of Molybdenum and some of its Compounds. 419 



a white crystalline powder very sparingly soluble in water ; it 

 was dried in the air; 1-0973 grm. afforded O'O^OS water and 

 0-4474 sulphate of potash = 0*2418 potash. We have also 

 given the per-centage composition of this salt; we leave it 

 however to other chemists to decide in how far this salt is 

 distinct from the others, especially in respect to the amount 

 of water. It appears to contain only 3 atoms of water. 



The per-centage composition of the crystallized salt is, ac- 

 cording to analysis, — 



and of the anhydrous salt — 



4 at. Potash. . . 2355'424 22-744 2355*424 23*007 



9 at. Molybdic acid 8000-694 77'256 7882*461 76*993 



10356*118 100*000 10237*885 100-000 



Trimolybdate of Potash. — Formula of the salt dried in the 

 air KaO, 3MoG 3 + 3HO. This salt can be very readily pre- 

 pared in large quantities and in the purest state. Indeed, 

 the combinations of molybdic acid with potash exhibit a great 

 tendency to pass into this salt. It is prepared by adding 

 water to the preceding double salt, and stirring frequently ; 

 complete decomposition then takes place, and the trimolyb- 

 date separates, being very sparingly soluble in water. This 

 decomposition requires some days, but it is only requisite to 

 warm the liquid to hasten it. When large quantities of the 

 double salt are used, the liquid thickens to such an extent on 

 the separation of the trimolybdate of potash, that the whole 

 becomes a thick paste. When the precipitate no longer in- 

 creases, the entire mass is thrown upon a filter and washed 

 carefully with water. The pure salt is best dried at first 

 in the air and then at a gentle heat, for if exposed while moist 

 to a temperature of 212° a portion dissolves in hot water. The 



