RASKINS' MODIFICATION 27 



urine solution with one of the standard solutions. By con- 

 sulting Table II determine to what H ion concentration this cor- 

 responds. This table points out the indicators to be used for 

 different ranges of acidity. From 5.3 to 6.7 p-nitrophenol is satis- 

 factory and is used in the same way as alizarine 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 to 7.5 about 1.5 c.c. of 

 the 1 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 introduced 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 p-nitrophenol, methyl orange, 

 alizarine or Bismarck brown. Then to standard solutions and 

 urine add 0.15 c.c. of a saturated solution in 50 per cent alcohol, of 

 methyl red and match the colors. For concentrations of 7.5 to 

 9.27 or less undiluted urine is matched in test-tubes against undi- 

 luted standard solutions, using phenolphthalein as an indicator 

 (without previous coloration of standard solution). In all cases 

 estimations are made in duplicate 



RASKINS' MODIFICATION OF HENDERSON AND 

 PALMER'S METHOD l 



Principle. The principle involved is the same as that of Hen- 

 derson and Palmer except that permanent standards are sub- 

 stituted for the solutions in the latter. 



Permanent Standards. The artificial standards advocated 

 by Haskins are made by adding amaranth and paranitrophenol in 

 various proportions in a buffer mixture which contains KH2?O4 

 and K2HPO4, each being in one-tenth molar concentration. The 

 buffer solution (P H 6.8) prevents the trace of alkali which gradually 

 dissolves out of the glass of the bottles from changing the color of 

 the standards. This solution gives a decided yellow color when 

 paranitrophenol is added, the intensity of the color depending 

 upon the amount of paranitrophenol used. Amaranth imparts a 

 brilliant red color, and is not affected by the phosphate. 



The amaranth and paranitrophenol solutions should be kept 



Raskins: Jour. Lab. and Clin. Med., 1919, 4, 363. 



