CHLORIDES 77 



the standard silver nitrate solution, actually utilized in the precip- 

 itation, by 0.010. If it is desired to express the result in percent- 

 age of sodium chloride move the decimal point one place to the 

 right. 



In a similar manner the weight, or percentage of chlorine may 

 be computed using the factor 0.006 instead of 0.010. 



Calculate the quantity of sodium chloride and chlorine in the 

 twenty-four-hour urine specimen. 



CHLORIDES 



Volhard- Harvey Method 1 



Principle. This procedure differs from the Volhard-Arnold 

 method in that the excess of silver nitrate is titrated directly 

 without filtering and hence in the presence of the silver chloride. 

 The procedure is thus more rapid, but the exact end-point is more 

 difficult to determine. 



Procedure. Introduce 5 c.c. of urine into a small porcelain 

 evaporating dish or casserole and dilute with about 20 c.c. of 

 distilled water. Precipitate the chlorides by the addition of 10 c.c. 

 of standard silver nitrate solution and add 2 c.c. of acidified 

 indicator. Now run in a standard ammonium thiocyanate solution 

 from a burette until a faint red-brown tint is visible throughout 

 the mixture. This point may be determined readily by permitting 

 the precipitate to settle somewhat. Calculate the sodium chloride 

 value as indicated below. 



(If a red tint is produced when the first drop of thiocyanate is 

 added an additional 10 c.c. of the standard silver nitrate solution 

 must be introduced. The titration should then proceed as above 

 described and proper allowance made in the calculation for the 

 extra volume of silver nitrate employed.) 



Calculation. Since 2 c.c. of the ammonium thiocyanate solu- 

 tion is equivalent to 1 c.c. of the silver nitrate solution, divide the 

 burette reading by 2 and subtract the quotient from 10 c.c., the 

 quantity of silver nitrate solution taken. This value is the number 

 of cubic centimeters of silver nitrate solution actually used in the 

 precipitation of the chlorides. As 1 c.c. of the silver nitrate solu- 

 tion is equivalent to 0.01 gm. of sodium chloride, the number of 

 1 Harvey; Arch. Int, Med., 1910, 6, 12. 



