Detection of Iodine, Bromine, and Chlorine. 289 



The distinctness of the color obtained in this process seems 

 to be diminished a little by the process of liberating the iodine, 

 but the lowest reach of the test is not very materially different 

 from that made upon the pure chloride. In the following sim- 

 ilar tests made with mixtures containing beside the chloride 

 potassium bromide alone, or the bromide as well as iodide, the 

 phenomena observed were the same, excepting that the fumes 

 of the bromine evolved when much bromide is present rise 

 with the chlorochromic anhydride and, dissolving in the film 

 of moisture in the trap, give to it their own characteristic color, 

 and so obscure the effect of chromic acid. In these experi- 

 ments, therefore, the washings of the bulbs were first rendered 

 faintly ammoniacal and gently heated to destroy the free bro- 

 mine, and then the solution was acidified with acetic acid and 

 tested as described with lead acetate and ammonium acetate. 



KI taken. 



KBr taken. 



KC1 tal 



en. 



Final volume. 



Reaction obtained. 



— 



O'l grm. 



0-0030 



grm. 



5 



cm. 3 



Marked precipitation. 



— 



o-i 



0-0020 





5 





Distinct precipitation. 



— 



01 



o-ooio 





5 





Distinct color. 



— 



o-i 



0-0005 





5 





Faint color. 



— 



01 



0-0005 





5 





Faint color. 



— 



o-i 



0-0004 





5 





Faintest color. 



— 



o-i 



0-0003 





5 





Doubtful color. 



— 



o-i 



0-0002 





5 





Doubtful color. 



— 



o-i 



o-oooi 





5 





None. 



- l grm. 



o-i 



0-0010 





5 





Distinct color. 



0-1 



o-i 



0-0010 





5 





Distinct color. 



o-i 



o-i 



o-ooio 





5 





Distinct color. 



, The evolution of considerable amounts of bromine appears, 

 therefore, to diminish the delicacy of the test in some degree, 

 but 0'0005 grm. of chlorine — the amount in 0'0010 grm. of po- 

 tassium chloride — is indicated unmistakably in the presence of 

 0*1 grm. of potassium bromide, and 0*1 grm. of potassium 

 iodide, and the test may probably be relied upon to show half 

 that amount of chlorine. The potassium iodide, as already 

 mentioned, was specially prepared for the work, and contained 

 in the amounts which we used no recognizable trace of chlorine. 

 The potassium bromide contained of chlorides enough to show 

 an indication in 0*5 grm. of the salt. We were unable to find 

 the chlorine in 02 grm. of the salt, and so considered it safe 

 to employ half this latter amount in our experiments as being 

 sufficiently free from chlorine for the purpose. 



The process which we propose for the rapid qualitative de- 

 tection of the halogens in presence of one another may be sum- 

 marized briefly, as follows : 



To detect iodine, the solution of the substance under exami- 

 nation is acidulated with dilute sulphuric acid and treated with 

 a drop or two of a solution of sodium or potassium nitrite free 



