418 MM. Svanberg and Struve on the Atomic Weight 



fact, that we have succeeded in preparing the bimolybdate of 

 soda. 



Double salt of the Bimolybdate of Potash and Trimolybdate 

 of Potash. — The formula of the crystallized salt is 4KaO, 

 QMoO 3 + 6HO, or 3KaO, 2Mo O 3 + 3KaO, MoO 3 + 6HO, 

 or 3KaO, MoO 3 + 5KaO, SMoO 3 + 12HO. 



When concentrated nitric or muriatic acid is added with 

 constant agitation to a solution of molybdic acid in carbon- 

 ate of potash, on the addition of each drop a precipitate re- 

 sults, which however soon redissolves. The addition of acid 

 is continued until the precipitate no longer entirely dissolves, 

 and the liquid is slightly opalescent ; it is then set aside, when 

 this salt gradually crystallizes ; but if the solution is very 

 concentrated it is precipitated in a few minutes. The sepa- 

 ration of this salt from concentrated solutions occurs even 

 though the liquid is strongly alkaline. The salt is collected 

 on a filter, not washed with water, but as soon as the mother- 

 ley is drained off dried as quickly as possible between folds 

 of bibulous paper. 



On slow crystallization it separates in six-sided prisms, four 

 faces of which are very predominant, with truncations upon 

 the two narrow faces. When the salt separates rapidly, it 

 appears under the microscope in the form of rhombohedrons, 

 which mutually intercept each other in the centre, and so 

 form minute stars. The salt contains water of crystalliza- 

 tion, which it loses when heated. It melts at a red heat, 

 and solidifies into a crystalline mass on cooling, which dis- 

 solves with difficulty in water. It is soluble in cold water, 

 but is very readily decomposed, so that it can only exist in the 

 perfectly dry state, or in those liquids from which it separated. 

 It is decomposed by water into the trimolybdate of potash 

 and the neutral molybdate of potash. We shall return again 

 to this phenomenon. 



Analysis. — I. 1*5385 grm. salt obtained by precipitating 

 with nitric acid, lost 0*0885 water on ignition, and gave 0*6083 

 sulphate of potash, or 0*328 potash. 



II. 1*1175 grm. salt of the same preparation gave 0*0635 

 water and 0*4422 sulphate of potash = 0*2390 potash. 



III. 0*949 grm. salt of a different preparation with nitric 

 acid gave 0*058 water and 0*3655 sulphate of potash = 0*1975 

 potash. 



IV. The salt for this analysis was obtained by evaporating 

 a solution of molybdic acid in carbonate of potash with a large 

 excess of alkali. A portion of the salt separated from the 

 hot solution, the other portion on cooling, when the entire 

 mass solidified. On treatment with water this salt was left as 



