalent in metallic mercury and twenty cubic centimeters of sulfuric acid. The flask is placed in an inclined position, and heated below the boiling-point of the acid for from five to fifteen minutes or until frothing has ceased. If the mixture froth badly, a small piece of paraffin may be added to prevent it. The heat is then raised until the acid boils briskly. No further attention is required until the contents of the flask have become a clear liquid, which is colorless or at least has only a very pale straw color. The flask is then removed from the frame, held upright, and while still hot, potassium permanganate is dropped in carefully and in small quantities at a time until, after shaking, the liquid remains of a green or purple color. (2) _The distillation._—After cooling, the contents of the flask are transferred to the distilling flask with about 200 cubic centimeters of water, a few pieces of granulated zinc, pumice stone, or one-half gram of zinc dust when found necessary to keep the contents of the flask from bumping, and twenty-five cubic centimeters of potassium sulfid solution are added, shaking the flask to mix its contents. Next add fifty cubic centimeters of the soda solution, or sufficient to make the reaction strongly alkaline, pouring it down the sides of the flask so that it does not mix at once with the acid solution. Connect the flask with the condenser, mix the contents by shaking, and distil until all ammonia has passed over into the standard acid. The first 150 cubic centimeters of the distillate will generally contain all the ammonia. This operation usually requires from forty minutes to one hour and a half. The distillate is then titrated with standard alkali.