OF ARTS AND SCIENCES. 271 



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able with our present methods. Baric oxide in these salts is best esti- 

 mated by difference, as the direct estinaation almost always gives too 

 high a percentage. 



60 : 3 : 1 : 1 Barium Salt. — When ammonic vanadate is heated 

 in a porcelain crucible until all the ammonia is expelled, the 

 greenish residue consists, as already stated, chiefly of a mixture of 

 vanadic dioxide and pentoxide. If this mixture be added in small 

 portions at a time to a boiling solution of the baric phospho-tungstate, 

 20 WO3 . P2O5 . 6 BaO, already described, the liquid takes at once a 

 rather dull green color. The filtrate from the excess of mixed 

 oxides, after evaporation in a water-bath and standing for some hours, 

 yields a mass of deep green crystals, mechanically mixed with a rela- 

 tively small proportion of a fine white powder, which may easily be 

 removed by washing with cold water and pouring off the powder in 

 suspension. The dark green crystals are regular octahedrons, fre- 

 quently in long aggregates and beautifully defined. The salt is rather 

 insoluble in cold but readily soluble in hot water, with a dark and 

 rather dull green color. The cold solution, after adding dilute sul- 

 phuric acid, is not sensibly oxidized by potassic hypermanganate or in 

 alkaline solution by iodine. The hot solution is oxidized by bromine 

 and by nitric acid, and becomes deep orange-red. At a boiling heat 

 potassic hj'permanganate also oxidizes it, the quantity required for 

 oxidation being very small, so that it can with difficulty be estimated. 

 Of this salt, — 



1.2596 gr. gave 0.9178 gr. mixed oxides = 72.86% 



1.0160 gr. lost on ignition 0.1362 gr. = 13.40% 



1.4649 gr. " " 0.1969 gr. =13.44% 



1.8580 gr. gave 0.0624 gr. P^O.Mg^ = 2.15% Pp^ 



1.3846 gr. " 0.0105 gr. V265 = 0.76% 



1.1972 gr. « 0.0131 gr. " = 1.09% 



Tn these analyses the vanadic pentoxide was determined directly in 

 the salt, by boiling with chlorhydric acid and titrating. In two other 

 analyses, the vanadic dioxide was first completely oxidized by means 

 of bromine ; the whole quantity of vanadium was then determined as 

 before. The percentage of vanadic dioxide was then calculated from 

 the excess of V^O^ over that found by direct analysis. In this 

 process, — 



1.1379 gr. gave 0.0161 gr. V^O^ = 1-44% 



1.1714 gr. « 0.0200 gr. " =1.71% 



