452 Gooch and Pulman — Estimation, of Molybdic Acid. 



separating-funnel to serve for the gradual introduction of 

 reagents, and to the outlet tube a "Will and Varrentrapp bulbed 

 tube charged with a solution of potassium iodide to catch any 

 traces of iodine thrown off mechanically during the process of 

 neutralization to follow. Through the separating funnel were 

 then added 0*5 grm. of manganese sulphate, and from a 



71 



burette an approximately — solution of potassium perman- 

 ganate of known value until the characteristic color was given 

 to the solution, the amount of permanganate thus added 

 being noted. Then, from a burette, was added enough of a 

 standard arsenite solution to correspond approximately to the 

 value of the permanganate used ; experience having shown 

 that this amount of arsenite is sufficient to reduce with readi- 

 ness in the acid solution the iodic acid, the permanganate, 

 the higher oxides of manganese, and nearly all the free iodine, 

 the remainder of the last being taken up immediately after 

 the subsequent neutralization. The amount of this solution 

 was noted. Next a solution of about 3 grm. of tartaric acid 

 was run in, and the free acid of the solution was neutralized by 

 acid potassium carbonate. This accomplished, the liquid ad- 

 hering to stopper and tubes was washed off into the bottle, the 

 contents of the trap added, and the residual arsenite was 

 titrated by standard iodine, using the starch indicator. 



The results of experiments are given in the following table : 



Weight of Weight of Weight of 



Mo0 3 taken KL used M0O3 



as ammonium found. Error, 



molybdate. 



grm. grm. grm. grm. 



0-0423 0*2 0-0430 0*0007 + 



0-0429 0-2 0-0435 0*0006 + 



0-0420 0-2 0-0427 0*0007 + 



0*0827 0-3 0-0829 0*0002 + 



0-0837 0*35 0-0838 0*0001 + 



0*0826 0-5 0-0832 0*0006 + 



0*2465 0*6 0*2460 ' 0*0005 — 



0*2481 0*6 0*2469 0.0012 — 



0*2470 0*6 0*2465 0*0005 — 



It is plain that molybdic acid may be determined with accu- 

 racy by reduction under the prescribed conditions with potas- 

 sium iodide and hydrochloric acid, treatment of the residue 

 with manganous sulphate, standard potassium permanganate, 

 standard arsenic, and, after addition of tartaric acid and 

 neutralization, titration with iodine. When many determina- 

 tions are to be made the process will yield results with rapid- 

 ity, because as many operations can be started successively in 

 the Erlenmeyer flasks as an operator can handle with con- 

 venience, a simple neutralization bottle serving for the treat- 

 ment of all the reduced residues as they come along. 



