396 PHYSIOLOGICAL CHEMISTRY. 



25 c.c.) of distilled water acidified with about 10 drops of nitric 

 acid. Transfer the solution to a small beaker, being sure to 'rinse 

 out the crucible or dish very carefully. Test the reaction of the 

 fluid, and if not already acid in reaction to litmus, render it slightly 

 acid with nitric acid. Now neutralize the solution by the addition 

 of calcium carbonate in substance, 1 add 2-5 drops of neutral potas- 

 sium chromate solution to the mixture and titrate with a standard 

 argentic nitrate solution. 2 



This standard solution should be run in from a burette, stirring 

 the liquid in the beaker after each addition. The end-reaction is 

 reached when the yellow color of the solution changes to a slight 

 orange-red. At this point take the burette reading and compute 

 the percentage of chlorine and sodium chloride in the urine ex- 

 amined. 



Calculation. Since I c.c. of the standard argentic nitrate solu- 

 tion is equivalent to o.oio gram of sodium chloride, to obtain the 

 weight, in grams, of the sodium chloride in the 10 c.c. of urine 

 used multiply the number of cubic centimeters of standard solu- 

 tion used by o.oio. If it is desired to express the result in per- 

 centage of sodium chloride move the decimal point one place to 

 the right. 



To obtain the zveight f in grams, of the chlorine in the 10 c.c. of 

 urine used multiply the number of cubic centimeters of standard 

 solution used by 0.006, and if it is desired to express the result 

 in percentage of chlorine move the decimal point one place to the 

 right. 



Calculate the quantity of sodium chloride and chlorine in the 

 twenty-four hour urine specimen. 



3. Volhard-Arnold Method. Place 10 c.c. of urine in a 100 

 c.c. volumetric flask, add 2030 drops of nitric acid (sp. gr. .1.2) 

 and 2 c.c. of a cold saturated solution of ferric alum. If necessary, 

 at this point a few drops of an 8 per cent solution of potassium 

 permanganate may be added to dissipate the red color. Now slow- 

 ly run in the standard argentic nitrate 3 solution (20 c.c. is ordi- 

 narily used) until all the chlorine has been precipitated and an excess 



1 The cessation of effervescence and the presence of some undecomposed cal- 

 cium carbonate at the bottom of the vessel are the indications of neutralization. 



~ Standard argentic nitrate solution may be prepared by dissolving 29.060 grams 

 of argentic nitrate in I liter of distilled water. Each cubic centimeter of this 

 solution is equivalent to o.oio gram of sodium chloride or to 0.006 gram of 

 chlorine. 



3 See note (2) at the bottom of page 384. 



