Then the amount of N will be 150∕100 × 5∕25 = ·3 parts per 100,000. If the two solutions (_a_) and (_b_) when diluted have the same tint, then the Amount of N in the sample = 5∕25 = ·2 parts per 100,000. (6) =Determination of Organic Matter.= Frankland’s =combustion process= involves the use of delicate and costly apparatus, and is seldom employed. In this process the organic carbon is evolved as carbonic acid, and the nitrogen as such. =Wanklyn’s ammonia process= is based on the reduction of organic matter to ammonia. Part of this ammonia, =free or saline ammonia=, is simply combined with carbonic, nitric, or other acids, or is easily derived from the urea of urine, CH₄N₂O + 2H₂O = 2(NH₄)₂CO₃. Another part is only set free when the water is boiled with a strongly alkaline solution of permanganate of potassium. This is called the =albuminoid ammonia=. In carrying out this method, a retort is taken, and after having been washed out, first with a little sulphuric acid, and then with some of the water to be analysed, 500 c.c. of the latter is put in, and the retort is connected with a condenser, and distillation begun; 50 c.c. of the distilled water is collected in a cylindrical glass tube called a Nessler glass. To this 1½ c.c. of Nessler’s reagent (mercuric iodide dissolved in a solution of potassic iodide and made alkaline by potass) are added. A rich brown colour is produced, if any ammonia is present in the distillate. The amount of ammonia in the distillate is determined by exactly imitating its colour by adding a known quantity of a standard solution of ammonium-chloride to 50 c.c. of ammonia-free distilled water, and then Nesslerising as before. Each c.c. of the dilute standard ammonium chloride solution is equivalent to ·00001 gramme of ammonia (NH₃). If the first 50 c.c. of water distilled over gives only a slight colouration with the Nessler solution, no more water needs to be distilled over for free ammonia. If more is present, two more 50 c.c.’s must be distilled over, and the amounts of the standard solution required for imitating the test in each Nesslerised 50 c.c. added together. Thus, if 2 c.c. were needed. This = ·00002 grm. NH₃, which is contained in 500 c.c. of the water = ·00002 × 200 = ·004 parts saline NH₃ in 100,000 of water.