Browning and Palmer — Vanadium as /Silver Vanadate. 221 



Tlie results, recorded in Series A of Table II, indicate that 

 the composition of the precipitate formed in neutral solution 

 approximates closely to the meta-form. 



In the experiments recorded in Series B of Table II, the 

 solution of annnoniuni vanadate was made amuioniacal with 

 ammonium hydroxide, and this solution was made neutral by 

 boiling until the ammonia was completely expelled. To this 

 solution, diluted to about 200""', and heated to boiling, silver 

 nitrate was added, and the procedure given above was followed. 

 The results indicate that the precipitate formed by adding 

 silver nitrate to a solution made neutral by boiling off the 

 ammonia from an ammoniacal solution, is of constant compo- 

 sition. 



The experiments of Series C were made to determine 

 whether any solution containing vanadium could be brought 

 into the condition in which the silver metavanadate would be 

 precipitated on the addition of silver nitrate, by making ammo- 

 niacal and boiling off the ammonia. To this end the solution 

 of ammonium vanadate was made acid with nitric acid, then 

 made ammoniacal with ammonium hydroxide, and boiled to 

 expel the anmionia: the solution was then treated as in the 

 experiments of Series A. This method, as will be seen, gave 

 the most satisfactory results. In this connection it should be 

 noted that the ammoniacal solution, which is yellow at first, 

 becomes colorless during the boiling, until finally, when the 

 ammonia is almost completely expelled, the solution begins to 

 turn yellow ; the boiling should be stopped as soon as the 

 solution begins to turn faintly yellow, because, if the boiling 

 is continued further, the solution becomes too acid, and the 

 precipitate which forms on the addition of silver nitrate has 

 a varying composition which does not correspond to the meta- 

 condition. 



The ease with which the silver vanadate settled out on stir- 

 ring suggested that the vanadium might be estimated volu- 

 metrically with a fair degree of accuracy, by adding a standard 

 solution of silver nitrate to the hot neutral solution containing 

 the vanadium, and noting the point at which the precipitation 

 ceased : but attempts to do this met with unsatisfactory results. 



The gravimetric estimation of silver by the addition of 

 an excess of a solution of ammonium vanadate to the solution 

 containing the silver was also tried, but was abandoned on 

 account of the unsatisfactory character of the precipitate and 

 the difficulty with which it filtered. 



