424 PHYSIOLOGICAL CHEMISTRY 



of the blood when the latter is decreased in the manner above stated. 

 When this substitution is attempted the potassium salt is excreted at 

 once in the urine, and death follows as above indicated. 



Pathologically the excretion of chlorides may be decreased in some 

 fevers, chronic nephritis, croupous pneumonia, diarrhoea, certain stom- 

 ach disorders, and in acute articular rheumatism. Any condition ac- 

 companied by the formation of an exudate (e.g., pneumonia) will cause 

 a diminished chloride output. In convalescence and with resolution 

 of the exudate the chloride excretion rises again. 



EXPERIMENT 



Detection of Chlorides in Urine. Place about 5 c.c. of urine in a test-tube, 

 render it acid with nitric acid and add a few drops of a solution of silver nitrate. 

 A white precipitate, due to the formation of silver chloride, is produced. This 

 precipitate is soluble in ammonium hydroxide. 



Phosphates 



Phosphoric acid exists in the urine in two general forms: First, 

 that in combination with the alkali metals, sodium and potassium, 

 and the radical ammonium; second, that in combination with the 

 alkaline earth metals, calcium and magnesium. Phosphates formed 

 through a union of phosphoric acid with the alkali metals are termed 

 alkaline phosphates, or phosphates of the alkali metals, whereas phos- 

 phates formed through a union of phosphoric acid with the alkaline 

 earth metals are termed earthy phosphates or phosphates of the alkaline 

 earth metals. 



Three series of salts are formed by phosphoric acid: Normal, 

 MsPOi, 1 mono-hydrogen, M 2 HP04, and di-hydrogen, MH 2 PO4. The di- 

 hydrogen salts are acid in reaction, and it is claimed that about 60 per 

 cent of the total phosphate content of the urine is in the form of this 

 type of salt, and that the acidity of the urine is due in great part to the 

 presence of sodium di-hydrogen phosphate (see page 378). Henderson 2 

 maintains that " determinations of hydrogen ionization in urine and its 

 behavior toward indicators both support the view that in urine there 

 exists a mixture of mono- and di-hydrogen phosphates of sodium, 

 ammonium and other bases." 



In bones" the phosphates occur principally in the form of the normal 

 salts of calcium and magnesium. The mono-hydrogen salts as a class 

 are alkaline in reaction to litmus, and it is to the presence of di-sodium 



1 M may be occupied by any of the alkali metals or alkaline earth metals. 



2 Henderson: Am. Jour. Physiol., 15, 257, 1906. 



