1867.] 



Prof. Roscoe on Vanadium. 



225 



proved to give accurate results with a vanadium oxide of known composi- 

 tion, the point of maximum oxidation being obtained when the solution 

 became pink. According to this method, 100 parts of vanadium pentoxide 

 were shown to have lost 26*53 per cent, of oxygen on reduction with zinc ; 

 the percentage loss from Y2O. to ^ fi^ is 26*3. 



When the neutral lavender-coloured solution of a monoxide salt is allowed 

 to stand exposed to the air for a few seconds, the colour changes to a deep 

 chocolate-brown from absorption of oxjgen ; indeed this reaction for 

 oxygen is as delicate as that of an alkaline pyrogallate. If air be passed 

 through the acid lavender-coloured solution of vanadous sulphate, oxygen 

 is absorbed, and the liquid assumes a permanent blue colour, and the vana- 

 dium is contained in solution as dioxide. If the free acid contained in the 

 lavender solution be neutralized by zinc, the Uquid on exposure to air at- 

 tains a permanent brown tint, which, on addition of acids, becomes green, 

 and the solution contains sesquioxide. 



(2) Vanadium Sesquioxide, \ A (Berzelius's suboxide). — Ob- 

 tained as a black powder by reducing vanadium pentoxide in hydrogen 

 ^ at red heat. When exposed warm to the air it glows, absorbs oxygen, 

 and passes into the highest oxide. At the ordinary atmospheric tem- 

 perature it slowly absorbs oxygen, and is converted into dioxide. Vana- 

 dium sesquioxide is insoluble in acids, but may be obtained in solution by 

 the reducing action of nascent hydrogen evolved from metallic magnesium 

 upon a solution of vanadic acid in sulphuric acid. The changes of colour 

 observed in the case of the monoxide solutions do not continue beyond the 

 green, and the Hquid contains vanadium in solution as sesquioxide. 100 

 parts of vanadium pentoxide were found to lose, on reduction with mag- 

 nesium, 17' 7 per cent, of oxygen ; the loss on reduction to Vs^s ^^'^ 

 per cent. Solutions of vanadium sesquioxide can also be obtained by par- 

 tial oxidation of the lavender-coloured solution containing monoxide. 



Chlorine attacks the sesquioxide in the manner first pointed out by Ber- 

 zelius according to the formula 3 (Y,03)-f-6Cl,= Y,Og-f4(YOCl3). 



(3) Vanadium Dioxide,YO^=83'2 (the vanadic oxide of Berzelius). — This 

 oxide was obtained by Berzelius by precipitation from its salts. It may 

 also be prepared in the form of blue shining crystals by allowing the 

 sesquioxide to absorb oxygen at ordinary temperatures. It is contained 

 in solutions, having a bright blue colour, prepared by the action of mode- 

 rate reducing agents, such as sulphur dioxide and sulphuretted hydrogen, 

 oxalic acid, &c., upon vanadic acid in solution. 100 parts of vanadium 

 pentoxide were found to lose, on reduction with the two first-named agents, 

 9 03 per cent. ; the loss on reduction to YO^ is 8 "75. Solutions containing 

 the dioxide are obtained by passing air through acid solutions of the 

 monoxide until a permanent blue colour is attained. 



(4) Vanadium Pentoxide, Y^O^ (vanadic acid= 182'4). — The properties 

 of this oxide and its compounds are considered only so far as is necessary 

 for the elucidation of the true atomic weight of the metal. 



