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INDIANA UNIVERSITY 



The best conditions, when using barium selenate, were found 

 to be: 



(1) 2.8 grams ''ammonium carbonate" to one gram barium 

 selenate, which is about five molecules of carbon dioxide to one 

 molecule of barium selenate. 



(2) 10 cc. of water to each gram of barium selenate. 



(3) The mixture should stand about thirty hours, with occa- 

 sional shaking. 



Increase of temperature, stirring with air or carbon dioxide, or 

 carrying out tlie reaction in sealed tubes does not increase the 

 }deld. 



The best conditions, when using lead selenate, are : 



(1) 0.55 gram "ammonium carbonate" to one gram of lead 

 selenate, which is about 1.24 molecules of actual carbon dioxide to 

 one molecule of lead selenate. 



(2) 5 cc. water to each gram of lead selenate. 



(3) The mixture should stand about one or two hours to get 

 the best yields, although good yields may be obtained in fifteen to 

 thirty minutes. 



The results of these experiments show that lead selenate is 

 the better material to use, because (1) it is more easily prepared, as 

 the precipitate is more easily filtered and washed; (2) it gives a 

 better yield and requires less "ammonium carbonate" and less time 

 than does barium selenate. 



