of Molybdenum and some of its Compounds. 423 



stalline and amorphous substances can be distinguished, as 

 was stated when treating of the trimolybdate of potash. All 

 the crystalline salts may be extracted with hot water, which 

 leaves an amorphous residue, that may sometimes be collected 

 on a filter and washed, but at other times it passes through 

 the pores of the filter. It is likewise a chemical combination of 

 molybdic acid with potash. It appears however that a tetra- 

 molybdate or pentamolybdate of potash is precipitated ac- 

 cording to the quantity of nitric acid. It is not a mixture of 

 molybdic acid with some molybdic acid containing potash, for 

 when heated in a platinum crucible it fuses, but not a trace of 

 molybdic acid is volatilized even with the strongest heat. We 

 have analysed two such precipitates. 



Tetramolybdate of Potash, KaO, 4MoO, forms a white cry- 

 stalline powder, which is anhydrous, insoluble in water, readily 

 fusible, and crystallizes on cooling. 



Analysis. — 1*612 grm. salt gave 0*4162 sulphate of potash 

 = 0-2249 potash. 



On comparing the numbers found with those resulting from 

 theory, we have — 



1 at. Potash 588-856 



4 at. Molybdic acid . . . 3555-864 



4144-720 100000 4092*172 100*00 100-000 



Pentamolybdate of Potash, KaO, 5MoO a , also forms a white 

 powder, but of a much finer grain, and very readily passes 

 through the filter. It is anhydrous, fuses and solidifies into a 

 crystalline mass on cooling. 



Analysis. — 2*1815 grms. fused salt gave 0*5033 sulphate of 

 potash = 0*274 potash. 



Theory and analysis give the following per-centage com- 

 position : — 



a. Calc. b. Calc. Found. 



1 at. Potash 588-856 11-698 588-856 11*853 12*468 



5 at. Molybdic acid ...4444830 88-302 4379145 88-147 87*532 



5033-686 100000 4968001 100-000 100000 



The series of combinations of potash and molybdic acid 

 is certainly not closed with the salts here described. In 

 the course of this investigation we have observed several 

 other salts differing in their crystalline form, but did not 

 pursue the subject further, as it was beyond the object of this 

 paper; we will however mention three other salts, in order 

 that should any person take up the examination of the potash 

 salts he may direct his especial attention to these. One salt 

 crystallizes in small six-sided prisms, which when stirred 



