162 Oooch and Fairbanks — lodometric Estimation^ etc. 



fifteen minutes, but for complete oxidation the trapped or 

 corked bottle should be set aside out of sunlight for an hour 

 and a half or two hours. The iodine which was not used for 

 reoxidation was then titrated with a standard arsenic solution. 

 Since there is a slight tendency, especially when sodium 

 hydroxide and acid sodium carbonate are used for neutraliza 

 tion, toward the formation of a little iodate, it is wise to acidu- 

 late the solution in each case slightly with dilute hydrochloric 

 acid and then to determine by sodium thiosulphate the iodine 

 which has taken the form of iodate. The ratio 126'85:144: 

 expresses the relation of the total amount of iodine used in 

 the reoxidation process to the calculated amount of molybdic 

 acid present. The table given below shows the amount of 

 molybdic acid taken in the form of ammonium molybdate and 

 the molybdic acid found calculated from the iodine used in 

 reoxidation. 



1 



M0O3 as 













ammonium 





M0O3 









molybdate. 



KI. 



found. 



Error. 



Neutralized by 



grm. 



grm. 



grm. 



grm. 







1640 



•5 



•1639 



0001- 



K,,C03 + NaHC03 



1692 



•5 



•1681 



0011- 



(( 



a 



1666 



•5 



•1661 



•0005- 



(£ 



a 



1517 



•5 



•1517 



0000 



NaHCO, 



2530 



•5 



•2537 



•0007 + 



a 





1636 



•5 



•1637 



•0001 + 



n 





1702 



•5 



•1702 



•0000 



a 





1520 



•5 



•1518 



•0002- 



ti 



^ 



1642 



•5 



•1652 



•0010 + 



it 





4560 



•75 



•4560 



•0000 



u 







1690 



•5 



•1683 



•0007- 



NaOH + NaHCO, 





0507 



•5 



•0519 



•0012 + 



a 



(£ 





1663 



•5 



•1666 



0003 + 



a 



(I 





0101 



•5 



•0095 



•0006 — 



u 



iC 





1639 



•5 



•1632 



0007- 



i( 



a 





1636 



•5 



•1625 



0011- 



<( 



i( 





0507 



•5 



•0510 



0003 + 



(( 



ic 





1685 



•5 



•1683 



0002- 



i( 



i( 





1514 



•5 



•1512 



0002 — 



u 



it 



•1649 



•5 



•1646 



0003 — 



« 



li 





^Lverage 



error in 



the experim 



ents, — 



•0001 gram. 





The results given in the foregoing table show that molybdic 

 acid can be determined with accuracy and convenience by boil- 

 ing it with hydrochloric acid and a small excess of potassium 

 iodide to a definite concentration in an ordinary flask, then 

 neutralizing the residue with acid sodium carbonate, and reoxi- 

 dizing the reduced molybdic acid with standard iodine. 



