22 
PROEESSOR ROSCOE’S EESEAECHES ON VANADIUM. 
presence of nitric acid and silver solution added, no trace of vanadium goes down with 
the silver. 
Pure silver was prepared with all the precautions detailed by Stas* in his first me- 
moir, and the analyses were conducted in the manner described by him j\ The nitric 
acid was prepared by distilling a large quantity of pure acid until three-fifths had come 
over ; the remainder was then distilled and collected, and on careful testing with silver 
showed not the slightest indication of chlorine. The distilled water used had been care- 
fully redistilled, and likewise gave no indication of chlorine. The weight of silver to be 
taken was calculated from a careful gravimetric analysis, and several volumetric deter- 
minations were made at one time. The weighed quantity of silver was placed with ten 
times its weight of pure nitric acid, sp. gr. 1*2, in well-stoppered 300 cubic centimetre 
bottles, and heated to about 40° C. until all the silver had dissolved. After cooling, the 
bulb containing the weighed quantity of vanadyl trichloride was brought into the bottle, 
the bottle closed, and the bulb broken by shaking ; distilled water was then added, so 
that the weight of the whole liquid amounted to from forty to fifty times that of the 
silver employed. The lower oxides of nitrogen present in solution in the acid reduced 
the vanadium to a bright blue solution, in which the slightest turbidity of silver chlo- 
ride could be well seen. 
In the volumetric determination of chlorine it has already been noticed, both by Gay- 
Lussac and Stas, that when one or two milligrammes of silver per litre still remain in 
solution, a turbidity is produced by the addition of both silver and chloride solution. 
This fact was also observed in the volumetric analyses of vanadyl trichloride; and in 
order to render the results comparable, the course proposed by Stas was invariably 
adopted, viz. that of adding the decimal chloride solution until all turbidity ceased. 
The error thus introduced is, however, extremely small (less than 0-0005), and is coun- 
terbalanced by the error arising from a trace of impurity contained in the silver. 
In several cases the vanadium in the filtrate was estimated by precipitating the excess 
of silver, expelling the acid by evaporation, again filtering from the trace of silver 
chloride which separates out, and evaporating the filtrate to dryness in porcelain, trans- 
ferring to platinum, oxidizing by nitric acid, and weighing the fused acid. 
The following Table contains the results of nine chlorine determinations made 
according to the above method with trichlorides of various preparations. Nos. 1, 2, 3, 
and 4 were made with substances of one preparation, Nos. 5 and 6 of a second prepa- 
ration, Nos. 7 and 8 of a third preparation. 
* Recherches stir les Rapports reciproques des Poids atomiques. Bruxelles, 1860, p. 25.“ 
t Idem, p. 62. 
