272 PROCEEDINGS OP THE AMERICAN ACADEMY. 



preparing the potassium salt a large excess of potassic bromide should 

 be used : the bromide in this, as in many other cases, appears to be 

 preferable to the chloride and nitrate. In these salts the molybdic 

 dioxide may be easily and accurately determined by titration with 

 permanganate, after adding sulphuric acid. The solutions of the mo- 

 lybdico-tungstates readily absorb oxygen from the air, forming molybdic 

 teroxide, a fact which must be taken into account in analysis. 



Molybdic hydrate, Mo(OH)4, quickly reduces M0O3 "^ ^ solution 

 of 14:6 ammonium salt, and gives a fine blue liquid, which probably 

 contains M02O5 or M0O2 + M0O3. When a very cold solution of 

 ammouic molybdate is employed, and molybdic hydrate is added in 

 small portions at a time, the solution becomes yellow, then quickly 

 green, and finally blue. It is possible that a molybdico-molybdate, 

 OTM0O2 . nMoOg . joRoO, is formed at first. Molybdic hydrate reduces 

 both molybdic and tungstic teroxides in phospho-molybdates and 

 phosplio-tungstates. Analyses of the potassium, calcium, and barium 

 molybdico-tungstates were made with salts which perhaps were not 

 absolutely pure. Tiie formulas obtained appeared to be respectively 

 12 WO3 , M0O2 • 5 KoO + 16 aq. ; 12 WO3 . M0O2 . 5 CaO + 32 aq. ; 

 and 12 WO.j . M0O2 . 6 BaO + 30 aq. ; but these are given with much 

 reserve. In these the molybdenum was determined by titration with 

 permanganate, and the sum of the molybdic and tungstic teroxides, 

 after oxidation, by precipitation of the neutral solution with calcic 

 or baric chloride. Tungstic teroxide could then be determined by 

 difFierence. 



It seems at least probable that tungstico-molybdates corresponding 

 to molybdico-tungstates, as, for example, 1 2 M0O3 . AVO2 . x RO, also 

 exist. 



Uranoso- Tungstntes. 



When uranic oxide is dissolved in dilute sulphuric acid, and the 

 solution is treated with metallic zinc, a solution of sulphate of uranic 

 dioxide is formed which after a time deposits a gray-green powder 

 insoluble in cold water, and probably a basic sulphate. This body 

 treated with a solution of 12:5 sodic tungstate gives at once an olive- 

 green crystalline salt very insoluble in hot water. The supernatant 

 liquid has a peculiar reddish tint. The dark olive-green salt is 

 oxidized by boiling with nitric acid and gives a yellowish white mix- 

 ture, or possibly compound, of uranic and tungstic teroxides, easily 

 decomposed by boiling with caustic alkalies, with separation of uranic 

 oxide and formation of sodic tungstate. A solution of 12:5 potassic 



