206 Gooch and Gilhert — Ammonium Vanadate. 



which were found to be trifling when care was used, are 

 mechanical and not due to volatilization ; and, secondly, that in 

 his experience the average error of seven trials resulted in a 

 loss of 0*0029 grm. whetlier upon 0-1398 grm. or 0-2796 grra. 

 of V2O5. Holverscheit rejects both the method of v. Hauer 

 and that of Ditto as inexact on account of the solubility of the 

 ammonium metavanadate. 



In 1883,* previous to the proposal of Ditto, Wolcott Gibbs 

 applied in the determination of vanadic acid in the vanadio- 

 molybdates (and sometimes in vanadio tungstates), another and 

 much simpler modification of the method of Berzelius. Gibbs' 

 method consists in boiling the double vanadate with ammonia 

 (to convert the complex salt into a mixture of vanadate and 

 molybdate), adding a saturated solution of ammonium chloride 

 in large excess, concentrating the liquid kept alkaline with 

 ammonia to a small volume, standing twenty-four hours, col- 

 lecting the precipitated ammonium vanadate upon an asbestos 

 Alter in a perforated crucible, washing with a cold saturated 

 solution of ammonium chloride, and, either igniting the pre- 

 cipitate and weighing the residue of Yfi^ upon the asbestos, 

 or dissolving the precipitate with boiling water, reducing to 

 the condition of ^2^4 and titrating by permanganate. This 

 method is called in question by Eosenheim,t who gives analyt- 

 ical results of certain experiments which, according to Rosen- 

 heim's description, are not at all upon the lines laid down by 

 Gibbs. In the first place nothing is said by Rosenheim as to 

 concentrating the mixture to a relatively small volume after 

 adding a saturated solution of ammonium chloride in very large 

 excess ; and in the second place Gibbs did not make the final 

 washing with dilute alcohol, as Rosenheim says he did, but 

 finished the washing with a cold saturated solution of pure 

 ammonium chloride. Rosenheim's variation of the experi- 

 mental procedure in these important particulars, vitiates his 

 conclusions with regard to the precipitation of vanadic acid 

 from solution by ammonium chloride, that "small amounts 

 nevertheless remain, as Roscoe rightly affirms, in solution." 

 Rosenheim's opinions of the method are echoed by Milch, J 

 Liebert§ and Euler.|| 



We have thought it desirable, therefore, to investigate anew 

 the question as to whether the precipitation of ammonium 

 metavanadate by ammonium chloride is complete enough to 

 place that mode of separating vanadic acid from solutions of 

 its salts within the list of good analytical methods. 



The ammonium vanadate used in our experiments was ana- 



* Proc. Am. Acad,, x, 242, 249; Am. Chem. Jour., v, 371, 378. 

 t Inaug. Diss., Berlin, 1888. X Inaug. Diss., Berlin, 1887. 



§ Inaug. Diss., Halle, 1891. || Inaug. Diss., Berlin, 1895. 



