184 
IOWA ACADEMY OF SCIENCES. 
being true in a more pronounced degree in the case of the 
bromide and the iodide. The iodide in some cases is but 
one-twentieth the amount called for. 
Cohen * has called in question Valenta’s results in two 
particulars. In the case of the chloride he claims that if 
the thiosulphate solution is agitated with a large excess of 
AgCl, a slightly soluble salt (Ag S 2 0 3 Na) 2 is formed which 
separates out. He submits experimental results of his own, 
supporting his theory and implies that the same is true for 
the iodide and bromide. He questions whether Yalenta 
obtained saturation in the case of the last two salts. It 
seemed desirable, therefore, to study the solubility of the 
iodide, at least, and the effect of temperature upon the 
solubility of the bromide as well as the iodide. It seemed 
probable that some light upon the complexes formed might 
be gained by using some insoluble salt of silver whose acid 
radical was very different from the closely similar chlorine 
bromine and iodine, and for this salt silver iodate was 
chosen, which so far as known to me has not been studied 
with reference to its action on thiosulphates. 
Richards and Faberf made determinations of the solu- 
bility of silver Bromide in sodium thiosulphate solutions 
of varying concentration, also making a few determinations 
with silver chloride, in all cases working at a temperature 
of 85°. Valenta’s experiments were made apparently at 
room temperature. 
For the determinations of the iodide, pure silver iodide 
was prepared by precipitating a solution of pure silver 
nitrate with an excess of pure potassium iodide solution. 
The precipitate was thoroughly washed and dried at 150°, 
Solutions of known strength of sodium thiosulphate were 
made by dissolving weighed amounts of the pure recrys- 
tallized salt in recently boiled water, a fresh solution being 
used in each experiment. An excess of the Agl was placed 
in the thiosulphate solution in a tightly closed tube and 
agitated for several hours, the temperature at first being 
kept several degrees above that at which solubility was to 
•Zeit. Phys. Chem. 18:61. 
•hAm.Chem. Jo. 21 :-167 . 
