PHYSIOLOGICAL CHEMISTRY 



409 



The amount of urine is increased by the imbibition of large quantities 

 of liquid and by certain drugs called diuretics; it is diminished by 

 excessive sweating or diarrhoea, and by failure of the heart's action. 



Specific Gravity. This is determined by a special form of hydro- 

 meter a urinometer graduated so that the zero mark 1000 cor- 

 responds to distilled water (Fig. 237). 



EXPERIMENT I. Fill a urine testing glass with urine cooled to 

 room temperature, place the urinometer in it, and 

 read off the graduation which is on a level with the 

 surface of the urine. Be careful that the urinometer 

 does not stick to the sides of the vessel. 



The average density varies between 1015 and 1025, 

 but a highly concentrated urine, e.g. after severe 

 sweating, may reach 1035, or a very dilute one, 

 e.g. after huge potations, 1002, and still be healthy. 

 A specific gravity over 1030, however, usually indi- 

 cates the presence of sugar or the existence of high 

 fever, and one much below 1010 should raise sus- 

 picions of renal trouble. 



Reaction. Healthy urine usually reacts acid to 

 litmus. This acidity is due to sodium dihydrogen 

 phosphate, NaH 2 P0 4 , not to free acid. 



EXPERIMENT II. Test the reaction of urine with 

 blue litmus paper and congo red paper. The litmus 

 is turned red, but the congo red is not altered, as it 

 is not affected by the acid salts of any but the 

 strongest acids (see Digestion, p. 376). 



The alkaline phosphate, Na 2 HP0 4 , may be present 

 in urine. It is detected by the addition of calcium 

 chloride to the urine, when a precipitate of calcium 

 phosphate forms if the alkaline phosphate is present, 

 but not if the acid phosphate alone is present The 

 amount of alkaline phosphate may be sufficient to 

 cause the urine to have an amphoteric reaction, turn- 

 ing red litmus blue and blue litmus red, or even to 

 have a definite alkaline reaction. This is often the 

 case during the stage of digestion, when hydrochloric 

 acid is being poured into the stomach, as the removal of hydrochloric 

 acid from the blood leaves an excess of bases. 



Besides the alkaline phosphate, alkaline bicarbonates may be present 

 in urine, causing an effervescence on the addition of acid. This is the 

 case when salts of oxidisable acids (e.g. citric, tartaric, etc.) are being 



FIG. 237. The urino- 

 meter. 



