290 Gooch and Brooks — Rapid method for Detection, etc. 



from chlorine. Unless the amount present is small, the iodine 

 shows itself in the color of the solution and in the vapors which 

 escape. Small amounts may be found by shaking the liquid 

 with carbon disulphide in the usual manner, or, when economy 

 of material is desirable, by gently heating the prepared solu- 

 tion and testing the escaping fumes with red litmus paper, 

 thus utilizing the same portion of material for the detection of 

 the iodine and for its separation preparatory to testing for 

 bromine and chlorine. 



To remove the iodine previous to making the tests for bro- 

 mine and chlorine, a few drops of dilute sulphuric acid and a 

 like amount of a dilute solution of sodium or potassium nitrite 

 (prepared free from chlorine as described) are added to the solu- 

 tion of the substance in a test-tube, and the liquid is boiled 

 with constant agitation. When the color of iodine disappears 

 from the fumes and the solution, a drop or two more of sul- 

 phuric acid, and of the nitrite, are again added, and the boiling 

 is repeated. When the escaping steam no longer gives to red 

 litmus paper the characteristic gray blue color due to the 

 action of iodine, the process of separation is complete. 



A portion of the solution thus prepared is tested for bromine 

 by cautiously adding a dilute solution of sodium hypochlorite 

 and shaking with colorless carbon disulphide. 



The test for chlorine is made in a second portion of the solu- 

 tion from which the iodine has been removed. The liquid is 

 neutralized with sodium carbonate or hydrate free from chlo- 

 rine, evaporated to dryness in a test-tube and treated as de- 

 scribed with sulphuric acid and potassium dichromate, the 

 fumes of the chlorochromic anhydride which arise on gentle 

 warming being condensed and converted to chromic acid by 

 the film of moisture upon the interior walls of the trap. 

 The trap is washed out with a very little distilled water (5 cm. 3 

 are enough), and the washings made slightly ammoniacal to de- 

 stroy free bromine, if necessary, and after gentle warming 

 again acidified, are tested with lead acetate. If the yellow 

 chromate is precipitated the presence of chlorine in the origi- 

 nal substance is proved. If the precipitate is white, as is very 

 likely to be the case, a few drops of a saturated solution of 

 ammonium acetate are added with caution, and the whole is 

 gently warmed to dissolve the white sulphate. On cooling the 

 solution and shaking (or immediately if much chromic acid has 

 been formed), the yellow chromate falls, or gives color to the 

 solution according as the chloride was originally present in 

 large or small amount. 



The process is rapid and sufficiently exact for qualitative 

 testing in general. 



