Determination of Molybdenum. 



175 



KI 



taken, 

 grm. 



Vol. ' 

 cm 3 . 



Percentage 



of HCl in 



aqueous 



acid. 



Concentra- 

 tion by- 

 boiling 

 cm 3 . 



Mo0 3 equiv- 

 alent to 

 iodine found. 



grm. Remarks. 



1 



40 



24 



( 40-30 

 ( 30-20 



0-0013 

 0-0002 



Iodine determined 



in distillate. 

 1 grm. of KI added 



1 



40 



20 



40-25 



0*0005 



to retort at the 

 beginning of the 

 2d stage. 

 The acid taken, sp. 

 gr. l'J,was freshly 

 boiled and intro- 

 duced at once up- 

 on KI in retort in 

 CO,. 



It is obvious that the procedure recommended by Friedheim 

 and Euler can by no possibility eliminate the effect of atmos 

 pheric action upon the mixture of acid and iodide. The ex- 

 tent of such action must depend upon such conditions as the 

 size of the apparatus, the time of exposure, the body of air 

 above and dissolved in the liquid, and the rate of displacement 

 of the air. How great the error due to atmospheric action 

 actually was in the process as conducted by Friedheim and 

 Euler we, of course, have no means of knowing. It is to be 

 hoped, however, that it was sufficiently great to counterbalance 

 that other inevitable error (of about five milligrams) which 

 exists by reason of the incompleteness with which molybdic 

 acid is reduced under the conditions which these investigators 

 prescribe; for, the value of Enlers work upon the vanadio- 

 molybdates rests upon the chance that these two very consider- 

 able and indisputable tendencies to error may have neutralized 

 one another. 



It has been shown clearly that our former criticism of the 

 procedure of Friedheim and Euler is justified in every par- 

 ticular. We have no change to make in the recommendation 

 made therein as to necessary modifications. 



If the conditions seem difficult, there is an alternative in the 

 method proposed in the former article*, according to which 

 the molybdate is reduced by the acid and iodide in an Erlen- 

 meyer beaker (trapped loosely by means of a short bulbed 

 tube hung in the neck) and the molybdenum pentoxide, freed 

 from iodine by boiling, is reoxidized by standard iodine in 

 alkaline solution. 



This Jour. IV, ii. 156. 



