426 PROCEEDINGS OF THE AMERICAN ACADEMY. 



was done by passing the entire filtrate and wash waters through a small 

 filter paper. The paper was ignited in a weighed porcelain crucible, 

 and the ash was treated with nitric acid and then hydrobromic acid to 

 convert a trace of reduced silver to the state of bromide. In order to 

 avoid any danger from adsorption of chromic salts by the filter paper, 

 at the end of the filtration the paper was rinsed with hot dilute hydro- 

 bromic acid. The correction for asbestos could have been avoided if it 

 had been possible to employ a Gooch-Munroe-Neubauer crucible with 

 a mat of platinum sponge. It has already been shown, however, in the 

 preceding paper, 6 that such crucibles lose markedly in weight when ex- 

 posed to the action even of the dilute aqua regia of the mother liquors 

 of these analyses. 



The moisture retained by the silver bromide was found by fusing the 

 dried salt in a porcelain crucible, the loss in weight on fusion being de- 

 termined. The fused silver bromide was always light yellow and gave 

 every indication of purity. 



As in the preceding research a small quantity of silver bromide dis- 

 solved in the filtrate and wash waters was found by evaporating the 

 combined filtrate and wash waters until nearly all the excess of acid 

 had been expelled, and then, after slight dilution, precipitating the sil- 

 ver as sulphide. The 'sulphide was collected on a small paper, the ash 

 of which, after ignition, was treated with nitric acid. The amount of 

 silver thus obtained was found by comparison in a nephelometer of pre- 

 cipitates of silver bromide produced in this solution and in very dilute 

 standard solutions of silver. 



In Analysis 9 the silver was precipitated as silver chloride, the only 

 other difference in the procedure being that the precipitate was washed 

 with dilute hydrochloric acid instead of pure water. 



The Determination of Moisture and Nitric Acid in Silver 



DlCHROMATE. 



Silver dichromate which has been crystallized from nitric acid, after 

 being dried at 200°, contains traces of both nitric acid and water. Both 

 of these substances can be expelled from the salt by fusion, although 

 slight decomposition of the salt takes place simultaneously. Since the 

 only readily volatile substance which can be formed by the decomposi- 

 tion of the salt is oxygen gas, the problem of the determination of the 

 moisture and nitric acid consisted in that of absorbing in a quantitative 

 fashion the water, nitric acid, and nitric peroxide formed by decomposi- 



6 Baxter, Mueller, and Hines, loc. cit. 



