URINE AND ITS CONSTITUENTS. 



707 



FIG. 73. 



Urine sometimes is amphoteric in its reaction, i. e., it colors red litmus-paper 

 faintly blue, and blue litmus-paper slightly red. This condition is caused most 

 likely by the simultaneous presence of monosodium orthophosphate, NaH 2 PO 4 , 

 which has an acid, and of disodium orthophosphate, NaH 2 PO 4 , which has an 

 alkaline, reaction. 



The acidity of the urine is best determined in the following manner 

 (Folin) : 25 c.c. of urine are shaken in a flask with 15 to 20 grammes 

 of powdered potassium oxalate, 1 to 2 

 drops of phenolphthalein (J per cent, 

 solution in alcohol) are added, and the 

 mixture titrated at once with $ sodium 

 hydroxide. The end-reaction is the for- 

 mation of a distinct pink color. The 

 acidity of the urine is usually expressed 

 in terms of -^ acid or alkali for twenty- 

 four hours. 



The oxalate is added to precipitate 

 calcium, and thus avoid the deposition 

 of calcium phosphate as the mixture 

 becomes alkaline. It also reduces the 

 error due to ammonium. 



Specific gravity. The normal spe- 

 cific gravity of an average amount of 

 1500 c.c. of urine passed in twenty-four 

 hours is about 1.020, but it varies, even 

 in health, from 1.012 to 1.030 or more. 

 A specific gravity above 1.030 may 

 indicate the presence of sugar, larger 

 quantities of which may cause the spe- 

 cific gravity to rise to 1.050. Albumi- 

 nous urine is frequently of low specific 

 gravity, 1.010 to 1.012, especially in 

 chronic nephritis. 



It should be remembered that the 

 specific gravity of urine considered 

 separately from the quantity of urine passed in twenty-four hours is 

 of no value, and that in some diseases (for instance in acute nephritis 

 with albuminuria) the specific gravity of albuminous urine may be as 

 high as 1.030, while a diabetic urine may have a specific gravity of 

 1.025, or less, in consequence of a large volume passed. 



The determination of the specific gravity of urine is generally accom- 



Urinometer. 



