480 PHYSIOLOGICAL CHEMISTRY 



25:y::y':x (acidity of 24-hour urine expressed in cubic centimeters of N/io 



sodium hydroxide). 



Each cubic centimeter of N/io sodium hydroxide contains 0.004 gram of 

 sodium hydroxide, and this is equivalent to 0.0063 gram of oxalic acid. There- 

 fore, in order to express the total acidity of the 24-hour urine specimen in equiva- 

 lent grams of sodium hydroxide, multiply the value of x, as just determined, 

 by 0.004, o f multiply the value of x by 0.0063 if it is desired to express the total 

 acidity in grams of oxalic acid. 



Interpretation. (Under the heading " Interpretation" there will 

 be found, in connection with the various quantitative methods which 

 follow, brief notes as to the possible significance of the results ob- 

 tained. For some further points (and reference to literature) see the 

 chapters on the Normal and Pathological Constituents of Urine and 

 on Metabolism. Consult text-books on physiological chemistry and 

 clinical diagnosis for complete discussion). The acidity of the urine 

 expressed in cubic centimeters N/io alkali required to neutralize the 

 24-hour output varies ordinarily from 200 to 500 under normal con- 

 ditions with an average of perhaps 350. It is dependent almost 

 entirely upon the diet, being low on a vegetable (base-forming diet) 

 and high on a diet containing much meat, rice, whole wheat products, 

 fruits containing benzoic acid, as prunes and cranberries, etc. (acid- 

 forming foods). On the administration of 15 grams of sodium bicar- 

 bonate it may go down to 100; the ingestion of much acid-forming 

 food may increase it to 600. In fasting it may rise in a few days to 

 800. It must be borne in mind that acidities of less than 250 usually 

 indicate a true alkalinity of the urine inasmuch as phenolphthalein 

 changes in an alkaline solution. Samples of urine collected shortly 

 after a meal may be alkaline due to the so-called " alkaline tide." 



Bacterial decomposition of the urea of the urine occurring in the 

 urinary tract will increase the amount of ammonia and decrease the 

 acidity of the urine. The same change usually occurs in urine left in 

 contact with the air. The acidity of the urine is increased in acidosis, 

 cardio-renal and certain other disorders. The acidity of the urine 

 may be somewhat increased by administration of mineral acids, acid 

 phosphates, or benzoates, but it is much more difficult to increase than 

 to decrease this acidity. 



Hydrogen Ion Concentration or True Acidity 



Indicator Method (Henderson and Palmer's Adaptation of Soren- 

 sen's Method). 1 Principle. The reaction of the urine is estimated 



1 Henderson and Palmer: Jour. Biol. Chem., 13, 393, 1913. 



