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IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
Later some important work was done on these compounds and 
others by Kremers, 3 Grotian 4 and Berthelot. 5 The latter gave 
us the general proposition founded upon his thermochemical 
studies: “Double salts formed with the liberation of a small 
amount of heat are to be regarded as separated, for the most 
part, into their constituents, by water.” 
In 1910 Parsons and Evans 6 made a thorough- study of the 
alums, including in their investigations : 
Ammonium Chrome Alum. 
Potassium Chrome Alum. 
Potassium Aluminium Alum. 
Ammonium Aluminium Alum. 
Ferric Ammonium Alum. 
In summing up the results obtained from their study, the 
authors said, in a paper presented before the American Chem- 
ical Society: “When alums are dissolved in water they are 
decomposed into the simple sulphates which can be separated 
from each other by diffusion. The Chrome Alums separate 
more readily than the Aluminium Alums,” 
Jones and Ota 7 used the conductivity method in determining 
the presence of double salts and by increasing the dilution they 
were able to determine the rate of dissociation. The work in- 
cluded the study of four double chlorides and those at only a 
small range of dilution. The same method was employed by 
Jones and Knight 8 in a comprehensive study of the double bro- 
mides and chlorides. This work included many more double salts 
than had been studied before and each one was measured over a 
much wider range of dilution. In several salts the dilution ranged 
from the molecular weight in two litres to the same in seventeen 
thousand litres. An important part of this work was the dis- 
covery of two new double bromides : sodium cadmium bromide 
and ammonium zinc bromide. These new salts were analyzed 
and found to have the composition : 2NaBr. 3CdBr 2 -|-6fLO and 
3NH 4 Br. ZnBr 2 . 
3 Ann. Fhys. (Pogg), 98, 58. 
4 Ann. Phys. (Wied), 18, 177. 
5 Ann. Chim. Phys. (5), 29, 198. 
e Journal of the Amer. Chem. Soc., Vol. 32, page 1383, 1910. 
7 Amer. Chem. Journal, 22, 5. 
8 Amer. Chem. Journal, Vol. 21, No. 2, August, 1899. 
