160 Gooch and Fairbcmks — lodometric 



MoOa dissolved 









in NaOH. 



KI. 



M0O3 found. 



Error. 



grm. 



grm. 



grm. 



grm. 



•2273 



0-5 



•2281 



•0008 + 



•2052 



0-5 



•2062 



•0010 + 



•3474 



0-5 



•3467 



•0007 — 



III. Reoxidation Process. — It was noticed during our 

 experiments upon the method of Mauro and Danesi, as has 

 been remarked previously, that large amounts of iodine in the 

 digestion flask seemed to react upon the reduced product. In 

 the process of Friedheim and Euler, too, it was discovered that, 

 when the iodine which had collected in the second flask was 

 drawn back into the first flask and mixed with the hot reduced 

 product, the iodine found by titration was deficient in amount. 

 It was found also that small amounts of standard iodine, intro- 

 duced into the flask containing the reduced molybdic acid in 

 an atmosphere of carbon dioxide, were absorbed slowly when 

 this mixture was heated. This slow disappearance of the 

 iodine in acid solution suggested the possibility of effecting 

 the complete oxidation of the reduced molybdic acid in an 

 alkaline solution, containing a tartrate or other salt of an organic 

 acid to prevent precipitation. Several experiments were made 

 in this direction upon the residues left in the process of Fried- 

 heim and Euler, the distillate having been titrated as usual 

 with sodium thiosulphate to make sure that the reduction had 

 proceeded properly. These residues were treated in each case 

 with 1 grm. of tartaric acid, neutralized by acid sodium car- 

 bonate and left standing for an hour or two with an excess of 

 standard iodine. Upon determining, by means of standard 

 arsenious acid, the iodine left over, it was found that the amount 

 of it which had disappeared corresponded very closely with 

 that set free in the distillation, which is of course the same as 

 that necessary to reoxidize the molybdic acid completely. 



The conditions necessary to complete oxidation being known, 

 experiments were made to see whether the process could not 

 be successfully carried on in an open flask. Naturally under 

 these conditions the air present must, as in the previous experi- 

 ments, tend to set free some iodine at the outset, but, inasmuch 

 as the hydriodic acid gradually diminishes in strength as the 

 molybdenum is reduced and all iodine is ultimately driven 

 from the flask, which is filled with steam during the boiling, it 

 seemed possible that the danger from the action of atmo- 

 spheric oxygen might be so far reduced as not to interfere 

 essentially in the estimation of the molybdenum in the residue, 

 provided the contents of the flask is diluted and cooled at the 

 end of the boiling. Ammonium molybdate containing from 

 0*1 to 0*3 grm. molybdic acid, 0*5 grm. of potassium iodide, 



