492 THE INORGANIC CONSTITUENTS OF THE URINE. 



three-quarters of an hour's warming upon the water-bath, the precipitate will 

 have been deposited. This is collected upon an ash-free filter, first washed out 

 with water, then with warm dilute hydrochloric acid, and finally again with water. 

 The barium sulphate thus purified is fused and weighed. It contains all of the 

 sulphuric acid united with salts. The filtrate and the wash-water contain besides 

 the conjugate sulphates. The combined fluid is mixed with one-eighth of its 

 volume of concentrated hydrochloric acid and heated for a considerable time. 

 Barium sulphate and a resinous mass separate out. The fluid is filtered, and 

 the resinous mass is dissolved and washed from the filter with hot alcohol, and 

 finally, again washed with hot water, then dried and fused. One part of barium 

 sulphate corresponds to 0.3433 sulphuric acid. 



In addition to sulphuric acid, sulphur (one-fifth) occurs in the urine in an 

 incompletely oxidized form (potassium sulphocyanate, cystin, and a sulphurous 

 substance derived from the bile). Sulphurous acid, constant in carnivora, occurs 

 in normal human urine only when hydrogen sulphid is formed in the intestine 

 in considerable amount. Hydrogen sulphid, which is less commonly observed, 

 is abnormal. It is recognizable by the black discoloration of paper moistened 

 with lead acetate and ammonia when held over the urine. It results principally 

 through fermentation by bacteria (bacterium coli) , and is rarely absorbed from 

 the intestine or from pathological putrid foci. 



Small amounts of silicic acid and nitric acid, derived from drinking- 

 water, the latter, however, in part produced in the body itself, are 

 present. In the fermentation of urine, the nitrates are reduced to 

 nitrites. After the administration of salts of the vegetable acids, car- 

 bonates appear in the urine, which then effervesces upon addition of 

 an acid. 



Sodium in the urine is principally united with chlorin, and in lesser 

 degree with phosphoric acid and uric acid. Potassium, equaling about 

 one-third of the sodium, is combined principally with chlorin. During 

 fever, more potassium is excreted than sodium, while the reverse occurs 

 during convalescence. Calcium and magnesium are present in normal 

 acid urine dissolved as chlorids or acid phosphates. If the urine be- 

 comes neutral, neutral calcium phosphate and magnesium phosphate 

 are precipitated. The latter has been found also in alkaline urine in 

 association with disorders of the stomach, in the form of large, trans- 

 parent, four-sided prisms. If the urine becomes alkaline, calcium car- 

 bonate (Fig. 172, a), or amorphous tribasic calcium phosphate is pre- 

 cipitated, the magnesium, however, in the form of ammonio-magnesium 

 phosphate (triple phosphate). The calcium is derived from food, and 

 its amount varies in accordance with the digestive and absorptive 

 capability of the digestive tract. In the presence of pulmonary tuber- 

 culosis and diabetes, the excretion of calcium is increased. 



Free ammonia, from 0.06 to 0.88 gram in the day, occurs also in 

 quite fresh urine, and in larger amount with animal than with vegetable 

 food. After administration of mineral acids, the excretion of com- 

 bined ammonia likewise increases. The appearance of an increased 

 amount of ammonia indicates a predominance of acids in the body and a 

 deficiency of alkalies. Demonstration: A strip of red litmus-paper held 

 over a mixture of urine and milk of lime in a covered glass becomes 

 blue. The alkaline combinations of the organic acids diminish the 

 excretion of ammonia. Inorganic ammonia-combinations are trans- 

 formed into organic combinations, perhaps into an ammonium albu- 

 minate. 



Iron is never wanting in the urine, from 2.5 to 10 mg. being excreted 

 daily. Further, some hydrogen dioxid is present, and is recognized 

 by discoloration of a solution of indigo on addition of an iron sulphate. 



