of Molybdenum and some of its Compounds. 42 1 



and of the anhydrous salt — 



I. IV. V. Mean. 



Potash . . 18*840 18-183 18*614 18*546 



Molybdic acid 81-160 81*817 81-386 81*454 



The composition of the air-dried salt, according to theory, 

 is — 



a. Calculated. b. Calculated. 



1 at. Potash . . . 588-856 16'388 588-856 16'570 

 3 at. Molybdic acid 2666-898 74'221 2627-487 73-935 

 3 at. Water . . . 337-437 9-391 337-437 9-495 

 8593-191 100-000 3553*780 100-000 

 and of the anhydrous salt — 



1 at. Potash . . . 588*856 18'087 588*856 18*308 

 3 at. Molybdic acid 2666-898 81*913 2627*487 81-692 



3255*754 100*000 3216*343 100*000 



As above stated, this salt is obtained by the decomposition 

 of the previously-described double salt; and as the trimolyb- 

 date separates in an almost insoluble state, we made the fol- 

 lowing quantitative experiment. 



5*7178 grms. of the crystalline double salt were dissolved 

 in cold water and set aside in a covered vessel ; after two days 

 the first flakes began to separate, and the decomposition pro- 

 ceeded slowly. After twelve days the trimolybdate of potash 

 which had separated was collected upon a weighed filter, and 

 after being dried in the air, weighed 4*6087 grms. The fil- 

 tered liquid was evaporated in the water-bath to dryness ; on 

 re-solution in a little water it left 0*0053 grm. trimolybdate. 

 The filtered liquid was neutral, but absorbed carbonic acid 

 from the air, acquired an alkaline reaction, and gradually 

 deposited still more trimolybdate. 



100 parts of the crystalline double salt give, according to 

 this experiment, 80*695 parts trimolybdate of potash ; the de- 

 composition then takes place according to the following for- 

 mula: — 



2 at. (4KaO, 9Mo0 3 + 6HO)\ f5(KaO, 3Mo0 3 + 3HO) 



are decomposed into . .J \3(KaO, Mo0 3 + xHO) 



According to this formula 100 parts of the double salt 

 should yield 81*438 parts trimolybdate, and this result agrees 

 as accurately as could be expected with the experiment. 



When trimolybdate of potash is exposed, to a current of 

 hydrogen, there is no reaction until the salt is fused ; reduc- 

 tion then occurs, water is formed, and the fused mass gra- 

 dually becomes solid, acquiring a shining brown colour. 



0*5525 grm. fused and pulverized trimolybdate of potash 



