314 D. L. Randall — Behavior of Molybdic Acid. 







Table I. 







KMn0 4 



KMn0 4 





?eS0 4 



used 



theory 



Difference 



cm 3 . 



era 3 . 



cm 3 . 



cm 3 . 



20 



24-45 



23-25 



1-20 



20 



23-88 



23-25 



•63 



20 



25-40 



23 25 



2-J5 



20 



24-90 



23-25 



1-65 



This excessive reducing action on the permanganate must be 

 due either to impurities in the zinc, to small particles of zinc 

 worked through the asbestos layer at the bottom of the reduc- 

 tor, or possibly to the hydrogen formed in the rednctor. That 

 the last mentioned possibility is a sufficient cause of the effects 

 obtained was shown by passing hydrogen, formed by the action 

 of hydrochloric acid on zinc in a Kipp generator and washed 

 with water and caustic potash, through 23 cm3 standard perman- 

 ganate diluted with 300 cm3 of hot dilute (2 - 5 per cent) sul- 

 phuric acid, adding 20 cmS of a solution of standard ferrous 

 sulphate and titrating back with permanganate. The results 

 obtained by such action of hydrogen during fifteen minutes is 

 shown in Table II. 





Table II. 





FeS0 4 

 cm 3 . 



KMn0 4 



required 



cm 3 . 



KMn0 4 



theory 

 cm 3 . 



Eeduced by 



hydrogen 



cm 3 . 



20 



24-6 



23-1 



1-5 



20 



24-7 



23'1 



1-6 



20 



23-6 



23- L 



•5 



Having seen that potassium permanganate could not be used 

 in the reductor flask, ferric alum was next tried as 'an oxidizer. 

 The only objection to the use of this salt, that at the usual 

 dilution of 500-600 cm3 an excess of ferric alum colors the solu- 

 tion strongly and makes the end point in the titration some- 

 what difficult to recognize, is overcome by the addition of a 

 few centimeters of phosphoric acid which renders the solution 

 colorless. 



For the work with the ferric oxidizer the C. P. ammonium 

 molybdate of commerce was recrystallized and found to contain 

 81-55 per cent of molybdenum trioxide by treating weighed 

 portions in a platinum crucible with nitric acid and evaporating 

 to dryness on the steam bath and igniting gently and weighing 

 the molybdic anhydride formed. The ferric iron solution for 

 use in the reductor flask was prepared by dissolving 100 grams 

 of the crystalized salt in one liter of water. The column of 

 zinc in the reductor was 36 cm in length. The procedure was 

 to charge the reductor flask with 20 or 30 cm3 of the iron solu- 

 tion and 4 cm3 of phosphoric acid and to pass through the reduc- 



