186 P, E, Browning — Reduction of Yanadic Acid. 



to the residue after the reduction with hydrobromic and hydri- 

 odic acids led to the series of experiments which it is the pur- 

 pose of this paper to describe. The advantages of the treat- 

 ment of the residue are obvious and the general method has 

 been applied in a number of methods previously developed in 

 this laboratory. In the first place the complicated apparatus 

 necessary for the distillation and collection of the bromine or 

 iodine is unnecessary, an ordinary boiling flask or Erlenmeyer 

 beaker being sufficient. In case the distillation process is pre- 

 ferred, the residue may be treated by the method to be described 

 as a control and the results by both processes allowed to check 

 one another. 



For the work to be described solutions of ammonium vana- 

 date were made and standardized by evaporating measured and 

 weighed portions in a platinum crucible to dryness, and ignit- 

 ing in the presence of a drop of nitric acid. 



The reduction with hydriodic acid was first tried ; the method 

 in general was as follows : Measured and weighed portions of 

 the vanadate solution were placed in the Erlenmeyer beakers, the 

 amounts of potassium iodide indicated in the tables added from 

 a ten per cent solution and finally 10^"^^ of a mixture of sulphuric 

 acid and water in equal parts. The contents of the flask was 

 then boiled until the fumes of iodine were no longer visible 

 and the escaping steam gave no indication of free iodine with 

 red litmus paper.* This point was reached when the volume 

 of the liquid reached about 35'^'''^ If large amounts of potas- 

 sium iodide w^re used the resulting color was green, owing to 

 the presence of iodine, dissolved in hydriodic acid, with the blue 

 tetroxide of vanadium ; if smaller amounts of the iodide were 

 used the resulting color was blue. The flasks were then re- 

 moved from the flame and the contents nearly neutralized by the 

 addition of a solution of potassium of sodium hydroxide,f cooled, 

 and the neutralization completed with potassium bicarbonate 

 in excess ; care being taken to add a few drops of a tartaric 

 acid solution to prevent the precipitation of the tetroxide. To 

 the cooled solution a solution of iodine in potassium iodide was 

 added in slight excess. This point can be quite easily deter- 

 mined, as the iodine is bleached rapidly if the solution is allowed 

 to mix thoroughly as it is drawn from the burette into the 

 flask. After the addition of a distinct excess of the iodine the 

 flask should be closed with a cork coated with paraffin and 

 allowed to stand about one-half hour. It will be noticed that 



* Gooch and Mar, this Journal, xxxix, p. 300. 



f The potassium or sodium hydroxide for this work must be free from alcohol, 

 as the solution is allowed to stand with iodine after neutralization. It was prepared 

 by mixing potassium or sodium carbonate in proper proportions with calcium 

 oxide and filtering off the calcium carbonate. 



