312 Royal Institution : — Prof. Roscoe on Vanadium, 



colour, ultimately assumes a permanent lavender tint. This solution 

 of V 2 O 2 in sulphuric acid acts as a most powerful reducing agent, 

 bleaching indigo solution and other vegetable colouring-matters as 

 rapidly as chlorine ; it also absorbs oxygen with avidity from the 

 air, forming a deep-brown solution. The other oxides of vanadium 

 may be obtained in solution by the action of various reducing agents 

 on the sulphuric solution of vanadic acid. Thus, by the action of 

 nascent hydrogen evolved from magnesium a permanent green tint is 

 obtained, and the vanadium is contained in solution as the trioxide, 

 V 2 3 ; whilst if moderate reducing agents, such as sulphurous acid, 

 sulphuretted hydrogen, or oxalic acid are employed, the colour of the 

 liquid does not pass beyond the blue stage, and the vanadium is con- 

 tained in solution as tetroxide, V 2 Q 4 *. The different colours of so- 

 lutions containing these oxides was exhibited by means of the mag- 

 nesium light. 



The fact that the lemon- coloured chloride (the terchloride of Ber- 

 zelius) contains oxygen was clearly demonstrated during the dis- 

 course by passing the vapour from a few grammes of the substance, 

 together with perfectly pure hydrogen gas, over red-hot carbon. A 

 portion of the oxygen of the oxychloride unites with the carbon to 

 form carbonic acid, and the presence of this gas was shown by the 

 precipitation of barium carbonate in clear baryta-water contained in 

 two test-tubes placed one before the other. At the commencement of 

 the experiment the carbonic acid was entirely absorbed by the small 

 quantity of baryta-water contained in the first test-tube ; but after 

 some time the hydrochloric acid gas simultaneously produced by the 

 decomposition of the chloride saturated this liquid, expelling the 

 carbonic acid gas, which, being carried forward into the second test- 

 tube, threw down a bulky precipitate of barium carbonate, thus show- 

 ing that the turbidity could not possibly be due to the presence of any 

 vanadium compound. It was found quite unnecessary to place a 

 tube containing heated copper oxide after the red-hot carbon for the 

 purpose of oxidizing any carbonic oxide gas which might be formed, 

 inasmuch as carbonic acid was always left in sufficient quantity 

 to give a considerable precipitate. No methed has been found for 

 separating the whole of the oxygen from the oxychloride ; and hence 

 it has been impossible to make the above experiment quantitatively. 

 Solid oxychlorides are obtained by the action of hydrogen upon the 

 oxy trichloride, one of which resembles mosaic gold, possessing a 

 bright metallic bronze-like lustre, and having been taken for the metal 

 by Schafarik. 



* In his communication to the Royal Society (Bakerian Lecture, Pro- 

 ceedings of the Royal Society, vol. xvi. p. 220), the author gave the empi- 

 rical formula VO and VO 2 to the first and third oxides of vanadium, as 

 the molecular weights of these oxides have not been determined, and it is 

 uncertain whether they obey the law of even atomicities, or, like the only 

 corresponding compounds, the nitrogen oxides, are exceptions to this law. 



On consideration, the author has, however, thought it best to adopt the 

 double formula, as urged by Sir Benjamin Brodie on the occasion above 

 referred to. 



