Detection of Iodine, Bromine, and Chlorine. 287 



easily found in the residue remaining after the expulsion of 

 the iodine from 0*1 grm. of potassium iodide as in that left 

 after the expulsion of the iodine from O0070 grm. of the same 

 salt, and the indications in the experiments in which the ratio 

 of the iodine to the bromine remained the same while the ab- 

 solute amounts of both varied are precisely the same as those 

 of the experiments in which the maximum amount of iodine 

 remained unchanged throughout the variations in the amount 

 of bromide used. The maximum amount of potassium iodide 

 employed in these tests was 0"1 grm., but there is no reason to 

 suppose that this amount is not far below the maximum which 

 may be successfully handled in this process. 



For the detection of chlorine we modified the well-known 

 chlorochromic anhydride process so that the distillation may be 

 performed in an ordinary test-tube. The substance to be tested 

 is, if solid, placed in a large test-tube — 15 cm x2 cm is a good size 

 — and treated with sulphuric acid and potassium dichromate in 

 the manner to be described. The substance, if a liquid, is ren- 

 dered alkaline, if necessary, by sodium carbonate and evapo- 

 rated to dryness in the test-tube with care to remove all mois- 

 ture from the sides of the tube. This operation is effected 

 without trouble if the tube is inclined, as much as is possible 

 without spilling the liquid, and agitated continually while the 

 flame is applied to the higher parts The evaporation effected, 

 a little powdered potassium dichromate is introduced through 

 a funnel with care to prevent its touching the upper parts of 

 the tube, two or three cubic centimeters of strong sulphuric 

 acid are added, and a trap consisting of a straight two-bulbed 

 drying-tube cut off about an inch from the large bulb is hung 

 in the mouth of the test-tube, the precaution having been first 

 taken to moisten the interior of the bulbs with water without 

 wetting the wide, straight portion which hangs within the test- 

 tube. If a chloride is present the evolution of chlorochromic 

 anhydride begins as soon as this sulphuric acid touches the dry 

 salts in the bottom of the tube, and gentle heating, with a little 

 agitation, quickly completes the evolution of the chlorine com- 

 pound. It is the function of the moisture in the bulbs to de- 

 compose the fumes of the chlorochromic anhydride and to re- 

 tain the chromic acid thus produced. When more than a mere 

 trace of chlorine is present the yellow drops produced in the 

 moistened bulbs are, in the absence of a bromide, sufficiently 

 indicative of the presence of chlorine in the original substance, 

 but the delicacy of this test is much increased by washing out 

 the bulbs with a little distilled water and adding to the solu- 

 tion, as Wiley recommends,* a few drops of a solution of lead 

 acetate, which precipitates the yellow chromate or intensifies 

 the color of the solution according to the amount of chromic 



* Am. Chem. Jour., ii, 248. 



