3O2 PHYSIOLOGICAL CHEMISTRY. 



amine the crystalline sediment under the microscope and compare 

 the forms of the crystals with those shown in Fig. 96, page 301. 



2. " Triple Phosphate " Crystals in Amrnoniacal Fe.rmenta- 

 tion. Stand some urine aside in a beaker for several days. Am- 

 moniacal fermentation will develop and " triple phosphate " crystals 

 will form. Examine the sediment under the microscope and com- 

 pare the crystals with those shown in Fig. 96, p. 301. 



3. Detection of Earthy Phosphates. Place 10 c.c. of urine 

 in a test-tube and render it alkaline with ammonium hydroxide. 

 Warm the mixture and note the separation of a precipitate of earthy 

 phosphates. 



4. Detection of Alkaline Phosphates. Filter off the earthy 

 phosphates as formed in the last experiment, and add a small amount 

 of magnesia mixture (see page 295) to the nitrate. Now warm 

 the mixture and observe the formation of a white precipitate due 

 to the presence of alkaline phosphates. Note the difference in the 

 size of the precipitates of the two forms of phosphates from this 

 same volume of urine. Which form of phosphates were present 

 in the larger amount, earthy or alkaline? 



5. Influence upon Fehling's Solution. Place 2 c.c. of Feh- 

 ling's solution in a test-tube, dilute it with 4 volumes of water and 

 heat to boiling. Add a solution of sodium dihydrogen phosphate, 

 NaH 2 PO 4 , a small amount at a time, and heat after each addition. 

 What do you observe? What does this observation force you to 

 conclude regarding the interference of phosphates in the testing of 

 diabetic urine by means of Fehling's test? 



Sodium and Potassium. 



The elements sodium and potassium are always present in the 

 urine. . Usually they are combined with such acidic radicals as 

 Cl, CO 3 , SO 4 and PO 4 . The amount of potassium, expressed as 

 K 2 O, excreted in 24 hours by an adult, subsisting upon a mixed 

 diet, is on the average 2-3 grams, whereas the amount of sodium, 

 expressed as Na 2 O, under the same conditions, is ordinarily 4-6 

 grams. The ratio of K to Na is generally about 3:5. The ab- 

 solute quantity of these elements excreted, depends, of course, in 

 large measure, upon the nature of the diet. Because of the non- 

 ingestion of NaCl and the accompanying destruction of potassium- 

 containing body tissues, the urine during fasting contains more 

 potassium salts than sodium salts. 



Pathologically the output of potassium, in its relation to sodium, 



