(2) _Potassium Permanganate._—Crystals of this salt are crushed (not pulverized) with a pestle into small pieces of about one-half millimeter size, which are kept in a long glass tube of about ten millimeters diameter, closed with a stopper. (3) _Ammonia-free Water._—Common distilled water cannot be used in the determination of nitrogen according to Kjeldahl, since it contains ammonia. It may be obtained free from the same by redistillation in a large glass retort with the addition of a few drops of sulfuric acid. All vessels used in the determination are rinsed out beforehand with this water. (4) _Ammonia-free Soda-lye_ is most conveniently prepared by adding 270 grams of common sodium hydroxid in sticks, little by little, to one liter of distilled water which is kept continually boiling, by means of a small flame, in a good-sized silver dish. The dish is kept covered with a glass plate. Care has to be exercised not to add the alkali too rapidly, nor in too large quantities at a time for in this case the fluid will boil too violently at every addition of the alkali. After the operation is finished the lye is at once siphoned into a glass flask, and when cold, is poured into a glass-stoppered bottle. (5) _One-twentieth Normal Sulfuric Acid_ is prepared from sulfuric acid and water both absolutely ammonia-free, and is kept in a place where no fumes of ammonia can reach it, in a well-stoppered glass bottle, the stopper being smeared with vaseline. (6) _Sodium Thiosulfate Solution._—This should be of the same strength as the one-twentieth normal sulfuric acid. It is prepared by dissolving the salt in ammonia-free water, and is compared with the acid, to which has been added potassium iodid and iodate, using starch as an indicator, in the manner described above. The solution is kept in a well-stoppered bottle, in the dark. When the salt and water used are perfectly pure, it will keep unchanged for a long time. (7) _Potassium Iodid._—Dissolve five grams of chemically pure potassium iodid in ammonia-free water and make the volume 100 cubic centimeters. Ten cubic centimeters of this solution are used for each determination; keep the solution in the dark and in a well-stoppered bottle. (8) _Potassium Iodate._—Dissolve four grams of chemically pure potassium iodate in ammonia-free water and make the volume 100 cubic centimeters. Use two cubic centimeters of this solution for each determination. (9) _Starch Solution._—Digest pure starch for about a week with dilute hydrochloric acid, wash perfectly free from chlorin by decantation, and finally dry it between filter-paper. The starch is then dissolved in water with the aid of heat. Such a solution will keep for an indefinite time, if it be saturated with common salt. Ten grams of this starch are dissolved in 1,000 cubic centimeters of ammonia-free water; use one or two cubic centimeters for each determination.