Gooch and Brooks — Rapid method for Detection, etc. 283 



The molecular rotation of the several tartrates which come 

 into consideration here are, (from Landolt's results and my 

 own) : 



K„C 4 H 4 6 = 64°-42 KNaC 4 H 4 6 = 62°-34 



(NH 4 );C 4 H 4 0. = 63°-04 KNH 4 C 4 H 4 6 = 63°24 



Na„"C 4 HO = 59°-85 NaNHC 1 HO B = 6l°'7l 



2 4 4 6 4440 



On the general hypothesis of replacement in the tartrate mole- 

 cule by excess of inactive salts these numbers show why the 

 addition of JSTH 4 C1 should produce but a slight change, while 

 that of NaCl must produce a much greater one in the rotation 



of ;n t h 4 kc 4 h 4 o 6 . 



These results, like those obtained with the antimony com- 

 pound, suggest the value of the polariscope method in the 

 study of problems of chemical affinity. This method has been 

 applied in a limited number of cases but the experiments 

 above detailed indicate a direction in which it may be devel- 

 oped. That a certain interval of time is necessary to complete 

 these reactions, even where no precipitates are formed, is 

 shown by experiments 9, 10 and 11. The polariscope affords 

 us a ready method, possibly the only method, of following 

 these changes, which are of sufficient importance to merit 

 further study. 



Chicago, July 10th, 1890. 



Art. XXXVII. — A Rapid method for the Detection of 

 Iodine, Bromine, and Chlorine in presence of one 

 another ; by F. A. Gooch and F. T. Brooks. 



[Contributions from the Kent Chemical Laboratory of Tale College — V.] 



The conditions under which iodine may be set free and sepa- 

 rated quantitatively from hydrochloric and hydrobromic acid by 

 the action of nitrous acid upon the acidulated solutions of the 

 haloid salts have been recently studied in this laboratory.* 

 We have endeavored in the work which is here described to so 

 modify the quantitative process that the same principles of 

 action may be applied rapidly and easily to the qualitative de- 

 tection of iodine, bromine, and chlorine, without decreasing to 

 too great a degree the delicacy of the indications. It was 

 found in the work referred to that when sulphuric acid is 

 added to the aqueous solution of a soluble chloride, bromide, 

 and iodide, with care to keep the proportion of acid within 

 certain limits and the dilution of the liquid sufficient, no very 



* This Journal, xxxix, 293, and xl, 145. 



