360 Browning and Goodman — Estimation of Vanadium. 



but in the use of citric acid it is advisable to avoid a large 

 excess, which tends to give high results. Accordingly in the 

 following series of experiments it will be noticed that the 

 amounts of citric acid do not exceed two grams except where 

 ammonium molybdate or sodium tungstate are present, when 

 the ammonium or sodium base combines with part of the free 

 acid. The results follow : 











Sodium 











Ammonium tung. 



V2O5 taken. 



Y2O5 found. 



Error. 



Citric acid. 



molybdate. state. 



grm. 



grm. 



grm. 



grm. 



grm. grm. 



(1) 0-1956 



0-1956 



o-oooo± 



1 





(2) 0-3905 



0-3921 



0-0016 + 



2 





(3) 0-1960 



0-1960 



o-oooo± 



1 





(4) 0-1953 



0-1960 



0-0007 4- 



1 





(5) 0-2088 



0-2082 



0-0006 — 



2 





(6) 0-2100 



0-2098 



0-0002- 



2 





(7) 0-2092 



0-2107 



0-0015 + 



1 





(8) 0-2092 



0-2107 



0-0015 + 



2 





(9) 0-2096 



0-2082 



0-0014 — 



2 



0-5 



(10) 0-2099 



0-2116 



00017 + 



3 



0-5 



(11) 2005 



0-2101 



0-0006 + 



2 



05 



(12) 0-2099 



0-2095 



0-0004 — 



3 



0-5 



The mode of proceeding in the estimation of vanadium by 

 the use of either tartaric, oxalic or citric acids maj be briefly 

 summarized as follows: To a solution of a vanadate with or 

 without a tungstate or molybdate, add approximately one 

 gram of the acid for every tenth of a gram of substance to be 

 determined. Heat the solution to boiling, except in case tar- 

 taric acid be present with molybdic acid, when digestion for 

 from fifteen to twenty-four hours in the cold should be substi- 

 tuted. To the cold liquid add about five grams of potassium 

 bicarbonate for every gram of acid used. Add iodine in slight 

 excess and set aside until no further bleaching is noticeable. 

 Destroy the excess of iodine with arsenious oxide solution, add 

 starch, and titrate back with standard iodine. The total 

 amount of iodine used less the equivalent of the arsenious 

 oxide is the measure of the oxidation. 



I have found it of advantage, when starting with a new solu- 

 tion of the vanadate, to make one determination roughly and to 

 get from this rough determination the proportions of acid and 

 iodine to be used in the determinations to follow. Large 

 amounts of the acid and a large excess of the iodine have been 

 employed in many determinations without any apparent unfav- 

 orable effect upon the results. The tendency, however, under 

 these circumstances is toward plus errors, which may be 

 avoided by following the above directions. 



June, 1896. 



