30 THE ANALYSIS OF POTASSIC BROMIDE. 



num. Slightly more than the equivalent quantity of acid was added, and 

 the oxalate obtained was therefore slightly acid. As will be shown, the 

 acidity was later the cause of much inconvenience, and had better have 

 been avoided. The oxalate was four times systematically recrystallized in 

 platinum with centrifugal draining each time. The final product, like the 

 previous one, gave no tests for impurities except a slight excess of acid; 

 it was used as the source of potassium for one preparation of potassium 

 bromide. 



BROMINE. 



Although the methods previously used at Harvard had afforded a 

 satisfactory yield of very pure bromine, 1 it was desired to add to the 

 knowledge on the subject by testing another method. Through the gener- 

 osity of the Mallinckrodt Chemical Works of St. Louis, Missouri, and 

 also of the Dow Chemical Works of Midland, Michigan, a large quantity 

 of potassic bromate was placed at our disposal. Repeated crystallization, 

 very kindly carried out for us on a large scale by these firms, had been 

 the method used in its purification. 



This material, which served as our starting-point, was already very 

 pure, a fact which was indicated by three syntheses of argentic bromide 

 from purest silver and potassic bromide obtained by decomposing the 

 Mallinckrodt bromate. These syntheses, carried out with all necessary 

 precautions, gave, respectively, 57.441, 57.440, 57.441 as the percentage of 

 silver in argentic bromide. According to Baxter the true amount is 

 57. 445. 2 The slight difference indicates a trace of iodine rather than 

 chlorine ; but this impurity can be easily expelled, while chlorine is far 

 more troublesome. 



It having been demonstrated that recrystallization is an effective means 

 of purifying the salt from chlorate and chloride, a large quantity of 

 potassic bromate was three times recrystallized in porcelain, the crystals 

 being centrifugally whirled each time and all mother liquors discarded. 

 This gave an exceedingly pure bromate, much purer than Stas could have 

 obtained, 3 because the centrifugal draining makes so great a difference 

 in the rate of purification.* 



A large quantity of the salt was decomposed into the bromide in a 

 platinum dish by the heat of an alcohol lamp. The potassic bromate in 

 decomposing attacked the platinum, and the mass of bromide was slightly 



1 See Proc. Am. Phil. Soc., 43, 119 (1904), for references and Stas, Mem. Acad. 

 P.elgique, 43, II, 38 (1882). 



2 Baxter, Journ. Am. Chcm. Soc., 28, 1332 (1906). See also Richards, Trans. 

 Am. Phil. Soc., 43, 119 (1904). 



3 Untersuchungen, 160. 



4 Richards, Journ. Am. Chem. Soc., 27, 104 (1905). 



