W. A. Turner — Vanadium Determined hy Cupferron. 341 



The determinations by means of the cupferron solution 

 were carried out as follows : 



Portions of about twenty-five cubic centimeters of the meta- 

 vanadate solution, accurately weighed, were diluted to about 

 150-200 cm 3 . The hydrochloric acid present in the metavana- 

 date solution was sufficient for the complete precipitation of 

 the vanadium. Not more than 1 per cent acid content (hydro- 

 chloric or sulphuric) is needed. Cupferron solution (6 per 

 cent) prepared according to Baudisch* was then added with 

 stirring until a slight excess was present as shown by the 

 appearance of a white precipitate of nitrosophenylhydroxy- 

 lamine (formed when cupferron comes in contact with an acid 

 solution). Two or three cubic centimeters in excess are added 

 and the precipitate is filtered on paper without delay and 

 washed with a 1 per cent solution of sulphuric acid containing 

 a little cupferron. The precipitate after being allowed to 

 drain on the filter for a time is transferred with the paper to a 

 platinum crucible, dried, ignited and weighed as vanadium 

 pentoxide. 



In this process there are several precautions which should be 

 observed. The precipitate after being filtered on paper is 

 transferred to a large platinum crucible and heated with a 

 small flame to dry the mass and remove volatile substances 

 from the precipitate and paper. This should be done cau- 

 tiously in order not to produce a heat sufficient to fuse the 

 vanadium oxide. If the attempt is made to hasten the ignition, 

 the carbon of the unburned filter may mingle with the fused 

 vanadium oxide, thus delaying the oxidation of the former, 

 which is ultimately accomplished probably more or less at the 

 expense of the latter. At best some of the oxide is likely to 

 become reduced and must be thoroughly exposed to the action 

 of the air by revolving the crucible held by the tongs in the 

 flame and allowing the fused oxide to flow on the sides. By 

 this means the oxide may be brought to its highest state of 

 oxidation. 



An apparently necessary condition for the formation of the 

 vanadium-cupferron precipitate seems to be a slight acidity of 

 the solution. Experiments made in this connection showed 

 that if aqueous solutions of sodium vanadate and of cupferron, 

 both made neutral to litmus, were mixed the resulting solution 

 became alkaline (evidently due to ammonia liberated), no pre- 

 cipitate being formed. This alkalinity must be overcome by 

 addition of acid (hydrochloric or sulphuric) and a slight excess 

 must be used in order to bring about complete precipitation. 



The precipitate, transferred to the filter, is washed with a 

 solution containing about ten cubic centimeters of concentrated 

 *Chem. Zeitung, xxxv, 223. 1911. 



