122 PROCEEDINGS OF THE AMERICAN ACADEMY. 



lime. This treatment is of course more thorough and satisfactory than 

 Stag's method of digesting them with hydrochloric acid. The silver was 

 subsequently treated with ammonia, thoroughly washed with water, and 

 dried in a desiccator over soda lime. One large piece was rolled out be- 

 tween clean steel rollers ; and the foil, after having been cut into small 

 strips, was cleansed as above described. These fragments made it pos- 

 sible to weigh out any desired amount of the metal. 



Bromine was prepared in common with Mr. Cushman. For the 

 method used the paper upon nickel should be consulted. Much ex- 

 perience has led to the conclusion that the method there described is the 

 most satisfactory and convenient means of obtaining pure bromine, since 

 it eliminates organic as well as iuoi'ganic impurities. In order to test 

 the purity of the bromine and silver, 2.18679 grams of silver (in vacuum) 

 were dissolved in pure nitric acid and precipitated with a slight excess of 

 ammonic bromide which had been prepared by running the bromine in 

 question into [)ure ammonia. The silver bromide was collected on a 

 Gooch crucible and afterwards fused in a porcelain crucible. The fused 

 bromide weighed 3.80679 in vacuum, whence the ratio of silver bromide to 

 silver is 100.000 : 57.444. Mr. Cushman, experimenting upon the same 

 sample of bromine, obtained the result 57.445; and since Stas's result 

 was identical with these, there can be no doubt of the purity of our silver 

 and bromine. 



The sulphuric acid used in the drying towers was boiled for some time 

 in order to increase its efficiency and to free it from volatile impurities. 

 The phosphoric oxide was proved free from volatile compounds of phos- 

 phorus by passing a current of air over a considerable quantity of this 

 substance into aqua regia for several hours. The aqua regia was sub- 

 sequently found to contain no phosphorus. Distilled water was pre- 

 pared with all the usual precautions necessary to free it from organic 

 and non-volatile impurities, as well as from ammonia ; nitric and hydro- 

 bromic acids were purified by repeated distillation with a platinum con- 

 denser ; great care was taken to exclude dust, as well as the products of 

 the combustion of illuminating gas, from the substances under treatment; 

 platinum vessels were employed wherever it was possible to employ 

 them ; and many other precautions, often essential in order to prevent 

 the complicated processes from introducing as much impurity as they 

 removed, were applied. Alkali metals and silica, it will be seen, were 

 among the impurities avoided as much as possible. For several pieces 

 of platinum ware and other apparatus we are indebted to the Cyrus M. 

 Warren Fund for research in Harvard University. 



