URINE 409 



4. Detection of Alkaline Phosphates. Filter off the earthy phosphates as 

 formed hi the last experiment, and add a small amount of magnesia mixture (see 

 page 602) to the filtrate. 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 vol- 

 ume of urine. Which form of phosphates was present in the larger amount, 

 earthy or alkaline? 



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

 betic 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, COs, SO4 

 and PO4. 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 absolute quantity of these elements excreted 

 depends, of course, in large measure upon the nature of the diet. Be- 

 cause 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, 

 may be increased during fever; following the crisis, however, the out- 

 put of this element may be decreased. It may also be increased in 

 conditions associated with acidosis. 



Calcium and Magnesium 



The greater part of the calcium and magnesium excreted in the 

 urine is in the form of phosphates. The daily output of calcium, which 

 depends principally upon the nature of the diet, aggregates on the 

 average about 0.1-0.4 gram (expressed as CaO) per day. The per- 

 centage of calcium salts present in the urine at any one time (10-40 

 per cent of total calcium output) forms no dependable index as to the 

 absorption of this class of salts, since they are again excreted into the 

 intestine after absorption. It is therefore impossible to draw any satis- 

 factory conclusions regarding the excretion of calcium unless we obtain 

 accurate analytical data from both the feces and the urine. 



