URINE 



503 



Group i. To 50 c.c. of M/5 KC1 add the indicated number of c.c. 

 of M/5 HC1 and dilute to 200 c.c. Indicator: thymol blue. 



Group 2. To 50 c.c. of 0.2 M acid potassium phthalate add the 

 indicated number of c.c. of 0.2 N HC1 and dilute to 200 c.c. Indica- 

 tors: thymol blue and brom-phenol blue. 



Group 3. To 50 c.c. of 0.2 M acid potassium phthalate add the 

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

 cators: brom-phenol blue, methyl red, and brom-cresol purple. 



Group 4. To 50 c.c. of 0.2 M acid potassium phosphate add the 

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

 cators: brom-cresol purple, brom- thymol blue, and phenol red. 



into a paraffined bottle, to which a burette and soda-lime guard tubes have been attached. 

 The solution is then accurately standardized against weighed amounts of the pure acid 

 potassium phthalate. To do this accurately weigh up about 1.6 gms. of the salt, dissolve 

 in about 30 c.c. of distilled water, add phenolphthalein and titrate with the alkali till a 

 faint but distinct and permanent pink is developed. A current of CO 2 free air should be 

 blown through the solution during the titration. 



Grams of phthalate used X 1000 ... ,., . XT ^^ 

 -r = Normality of NaOH. 

 204.14 X c.c. NaOH required 



It is not necessary to make exactly 0.2 N, but the true strength must be considered in 

 making standards. 



0.2 N Hydrochloric Acid. Dilute concentrated HC1 to 20 per cent. Distill, dilute 

 distillate, and standardize against the standard soda, using methyl red as the indicator. 



