IOWA ACADEMY OF SCIENCES. 



131 



In comparing the conductivity of the double salt with 

 the sum of the conductivities of the constituents twice the 

 molecular conductivity of sodium bromide at one-half the 

 dilution of the double salt is taken To this is added three 

 times the molecular conductivity of cadmium bromide at 

 one-third the dilution of the double salt. The reason for 

 this is apparent from the composition of the double salt. 



Comparison for 2NaBr, 3CdBr^. 



Volume. 



Differ- 

 ence. 



2.443 

 4.886 

 9.772 

 19.544 

 39.088 

 4S.86 

 97.72 

 195.44 

 390.88 

 781.76 

 1563.53 

 3908.8 

 7817.6 



82 9 

 77.4 

 73 4 

 66.1 

 63 1 

 62.4 

 62.6 

 57.4 

 53.4 

 52.9 

 43 5 

 37.8 

 33.0 



A NEW DOUBLE BROMIDE OF AMMONIUM AND ZINC. 



3 NH, Br, Zn Biv 



The constituent bromides were brought together in the 

 proportion to form the double bromide 2 NH4 Br. ZnBr., 

 H„o as described in the literature. After about two mouths 

 100 grams of a well crystallized salt were obtained, and 

 this was analyzed. One anaysis showed the salt to contain 

 12.8 per cent, of zinc, and a second analysis gave 12.6 per 

 cent. The per centage of zinc in the salt 2NH4Br, ZnBr^ 

 H„o is 14.9. It was concluded that either there was present 

 a second double salt containing more than two molecules 

 of ammonium bromide to one of zinc bromide, or that 

 ammonium bromide had crystallized out along with the 

 double salt. A careful examination of the crystals showed 

 that some were apparenty of different habit from the 



