CHLORINE DETERMINATION. 721 



FREUND and TOEPFER, as well as BODTKER/ have suggested modifica- 

 tions of MOHK'S method. 



VOLHARD'S METHOD. Instead of the preceding determination, VOL- 

 HARD'S method, which can be performed directly on the urine, may be 

 employed. The principle is as follows: All the chlorine from the urine 

 acidified with nitric acid is precipitated by an excess of silver nitrate, 

 filtered, and in a measured part of the filtrate the quantity of silver added 

 in excess is determined by means of a sulphocyanide solution. This 

 excess of silver is completely precipitated by the sulphocyanide, and a 

 solution of some ferric salt, which, as is well known, gives a blood-red 

 reaction with the smallest quantity of sulphocyanide, is used as an indicator. 



We require the following solutions for this titration: 1. A silver- 

 nitrate solution which contains 29.075 grams of AgNOs per liter and of 

 which each cubic centimeter corresponds to 0.01 gram NaCl or 0.00607 

 gram Cl. 2. A saturated solution at the ordinary temperature of chlorine- 

 free iron alum or ferric sulphate. 3. Chlorine-free nitric acid of a specific 

 gravity of 1.2. 4. A potassium-sulphocyanide solution which contains 

 8.3 grams KCNS per liter, and of which 2 cc. corresponds to 1 cc. of the 

 silver-nitrate solution. 



About 9 grams of potassium sulphocyanide are dissolved in water and diluted 

 to 1 liter. The quantity of KCNS contained in this solution is determined by the 

 silver-nitrate solution in the following way: Measure exactly 10 cc. of the silver 

 solution and treat it with 5 cc. of nitric acid and 1-2 cc. of the ferric-salt solu- 

 tion and dilute with water to about 100 cc. Now the sulphocyanide solution 

 is added from a burette, constantly stirring until a permanent faint-red colora- 

 tion of the liquid takes place. The quantity of sulphocyanide found in the solu- 

 tion by this means indicates how much it must be diluted to be of the proper 

 strength. Titrate once more with 10 cc. of AgNO 3 solution and correct the sul- 

 phocyanide solution by the careful addition of water until 20 cc. exactly corre- 

 sponds to 10 cc. of the silver solution. 



The determination of the chlorine in the urine is performed by this 

 method in the following way: Exactly 10 cc. of the urine are placed in a 

 flask which has a mark corresponding to 100 cc. and which is provided 

 with a stopper; 5 cc. of nitric acid are added; dilute with about 50 cc. 

 of water and then allow exactly 20 cc. of the silver-nitrate solution to 

 flow in. Close the flask with the stopper and shake well, remove the stop- 

 per and wash it with distilled water into the flask, and fill the flask to the 

 100-cc. mark with distilled water. Close again with the stopper, care- 

 fully mix by shaking, and filter through a dry filter. Measure off 50 

 cc. of the filtrate by means of a dry pipette, add 3 cc. of ferric-salt solu- 

 tion, and allow the sulphocyanide solution to flow in until the liquid 

 above the precipitate has a permanent red color. The calculation is 

 ver\ simple. For example, if 4.6. cc. of the sulphocyanide solution 

 was necessary to produce the final reaction, then for 100 cc. of the filtrate 

 (=10 cc. urine) 9.2 cc. of this solution are necessary. 9.2 cc. of the 

 sulphocyanide solution corresponds to 4.6 cc. of the silver solution, 

 and since 20 4.6=15.4 cc-. of the silver solution was necessary to com- 

 pletely precipitate the chlorine in 10 cc. of the urine, then 10 cc. con- 



1 Freund and Toepfer, see Maly's Jahresber., 22; Bodtker, Zeitschr. f. physio! . 

 Chem., 20. 



