54 



PHYSIOLOGICAL CHEMISTRY 



Group 5. To 50 c.c. of 0.2 M boric acid in 0.2 M KC1 add the 

 indicated number of c.c. of 0.2 N NaOH and dilute to 200 c.c. Indi- 

 cators: cresol red and thymol blue. 



Total Solids 



1. Drying Method. Place 5 c.c. of urine in a weighed shallow dish, acidify 

 very slightly with acetic acid (1-3 drops), and dry it in vacuo in the presence of sul- 

 phuric acid to constant weight. Calculate the percentage of solids in the urine 

 sample and the total solids for the 24-hour period. 



Interpretation. The average excretion of total solids by a normal adult man is 

 about 70 grams. It is largely dependent upon the protein and salts of the diet. 

 It may be decreased in severe nephritis due to impaired excretion, and greatly in- 

 creased in diabetes with high sugar elimination. 



Practically all the methods the technic of which includes evaporation at an 

 increased temperature, either under atmospheric conditions or in vacuo, are attended 

 with error. 



Shackell's method 1 which entails the vacuum desiccation of the frozen sample 

 is extremely satisfactory and should be used in all biological work where the great- 

 est accuracy is desired. 



2. Calculation by Long's Coefficient. The quantity of solid material contained 

 in the urine excreted for any 24-hour period may be approximately computed by 

 multiplying the second and third decimal figures of the specific gravity by 2.6. 

 This gives us the number of grams of solid matter in i liter of urine. From this value 

 the total solids for the 24-hour period may easily be determined. 



Calculation. If the volume of urine for the 24 hours was 1120 c.c. and the spe- 

 cific gravity 1.018, the calculation would be as follows: 



(a) 18 X 2.6 = 46.8 grams of solid matter in i liter of urine. 



(b) 



46.8 X 1120 



1000 



= 52.4 grams of solid matter in 1120 c.c. of urine. 



Long's coefficient was determined for urine whose specific gravity was taken 

 at 25C. and is probably more accurate, for conditions obtaining in America, than 

 the older coefficient of Haeser, 2.33. 



Interpretation. See above. 



Total Nitrogen 



i. Kjeldahl Method. 2 Principle. The principle of this method is 

 the conversion of the various nitrogenous bodies of the urine into am- 



1 Shackell: American Journal of Physiology, 24, 325, 1909. 



2 There are numerous modifications of the original Kjeldahl method; the one described 

 here, however, has given excellent satisfaction and is recommended for the determination of 

 the nitrogen content of urine. 



