760 URINE. 



The silver-nitrate solution may be a N/10 one. It is often made of 

 such a strength that each cubic centimeter corresponds to 0.006 gram 

 Cl or 0.01 gram NaCl. This last-mentioned solution contains 29.075 

 grams of AgNOs in 1 liter. 



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

 tions of MOHR'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 AgN0 3 solution and correct the sul- 

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

 responds 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 

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



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

 Chem., 20. 



