30 METHODS FOR THE ANALYSIS OF URINE 



wash the apparatus and test again. Rinse out the traces of indi- 

 cator solution with distilled water and proceed with the estimation. 



First make the preliminary determination as follows: To 20 

 c.c. of distilled water in a 2-ounce square bottle add 1 c.c. of rosolic 

 acid solution and immediately add the urine 0.2 c.c. at a time 

 comparing with the rosolic acid permanent standards after each 

 addition until either the P H determination remains constant or the 

 urinary pigment changes the character of the color. Never 

 use more than 1 c.c. of urine. In the case of highly concentrated 

 urine 0.2 or 0.4 c.c. will suffice. This test indicates the amount 

 to use in the final test, i.e., less than will give the disturbing pig- 

 ment effect but still enough to give the full P H estimation. 



The test also shows which indicator must be used. If the 

 mixture is as yellow as the 5.9 rosolic standard or more yellowish, 

 use methyl red. If it is as red as the 7 rosolic standard or of a 

 deeper red color, use neutral red. If the color is intermediate 

 between that of the 5.9 and 7 standards, use rosolic acid. 



For the final test add to 20 c.c. of distilled water the amount of 

 urine determined by the first test, and last of all 1 c.c. of the proper 

 indicator. Compare with the standards immediately (because 

 contamination with carbon dioxide occurs so easily, and in the case 

 of rosolic acid the color fades rapidly). Avoid getting expired air 

 into the bottle. 



It is self-evident that one must be careful to compare the urine 

 mixture only with those standards that correspond to the particu- 

 lar indicator used (for instance, after using rosolic acid for the urine 

 do not match up with the colors given by methyl red or neutral 

 red) . It is advisable to have each standard bottle labeled with the 

 indicator, for example, Methyl R. 5.3, Ros. 6.8, Neutral R. 7.4; 

 thus accidental slips will be avoided. 



The PH figure of the permanent standard that most nearly 

 matches in color the urine test solution is taken as the PH of 

 the urine. One may guess PH readings intermediate between the 

 standards although such interpolation is an unnecessary refine- 

 ment. The most accurate and most rapid estimations are made 

 by placing the standard bottle and the urine bottle for compari- 

 son against a background of dull white paper with the light 

 (diffused daylight or electric light) passing over the shoulder. 



Remarks. 1. Toluene is to be added to the urine as a preserva- 

 tive when collecting a 24-hour sample, or when the urine cannot 



