562 PHYSIOLOGICAL CHEMISTRY 



the aid of a little water to a platinum dish and evaporate to dryness over a free 

 flame. (The alkalies are in the form of sulphate and do not volatilize.) Dissolve 

 the residue in hot water with the aid of a little dilute hydrochloric acid. Heat to 

 boiling and add barium chloride solution until no more precipitate forms. While 

 still hot add an excess of ammonia and ammonium carbonate. The barium chlor- 

 ide precipitates the sulphates and part of the phosphates: the ammonia in the 

 presence of excess barium precipitates the rest of the phosphates, and the carbonate 

 precipitates the calcium and most of the magnesium, as well as the excess barium. 

 Filter and wash the precipitate well with hot water containing a few drops of am- 

 monia. Evaporate nitrate and washings to dryness and heat the residue to dull 

 redness for a moment. Redissolve in water and treat again with ammonia and 

 ammonium carbonate to remove any remaining alkaline earth metals. Filter and 

 wash as before. Transfer nitrate and washings to a weighed platinum dish, add a 

 few drops of hydrochloric acid and evaporate to dryness. Heat the residue gently 

 to remove ammonium salts and then to dull redness for a moment. Desiccate 

 and weigh. Reheat to constant weight which represents the combined chlorides 

 of sodium and potassium. The reagents used in the determination must be tested 

 and found free from alkali metals or a correction made for the alkali metals present 

 in the reagents used. The sodium is determined by difference after potassium has 

 been estimated by the method given below. 



Potassium. Dissolve the alkali chlorides from the preceding determination in a 

 little water and add a slight excess of 10 per cent platinic chloride over that neces- 

 sary to precipitate all of the alkali present calculated as sodium chloride (about 1 7 

 c.c. being required for each gram of sodium chloride). Evaporate to a syrupy con- 

 sistency on the water-bath and add about 50 c.c. of 80 per cent alcohol. Stir 

 occasionally for a few minutes. This operation must be carried out in the absence of 

 ammonia vapors. Filter through a weighed Gooch crucible, washing the precipi- 

 tate with 80 per cent alcohol first thoroughly by decantation and then on the filter, 

 for some time after the filtrate is colorless. Dry at no-ii5C. and weigh. 



Calculation. Multiply the weight of potassium platinic chloride by 0.1941 to 

 obtain the amount of K 2 O present. Express as KC1 by using instead of this factor 

 the factor 0.307 12. Subtract from the weight of total alkali chlorides as determined 

 in the preceding method, the weight of potassium chloride as calculated and obtain 

 the amount of sodium chloride present. 



Interpretation. The average alkali excretion of an adult on a mixed diet is about 

 2-3 grams of potassium expressed as K 2 and 4-6 grams of sodium expressed as 

 Na 2 O. The ratio of Na to K is thus about 5:3. Both the ratio and the absolute 

 amounts of these elements excreted are, however, largely dependent upon the salt 

 content of the diet. Because of the non-ingestion of sodium chloride and the 

 accompanying destruction of potassium-containing body tissues, the urine during 

 fasting contains more potassium than sodium salts. The excretion of the bases, 

 particularly K, may be increased in fevers and in acidosis. 



Iron 



Method of Wolter. 1 Principle. The urine is ashed, the ash dissolved, and the 

 iron present oxidized to the ferric form by means of hydrogen peroxide. The iron is 

 then determined iodometrically. 



1 Wolter: Bioch. Zeit., 24, 108, 1910. 



