410 PROCEEDINGS OF THE AMERICAN ACADEMY. 



added through a funnel with a long fine stem which extended through 

 the column of bulbs nearly to the bottom of the flask. After the ad- 

 dition of the hydrazine, the reaction was allowed to continue slowly, 

 with occasional shaking, and was completed by heating the solution 

 upon a steam bath for a short time. In the presence of acid a dilute 

 solution of hydrazine is without effect upon silver salts. 



After the solution had been allowed to cool, it was diluted to a 

 volume of one and one half liters, and the silver was precipitated as 

 chloride or bromide by the addition of a very dilute solution of an ex- 

 cess of either hydrochloric or hydrobromic acid. The flask with its 

 contents was shaken thoroughly for a few moments and was then 

 allowed to stand several days, until, the silver bromide having settled, 

 the supernatant solution was perfectly clear. 



Since the mother liquor of the silver halide contained both nitric and 

 hydrobromic acids in excess, the use of a Gooch-Munroe-Neubauer 

 crucible seemed to be attended with danger on account of solution of 

 platinum. Such a possibility has already been pointed out, 27 and an 

 actual loss was found to take place in blank experiments carried out 

 at the beginning of this research. Accordingly the ordinary platinum 

 Gooch crucible with an asbestos mat was used. The asbestos had been 

 carefully prepared by ignition, and washing first with nitric acid and 

 then with water. The crucible was prepared for weighing before and 

 after filtration of the silver halide in exactly the same way. 



The silver halides were washed many times by decantation with 

 dilute hydrochloric acid in the case of silver chloride, and with very di- 

 lute hydrobromic acid in the case of silver bromide. The precipitate 

 was then transferred to the weighed crucible and was dried in an elec- 

 tric oven at 170° for at least sixteen hours. 



In order to correct for the small quantity of moisture retained by 

 the silver halides, each precipitate was transferred as completely as 

 possible to a porcelain crucible and fused. From the loss of weight of 

 the portion of silver salt transferred to the crucible, the amount of 

 water in the entire precipitate was calculated. 



The small quantity of asbestos, together with a trace of silver bro- 

 mide which escaped the crucible, was collected by passing the entire 

 filtrate and washings through a small filter. The ash of this filter was 

 treated with nitric and with hydrochloric or hydrobromic acids, then it 

 was reheated and the crucible was weighed. After correction for the 

 ash of the filter, the gain in weight of the crucible was added to the 

 weight of the main mass of silver halide. 



27 Morse, " Exercises in Quantitative Chemistry," p. 203 (1905). 



