364 



PHYSIOLOGICAL CHEMISTRY 



mining the specific gravity is by means of a urinometer (Fig. 1 16) . This 

 affords a very rapid method and at the same time is sufficiently accurate 

 for clinical purposes. The urinometer is always calibrated for use at a 

 specific temperature and the observations made at any other tem- 

 perature must be subjected to a certain correction to obtain the true 

 specific gravity. In making this correction one unit of the last order is 

 added to the observed specific gravity for every three degress above 

 the normal temperature and subtracted for every three 

 degrees below the normal temperature. For instance, 

 if in using a urinometer calibrated for i5C. the specific 

 gravity of a urine having a temperature of 2iC. is 

 determined as 1.018 it is necessary to add to the 

 observed specific gravity two units of the third order 

 to obtain the real specific gravity of the urine. There- 

 fore the true specific gravity, at i5C., of a urine 

 having a specific gravity of 1.018 at 2iC. is 1.018 -f- 

 0.002 = i. 020. 



Pathologically, the specific gravity may be sub- 

 jected to very wide variations. This is especially 

 true in diseases of the kidneys. In acute nephritis 

 ordinarily the urine is concentrated and of a high 

 specific gravity, whereas in chronic nephritis the re- 

 verse conditions are more apt to prevail. In fact, 

 under most conditions, whether physiological or patho- 

 logical, the specific gravity of the urine is inversely 

 proportional to the volume excreted. This is not 

 true of diabetes mellitus, however, where the volume 

 of urine is large and the specific gravity is also high, 

 owing to the sugar contained in the urine. 



The amount of solids eliminated in the excretion 

 OMETER AND CvLiN- for twenty-four hours may be roughly calculated by 

 means of Long's coefficient, i.e., 2.6. The solid con- 

 tent of 1000 c.c. of urine is obtained by multiplying the last two 

 figures of the specific gravity observed at 25C. by 2.6. To determine 

 the amount of solids excreted in twenty-four hours if the volume was 

 1 1 20 c.c. and the specific gravity was 1.018 the calculation would be as 

 follows : 



(a) 18X2.6 = 46.8 grams of solid matter in 1000 c.c. of urine. 

 ,..46.8X1120 

 (b) jooo^ = 5 2 -4 grams of solid matter in 1120 c.c. of urine. 



The coefficient of Haser (2.33) which has been in use for years prob- 

 ably gives values that are inaccurate for conditions existing in America. 



mti. 



FIG. 1 1 6. URIN- 



