276 AGRICULTURAL ANALYSIS 



and filter. Add to the filtrate ammonium chlorid in excess 

 about 3.5 grams for each 10 cubic centimeters of the solution, 

 and allow to stand, with occasional stirring, for some time. Am- 

 monium vanadate, insoluble in a saturated solution of ammonium 

 chlorid, separates as a white powder. It is necessary to keep the 

 solution alkaline, and a drop of ammonia should be added from 

 time to time for this purpose. The appearance of a yellowish 

 tint at any time indicates that the solution has become acid, and 

 this acidity must be corrected, or else the results will be too low. 

 Separate the ammonium vanadate by filtration ; wash first with 

 a saturated solution of ammonium chlorid containing a little free 

 ammonia, and then with alcohol. Dry, ignite, and moisten with a 

 few drops of nitric acid ; again ignite to obtain the compound as 

 vanadium pentoxid, V 2 O 5 . This compound contains 56.22 per 

 cent, of vanadium. 



The method of Rosenheim and Holverscheit may also be used. 37 

 It is based on the preliminary precipitation of the vanadic acid as 

 a barium or lead salt. The substance supposed to contain vana- 

 dium is first brought into solution in such a manner as to secure 

 it as vanadic acid, which is then precipitated with barium chloric! 

 or lead acetate. The precipitate is boiled with hydrochloric acid 

 and potassium bromid, and the liberated bromin determined by the 

 quantity of iodin set free from potassium iodid. In the absence of 

 bodies, such as molybdic acid, which are reduced by sulfurous 

 acid or hydrogen sulfid the vanadic acid may also be determined 

 by reducing it with one of these reagents and, after removing the 

 excess by boiling, titrating the vanadium tetroxid with potas- 

 sium permanganate. When vanadic and phosphoric acids occur 

 together the former may be first reduced to tetroxid with sulfurous 

 acid, and after expelling excess of this reagent, the phosphoric 

 acid may be separated with molybdate solution and removed by 

 filtration. When the amount of vanadic acid is large the phos- 

 phoric acid should be separated rapidly at 55-6o, using a con- 

 siderable excess of the molybdate ; or the vanadic acid may first be 

 determined in the solution volumetrically by the bromin pro- 



87 Ueber Vanadinwolfratnsame, Dissertation, Berlin, 1888. 



Ueber die quantitative Bestimmung des Vanadins. Dissertation, Ber- 

 lin, 1890. 



