1867.] 



Prof. Koscoe on Vanadium. 



223 



II. Occurrence and Vreparation of the Vanadium Compounds, 



The sources of vanadium have hitherto yielded the compounds of this 

 metal in extremely small quantities, and consequently our knowledge of the 

 substance is but limited. The attention of the author was drawn to the 

 occurrence of vanadium in some of the copper-bearing beds of the Lower 

 Keuper Sandstone of the Trias, worked at Alderley Edge and Mottram St. 

 Andrews, in Cheshire. He obtained a large quantity of a lime precipitate, 

 containing nearly 2 per cent, of vanadium, obtained in working up a poor 

 cobalt-ore from Mottram in a mine now closed. The precipitate, contain- 

 ing mainly arsenic, iron, lead, copper, vanadium, and lime, v/ith sulphuric 

 and phosphoric acids, was first well furnaced with ground coal, to drive off 

 the greater portion of the arsenic, and then roasted with one-quarter of its 

 weight of soda-ash, so as to convert the vanadium into a soluble vanadate, 

 and on lixiviation arsenic and the heavy metals were completely thrown 

 down by sulphuretted hydrogen. The deep-blue solution was neutralized 

 by ammonia, the precipitated vanadium oxide dried and oxidized by nitric 

 acid, and the crude vanadium pentoxide thus obtained boiled out with a satu- 

 rated solution of ammonium carbonate. The slightly soluble ammonium vana- 

 date was washed and recrystaUized. In order to prepare pure vanadium pent- 

 oxide from this salt it was roasted, and the powder thus obtained suspended 

 in water into which ammonia gas was passed. The dissolved ammonium 

 vanadate was separated by filtration from a residue containing silica, phos- 

 phates, &c. The pentoxide obtained by heating this salt was free from 

 phosphorus. A second method of preparing the pure vanadium pentoxide 

 consists in decomposing the pure oxy chloride in water, and freeing the pent- 

 oxide from any traces of silica by exposure to hydrofluoric-acid gas. Great 

 difficulty was experienced in obtaining vanadium free from phosphorus ; all 

 the native vanadates contain large quantities of phosphorus. The action of 

 traces of this substance upon vanadium pentoxide is remarkable ; 1 per 

 cent, of phosphoric acid renders crystalline vanadium pentoxide black and 

 amorphous, whilst the presence of the merest trace altogether prevents the 

 reduction of the pentoxide in hydrogen. 



III. Atomic Weight determination of Vanadium by reduction of Vanadium 

 Pentoxide in Hydrogen. 



This method was the one originally employed by Berzelius. It is per- 

 fectly reliable, and yields accurate results when carried out with care and 

 due regard to the necessary precautions, which are detailed in the me- 

 moir. 



In drying the pure hydrogen gas only sulphuric acid can be used, as 

 phosphorus pentoxide used in the last drying-tube was found invariably to 

 be carried over into the boat containing the substance ; and the presence of 

 a trace of phosphoric acid renders the complete reduction to sesquioxide 

 impossible. 



