﻿56 



IXDTAXA UNIVEESITY 



Results with Lead Selenate : Assuming the reaction 



PbSeO,+ (NH,),CO, ^ PbCCv, + (NHJ.SeO^ 



one gram of lead selenate is equivalent to 0.2744 gram ' ' ammonium 

 carbonate." In the following tables 0.27 gram ''ammonium car- 

 bonate" represents 0.62 molecules of carbon dioxide to 1 molecule of 

 lead selenate; 0.55 gram ''ammonium carbonate" represents 1.24 

 molecules of carbon dioxide to 1 molecule of lead selenate and 1.1 

 grams "ammonium carbonate" represent 2. 48 molecules of car- 

 bon dioxide to 1 molecule of lead selenate. 



Table I. 



Amount of 

 Ammon. Carb. 



Amount of 

 Lead Seleu. 



Amount of 

 Water. 



Time 

 Treated. 



Yield 

 Per Cent. 



0.274 



gram 



1 



gram 



10 



cc. 



0.5 



hr. 



47.20 



0.274 



gram 



1 



gTam 



10 



cc. 



1 



nr. 



48.72 



0.274 



gram 



1 



gram 



10 



cc. 



2 



hrs. 



50.45 



0.274 



gram 



1 



gram 



10 



cc. 



4 



hrs. 



53.71 



0.274 



gram 



1 



gram 



10 



cc. 



6 



hrs. 



55.31 



0.274 



gram 



1 



gram 



10 



cc. 



8 



lirs. 



56.79 



0.274 



gram 



1 



gram 



10 



cc. 



12 



hrs. 



56.79 



0.274 



gram 



1 



gram 



10 



cc. 



24 



hrs. 



58.59 



0.55 



gram 



1 



gram 



5 



cc. 



0.5 



hr. 



94.32 



0.55 



gram 



1 



gram 



5 



cc. 



1 



hr. 



94.32 



0.55 



gram 



1 



gram 



5 



cc. 



3 



hrs. 



98.46 



0.55 



gram 



1 



gram 



5 



cc. 



16 



hrs. 



97.65 



0.55 



gram 



1 



gram 



5 



cc. 



22 



hrs. 



99.28 



0.55 



gram 



1 



gram 



5 



cc. 



28 



hrs. 



97.65 



0.55 



gram 



1 



gram 



5 



cc. 



30 



hrs. 



97.65 



1.10 



gram 



1 



gTam 



10 



cc. 



0.5 



hr. 



96.02 



1.10 



gram 



1 



gram 



10 



cc. 



1 



hr. 



96.02 



1.10 



gram 



1 



gram 



10 



cc. 



4 



hrs. 



96.02 



1.10 



gram 



1 



gram 



10 



cc. 



0.25 



hr. 



96.02 



1.10 



gram 



1 



gram 



5 



cc. 



1 



hr. 



93.58 



1.10 



gram 



1 



gram 



5 



cc. 



2 



hrs. 



96.02 



1.10 



gram 



1 



gram 



5 



cc. 



6 



hrs. 



96.02 



1.10 



gram 



1 



gram 



"5 



cc. 



24 



hrs. 



96.02 



This table shows that it is necessary to use 1.2 molecules of 

 ' ' ammonium carbonate " to 1 molecule of lead selenate, and that the 

 reaction takes place comparativel}^ rapidly. The change of dilution 

 from five cc. to ten cc. is apparently of no effect as long as there is 

 an excess of "ammonium carbonate." 



Experiments not given here show that stirring with air or con- 

 tinually shaking is of no advantage, as there is little if any change 

 in the yield. 



