208 Gooch and Gilbert — Ammoniiom Vanadate. 





Table I. 





NH4VO3 taken. 



V2O5 present. 



V2O5 found. 



Error. 



grams. 



grams. 



grams. 



grams. 



0-5 



0-3807 



0-3814 



0-0007 + 



0-5 



r< 



0-3818 



0-0011 + 



0-5 



li 



0-3813 



0-0006 + 



0-5 



a 



0-3808 



0-0001 + 



0-5 



u 



0-3808 



0-0001 + 



0-5 



i( 



0-3799 



0-0008 — 



vanadium by volumetric means rather than to go through the 

 tedious and exacting process of ignition to recover the vana- 

 dium pentoxide. Gibbs used the method of reduction by 

 hydrogen sulphide, and titration of the tetroxide by perman- 

 ganate, but for the purpose of testing the method we have 

 thought it best to use the same method for determining the 

 metavanadate separated which was used to determine the com- 

 position of the vanadate taken, viz., Holverscheit's iodometric 

 method. In the beginning some trouble was experienced in 

 the proper handling of the separated vanadate for this purpose. 

 To dissolve the precipitate in hot water introduced too much 

 hot water into the distilling flask ; Altering on paper and then 

 putting paper and vanadate into the flask together introduced 

 an error, due probably to the action of the freed bromine upon 

 the paper. The difficulty was Anally overcome satisfactorily 

 by collecting and washing the separated ammonium metavana- 

 date upon asbestos felt deposited upon a perforated platinum 

 cone of considerable size,* rolling up the felt enclosing the 

 crystals of vanadate, then putting asbestos and vanadium into 

 the distillation flask, without addition of any water, ready for 

 the addition of potassium bromide and hydrochloric acid 

 according to Holverscheit. The use of so much asbestos made 

 it difficult, however, to boil the mixture of acid, bromide, vana- 

 dium and asbestos, so recourse was taken to heating this mix- 

 ture in the hot air chamber of a high temperature paraffin bath. 

 The mass of asbestos made it necessary to use more hydro- 

 chloric acid to overcome the viscosity of the mixture, and the 

 use of so much acid introduced the element of danger that the 

 volatilization of the acid to the receiver containing potassium 

 iodide might, in presence of air, set free iodine outside the 

 reaction of the process ; so the flask was connected with a car- 

 bon dioxide generator, and the operation was carried on in an 

 atmosphere of carbon dioxide. With the exception of the 

 paraffin bath substituted for the burner as a source of heat, the 

 arrangement of the apparatus is shown in the accompanying 

 flgure. Following with 1-5 grams of potassium bromide, the 

 introduction of asbestos and vanadate, the distillation flask B 



* Am. Chem. Jour., vol, i, p. 320. 



