RICHARDS. ATOMIC WEIGHT OF BARIUM. 



83 



the third was as much as 34 milligrams. This change was probably 

 due to the fact that the argentic chloride produced by the successive 

 additions of the solutions was of the more soluble flaky variety, while 

 the greater part of the precipitate had been so thoroughly shaken be- 

 fore as to become much less soluble. A larger amount of the salt in 

 solution naturally required more of each reagent to precipitate it. 

 This phenomenon was the chief cause of uncertainty in the attempt to 

 confirm Stas's results. Probably the reason for his overlooking it lay 

 in the fact that he rarely titrated backward and forward many times 

 with the same solution. 



In the experiments tabulated below, the baric chloride was ignited 

 in the air, and the small amount of chlorine lost was allowed for as 

 usual. The calculated and carefully weighed amount of pure silver 

 was dissolved in nearly three times its weight of the purest nitric acid 

 in a Bohemian flask provided with bulb tubes for arresting the spray. 

 The bulbs were washed out into the flask, the nitrous fumes were 

 expelled by heating upon the steam bath for a long time, the con- 

 tents of the flask were diluted and cooled, and the argentic nitrate 

 was added to the baric chloride in a glass-stoppered flask. 



In every case the first readings of the end-points are recorded in 

 the table as being the most trustworthy, although in some cases as 

 much as three weeks were spent upon a single determination in titrat- 

 ing backward and forward. The weights are, as usual, reduced to the 

 vacuum standard. 



RATIO OF SILVER TO BARIC CHLORIDE. 

 First Series: Stas's Second Method. 



