284 Gooch and Brooks — Rapid method for the 



appreciable volatilization of bromine or chlorine takes place 

 during the complete expulsion of the iodine by boiling. For 

 the quantitative separation of the iodine of 5 grm. of potassium 

 iodide from a solution containing 0*5 grm. of potassium bromide 

 and 0*5 grm. of potassium chloride it was found best to use 

 from 1 to 2 cm 3 of strong sulphuric acid, and to introduce into 

 the solution, measuring approximately 700 cm 3 in volume, 0'5 

 grm. of potassium nitrite, or its equivalent in nitrous fumes. It 

 is obvious that work upon this scale is undesirable in rapid 

 qualitative testing. For such purposes it is not a matter of 

 moment that a portion of the substances looked for escapes 

 the reaction, provided enough is left to furnish the indication 

 sought. We planned, therefore, to attempt the separation of 

 iodine from bromine and chlorine by applying the reaction 

 just mentioned to small amounts of liquid in test-tubes, in the 

 hope that the known losses of chlorine and bromine under the 

 conditions would be proportioned to the strength of the solu- 

 tion, or in other words, that when the amounts of bromine and 

 chlorine were very small they would escape volatilization, or 

 that when large a sufficiency would remain to give strong tests. 



The detection of the iodine is, of course, simple. We chose 

 for this purpose the reaction with sulphuric acid and potassium 

 nitrite. If the amount of iodine present is large it shows at once 

 in this test, and the same portion may be treated further to sepa- 

 rate the iodine, [f the amount of iodine is small it may be 

 found, as usual, by shaking the liquid with chloroform, or car- 

 bon disulphide or other appropriate solvent for iodine ; or, 

 in this case also, the portion under test may be utilized, if it is 

 desirable, for the separation of the iodine, and for the detection 

 of this element recourse may be had to the exposure of red 

 litmus paper to the fumes of the boiling solution according to 

 methods prescribed in the work referred to above upon the 

 quantitative separation of the iodine, — the paper taking on a 

 gray blue color when exposed to very minute traces of the 

 vapor of iodine, and a proportionately deeper color as the 

 amount of iodine increases. After the iodine is separated, bro- 

 mine and chlorine are easily found if present. We selected as 

 the most available method for detecting bromine the action of 

 sodium hypochlorite upon the acid solution and shaking with the 

 proper solvent. For the detection of chlorine we make use of 

 a modification of the well known chlorochromic anhydride test. 



As a preliminary step to the investigation of the reliability 

 of our method of separating iodine from bromine, tests were 

 made, for the purpose of securing definite points of compari- 

 son, upon the degree of delicacy of the hypochlorous acid test 

 for bromine. In these tests measured amounts of a solution of 

 potassium bromide were drawn from a burette into test-tubes. 



