394 PHYSIOLOGICAL CHEMISTRY. 



paper into a dry Erlenmeyer flask. Distil off the chloroform, heat 

 the residue on a boiling water-bath for 5 minutes in the open flask, 

 and wash the dried residue with hot water. 1 Add 10 c.c. of con- 

 centrated sulphuric acid to the washed residue, heat on the water- 

 bath for 5-10 minutes, dilute with 100 c.c. of water and titrate the 

 blue solution with a very dilute solution of potassium permangan- 

 ate. 2 The end-point is indicated by the dissipation of all the blue 

 color from the solution and the formation of a pale yellow color. 



Calculation. Ellinger claims that one-sixth of the amount deter- 

 mined must be added to the value obtained by titration in order 

 to secure accurate data. This correction should always be made. 



XIII. Chlorides. 



i. Clark's Modification of Dehn's Method. 3 In this method 

 the organic compounds, that hold the chlorine too firmly for its 

 quantitative precipitation with argentic nitrate, are destroyed by 

 oxidation with sodium peroxide. Sodium peroxide in the pres- 

 ence of water gives off nascent oxygen according to the following 

 equation. 



Na 2 O 2 + H 2 O = 2NaOH -f O 



The oxygen then attacks the organic matter and the chlorine is 

 left as sodium chloride. The procedure is as follows : To 10 c.c. 

 of urine in a 75-100 c.c. casserole, add 1.0-1.2 gram of sodium 

 peroxide and evaporate the mixture to dryness on a boiling water- 

 bath. In case the residue is not pure white, thus indicating that in- 

 sufficient sodium peroxide has been added, the residue should be 

 moistened with distilled water, additional sodium peroxide added, 

 and the mixture again evaporated to dryness. When the oxidation 

 is complete, treat the mass with 10-20 c.c. of distilled water and stir 

 until it has practically all been brought into solution. Then intro- 

 duce a bit of litmus paper and add dilute nitric acid ( i : i ) until the 

 litmus paper turns red and all effervescence ceases. Now place the 



1 The washing should be continued until the wash water is no longer colored. 

 Ordinarily two or three washings are sufficient. If a separation of indigo 

 particles takes place during the washing process, the wash water should be 

 filtered, the indigo extracted with chloroform and the usual method applied 

 from this point. 



2 A " stock solution " of potassium permanganate containing three grams per 

 liter should be prepared, and when needed for titration purposes a suitable 

 volume of this solution should be diluted with 40 volumes of water. The 

 potassium permanganate solution should be standardized with pure indigo. 



3 Private communication to the author from Mr. S. C. Clark. 



