462 



PHYSIOLOGICAL CHEMISTRY. 



gently) the reaction is due to the fixed alkalies; if the red color reap- 

 pears, the alkaline effect is due to ammonia compounds. 



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 

 FIG. 42. monosodium orthophosphate, NaH 2 P0 4 , which 



has an acid, and of disodium orthophosphate, 

 ^, which has an alkaline reaction. 



Experiment 71. Prepare normal soda solu- 

 tion as directed on page 258, dilute it with 9 

 parts of water, and titrate with this deci- nor- 

 mal solution 100 c.c. of urine, using litmus- 

 paper as an indicator. 



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 in- 

 dicate the presence of sugar, larger 

 quantities of which may cause the spe- 

 cific gravity to rise to 1.050. Albu- 

 minous urine is frequently of low 

 specific gravity, 1.010 to 1.012. 



It should be remembered that the 

 specific gravity of urine considered sep- 

 arately 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 



accomplished by the urinometer, which is a small hydrometer indicat- 



ing specific gravity from zero (or 1000) to 60 (or 1060). (See Fig. 



42.) As the temperature influences the density of liquids, a urin- 



ometer can only give correct results at a certain degree of temperature, 



which is generally marked upon the instrument. 



Urinometer. 



