Gooch and Gilbert — Ammonium Vanadate. 207 



lyzed by the iodometric method of Holverscheit,^ and found to 

 contain 76*14: per cent of Yfi^ 



The ammonium chloride employed was shown to be pure 

 and free from iron by heating a solution of it to boiling, adding 

 bromine water and a slight excess of ammonia, and filtering. 

 No residue whatever remained upon the filter. 



In each experiment a weighed portion of ammonium vana- 

 date was put in a small beaker and heated with about 25^° of 

 water and a few drops of ammonia upon the steam bath until 

 solution was complete. To the solution were added 25^*= of a 

 cold saturated solution of ammonium chloride and a few drops 

 of ammonia. The mixture remained upon the steam bath, 

 with addition from time to time of a little ammonia to keep 

 the metavanadate of normal composition and colorless, until 

 the volume had been reduced to about 25^^, and was then cooled. 

 On cooling, a small amount of ammonium chloride crystallized 

 out, but only a little if the proportion had been properly 

 adjusted. It too large an amount of ammonium chloride 

 crystallized out, it was nearly redissolved by the cautious addi- 

 tion of ammonium hydroxide. The mixture was allowed to 

 stand twenty-four hours to insure complete crystallization of 

 the ammonium metavanadate, and was then filtered on a weighed 

 asbestos filter and perforated crucible, the precipitate being 

 transferred and washed with a cold saturated solution of 

 ammonium chloride. Crucible and precipitate were heated, at 

 first very gently to drive off the ammonium chloride without 

 occasioning mechanical loss of the vanadium, and finally to 

 redness and fusion of the pentoxide remaining. At the outset 

 some difticulty was occasionally found in removing from the 

 walls of the beaker the adherent crystals of ammonium vana- 

 date, but this difiiculty was overcome, in the experiments 

 recorded, by the device of forming upon the walls of the 

 beaker before using it a film of parafiin of extreme thinness by 

 rinsing the beaker with a dilute solution of parafiin in naphtha 

 (0"5 gram, of parafiin in SOO^'^ of naphtha) and allowing the 

 naphtha to evaporate. Crystals of the vanadate adhering to 

 the walls of the beaker thus previously prepared, are easily 

 removed by means of the ordinary rubber or " policeman." 

 Table I contains the record of six consecutive experiments 

 made after some preliminary study of the method. The 

 washings and filtrate were in several instances acidified with 

 hydrochloric acid and tested with hydrogen dioxide without 

 giving indication of the presence of vanadium. 



These results are sufficient to show that the method of Gibbs 

 is capable of yielding an analytical separation of value, but as 

 Gibbs pointed out it is ordinarily preferable to estimate the 



* Inaug. Diss., Berlin, 1890, p. 49. 



