URINE ' 481 



by matching the colors produced when a few drops of indicator are added 

 respectively to the diluted urine and to standard solutions of known 

 reaction similarly diluted. Similar hydrogen ion concentrations 

 are indicated by similar colors. The indicator must be properly 

 chosen. 



Standard Solutions. A series of standard solutions of known hy- 

 drogen ion concentration must be prepared. The solutions as indi- 

 cated in Table I (page 482) are satisfactory for urine analysis. The 

 table also indicates the H ion concentration of each solution, the figure 

 given being the logarithm of this concentration (PH+)- It is more 

 convenient and rational to express the concentration by this logarithmic 

 notation. True H ion concentrations corresponding to the logarithmic 

 figures are given in Table II (page 482). 



The 13 solutions indicated are .made up by mixing equal volumes 

 of their ingredient solutions of the composition indicated. Solutions 

 4 to 12 are all that are ordinarily required as the normal urinary H 

 ion concentrations lie between 4.80 and 7.50 and pathological variations 

 are usually within these limits. The mean normal value is almost 

 exactly 6.00. 



Procedure. Select eleven 250 c.c. flasks of good glass and indistinguishable 

 in color and form. Into each of ten of these introduce 10 c.c. of the various stand- 

 ard solutions. Make up to 250 c.c. with distilled water and add to each exactly the 

 same amount of an aqueous solution of sodium alizarine sulphonate (10-15 drops). 

 Mix well by inverting. Introduce 10 c.c. of the urine to be tested into a similar 

 250 c.c. flask, dilute and add indicator in exactly the same way as before. Match 

 the color of the diluted urine solution with one of the standard solutions. By 

 consulting Table II (page 482) determine to what H ion concentration this corre- 

 sponds. This table points out the indicators to be used for different ranges of 

 acidity. From 5.3-6.7 />-nitrophenol is satisfactory and is used in the same way 

 as alizarin except that it must be present in concentration of 0.08 per cent. 

 Neutral red is used in the same way for acidities from 6.7-7.5 about 1.5 c.c. of 

 the i per cent solution being required. For acidities greater than 5.5 methyl red 

 is used in the following way : 10 c.c. portions of the standard solutions are intro- 

 duced into carefully selected colorless test-tubes and 10 c.c. of urine is introduced 

 into another tube. The standard solutions are then colored to match the urine 

 by the addition of small amounts of ^-nitrophenol, methyl orange, alizarine or 

 bismark brown. Then to standard solutions and urine add 0.15 c.c. of a satu- 

 rated solution in 50 per cent alcohol, of methyl red and match the colors. For 

 concentrations of 7.5-9.27 or less undiluted urine is matched in test-tubes against 

 undiluted standard solutions, using phenolphthalein as an indicator (without 

 previous coloration of standard solution). In all cases estimations are made in 

 duplicate. 



