1892.] PUBLIC DOCUMENT — No. 33. 279 



centimetres of nitric acid of specific gravity 1.20, and set in 

 a warm place for several days, or until a portion heated to 

 40° C. deposits no yellow precipitate. 



The magnesia mixture is prepared by dissolving 110 

 grams of crystallized magnesium chloride and 280 grams of 

 ammonium chloride in 700 cubic centimetres of ammonia of 

 specific gravity .96, and bringing to a volume of two liters. 



2. Methods of Determining Nitrogen. — The Kjeldahl 

 and soda- lime methods recommended by the Association of 

 Official Agricultural Chemists, in their "Proceedings." 1890, 

 pages 190 and 191, are employed, with occasional control 

 analyses by the absolute cupric oxide mode. 



3. Method for Determining Potash. — Weigh out two 

 grams of the material in a platinum crucible, and char 

 thoroughly at a temperature just below red heat. Digest 

 for several hours with very dilute hydrochloric acid, on the 

 water-bath. Filter into a graduated cylinder, and make up 

 to 200 cubic centimetres. Take 50 cubic centimetres for 

 each test. Warm, and add in small quantities at a time, an 

 excess of barium hydrate. Digest for one or two hours at a 

 temperature of 70° to 90° C, filter, washing carefully, and 

 add to the filtrate a few drops of ammonium hydrate, and 

 enough ammonium carbonate to precipitate the excess of 

 barium hydrate. Filter, and bring the filtrate to dryness on 

 the water-bath in a platinum dish. Heat carefully in the 

 covered platinum dish at a temperature just below red heat, 

 until compounds of ammonia cease to come off. Take up 

 the residue in water, filtering if necessary, and add an 

 excess of platinum tetrachloride. Evaporate to dryness on 

 the water-bath, add a small quantity of 80 per cent, alcohol, 

 and allow it to stand for a few hours. Filter through a 

 Gooch crucible, washing with alcohol, dry, and weish ; or 

 filter through paper, wash as before, dry, and brush the 

 potassium platinic chloride upon a weighed watch glass, with 

 a camel's-hair brush, and weigh. If very impure, the double 

 salt is washed with the strong solution of ammonium chloride, 

 saturated with potassium platinic chloride, as recommended 

 in the " Proceedings of the Association of Official Agricult- 

 ural Chemists," 1890, page 210. 



