52 



J. T. Norton, Jr. — Titration of Mercury 



titrated with iodine and starch solution. The duration of the 

 process need not exceed 15 minutes. It is worthy of note 

 that there is no necessity of using any hydrochloric acid in 

 addition to that formed in the reaction. This certainly elimi- 

 nates one probable source of error — the interaction of hydro- 

 chloric acid and sodium thiosulphate. 



In dealing with the estimation of mercury in the form of 

 mercurous nitrate the same method of procedure was emplo} T ed 

 as in the case of mercuric chloride. A solution of mercurous 

 nitrate was prepared by dissolving as much as possible of 20 

 grams of the salt in about 200 om3 of water, filtering off the 

 clear liquid and diluting to a definite volume. The standard 

 of the solution was determined by precipitation as metallic 

 mercury by means of the electric current. Contrary to the 

 statement made in Sutton, the brown precipitate of Hg s S — 

 formed as shown in the equation, 



Hg 2 (N0 3 ) 2 + Na 2 S 2 O s = Hg 2 S + Na 2 S0 4 -f-N 2 - 



does not settle and leave a clear supernatant liquid, but the 

 solution remains cloudy and it is impossible to see any end 

 reaction. Although the conditions of dilution, temperature 

 and amount of acid present were carefully considered, no 

 arrangement or adjustment of these conditions was found 

 under which satisfactory results could be obtained. Table V 

 gives the result of experiments. 











Table V. 











Hg a (N T O s ) a 





Volume 







Hg 2 (NO s ) 2 







taken 



HN0 3 



at 



Tem- 



Na 2 S 2 2 



found 







as Hg. 



1: 3. 



beginning. 



perature. 



in excess 



as Hg. 



Error. 





grams. 



cm 3 . 



cm 3 . 



C. 



cm 3 . 



grams. 



grams 



1. 



0-0148 



none 



50 



50° 



4-28 



0-0129 



0-0019 



2. 



0-0148 



a 



75 



60 



4-45 



0-0117 



0-0031 



3. 



0-2976 



u 



300 



60 



12-67 



0-2760 



0-0216 



4. 



0-1488 



a 



100 



40 



2-19 



0-1386 



0-0102 



5. 



0-1488 



i< 



100 



50 



6-92 



0-1378 



o-ono 



6. 



0-1488 



a 



200 



50 



0-78 



0-1388 



o-oioo 



7. 



0-0744 



a 



100 



65 



0-73 



00636 



00108 



8. 



0-0744 



1 



100 



55 



0-49 



0733 



o-oon 



9. 



0-0744 



2 



100 



40 



1-16 



0-0660 



0-0084 



10. 



0-0744 



1 



100 



55 



1-35 



0-0685 



0-0059 



11. 



0-0744 



1 



100 



55 



0-S2 



0-0686 



0-0058 



12. 



0-0744 



1 



200 



55 



1-71 



0-0685 



0-0059 



13. 



0-0744 



4 



100 



40 



1-77 



0-0649 



0-0095 



14. 



0-0744 



5| 



100 



40 



1-34 



0-0645 



0-0099 



15. 



0-0744 



' 1 



100 



45 



1-71 



0-0654 



0-0090 



16. 



0*0744 



10 



100 



45 



1-55 



0-0669 



0-0075 



17. 



0-1488 



1 



100 



40 



0-73 



0-1391 



0-0097 



