Found. 





Calculated for 



B 



C 



K 3 Pb. 2 Br ? .4H 2 < 



10-41 



10-24 



9-43 



31-90 



32-49 



33-30 



52-15 



52-05 



51-48 



5-59 



5-28 



5-79 



100-05 



100-06 



100-00 



H. L. Wells — Halides of Potassium and Lead. 193 



prepared and it crystallizes well, but it is extremely unstable. 

 When exposed to the air it begins to whiten almost instantly, 

 giving off bromine. It is stable, however, in air containing a 

 considerable amount of bromine vapor, so that it can be dried 

 by pressing on paper in such an atmosphere. It is sufficiently 

 stable, when corked up in a weighing-tube, to be rapidly 

 weighed in a cold room without serious decomposition. 



Three crops of the double bromide were analyzed. A and 

 B were made, in each case, by adding 20 cc of bromine to 400 cc 

 of a cold solution which was saturated with potassium bromide 

 and lead bromide and allowing the mixture to stand over night. 

 C was made like the other crops, except that 30 cc of bromine 

 were used. 



A 



Potassium 10 33 



Lead 32-05 



Bromine. 51-96 



Water 



The analyses agree with the formula as well as could be ex- 

 pected, considering the instability of the compound. The 

 analyses show almost exactly one atom of extra bromine for 

 two atoms of lead, so that the compound is closely related to 

 the iodide if not exactly analogous to it. 



The satisfactory crystals of the bromide and the stability of 

 the iodide suggested the possibility that, if the two compounds 

 were really analogous as suspected, isomorphous mixtures of 

 the two could be made which would retain the desirable quali- 

 ties of both, so as to be solidly crystallized and stable enough 

 to be accurately analyzed. Experiments showed that isomor- 

 phous mixtures could be readily obtained which crystallized 

 satisfactorily, and it was found that even small amounts of 

 iodine had the effect of greatly increasing the stability of the 

 compound. It was noticed that when a product was made from 

 a solution containing free bromine and iodine in nearly atomic 

 proportions (BrI), an almost perfectly stable, bright red salt 

 was obtained. The color of this salt is far from being inter- 

 mediate between that of the black iodide and the dark brown 

 bromide, but, since the analyzed products contain about 23 

 atoms of bromine to one of iodine, it does not seem probable 

 that any definite relation between the two halogens exists. It 

 is remarkable that such a small proportion of iodine should 

 have so great an influence upon the color and stability of the 

 product, but it is to be noticed that only one eighth of the 



Am. Jour. Sci.— Third Series, Yol. XLY, No. 273.— Sept., 1893. 

 14 



