_Procedure._—To 50 cc. of the sample to be tested, diluted if necessary with an equal volume of ammonia-free water, in a short tube, add a few drops of the copper sulfate solution. After thoroughly mixing, add 1 cc. of the alkali hydroxide solution and again thoroughly mix. Allow the tube to stand for a few minutes, when a heavy precipitate should fall to the bottom, leaving a colorless supernatant liquid. Nesslerize an aliquot part. Compare with standards and compute the ammonia nitrogen in the same manner as in the distillation procedure. Samples containing hydrogen sulfide may require the use of lead acetate in addition to the copper sulfate. Some samples may require a few trials before the right combination of the three solutions to bring about the best results can be found. Instead of adding copper sulfate to sewages of high magnesium content satisfactory clarification of the sample can be obtained by mixing it with the alkali hydroxide alone.[54] ALBUMINOID NITROGEN. The addition of an alkaline permanganate solution to liquids containing nitrogenous organic matter causes the formation of ammonia, which can be distilled and determined by Nesslerization of the distillate. The nitrogen of the ammonia, thus obtained, is called albuminoid nitrogen. As the ratio of nitrogenous organic matter to the ammonia obtained by distillation is decidedly variable[6][30][75] in sewages and other substances containing much nitrogenous organic matter albuminoid nitrogen results on such substances are less accurate[29] than organic (Kjeldahl) nitrogen. Therefore in sewage work, including analysis of influents and effluents of purification plants and the water of highly polluted streams, it is recommended that determinations of organic nitrogen be substituted for determinations of albuminoid nitrogen. For ground waters and surface waters containing but little pollution, the albuminoid nitrogen is approximately one-half the organic nitrogen; accordingly the continuance of albuminoid nitrogen determinations for this class of work is approved. _Reagents._—Alkaline potassium permanganate. Pour 1,200 cc. of distilled water into a porcelain dish holding 2,500 cc., boil 10 minutes, and turn off the gas. Add 16 grams of C. P. potassium permanganate and stir until solution is complete. Then add 800 cc. of 50 per cent clarified solution of potassium hydroxide or an equivalent amount of sodium hydroxide and enough distilled water to fill the dish. Boil down to 2,000 cc. Test this solution for ammonia by making a blank determination. Correct determinations by the amount of this blank.