526 MM. Svanberg and Struve on the Atomic Weight 



in weak and in strong alcohol, with a yellow colonr. But if the 

 dry mass is heated for some time, it gradually assumes a dark 

 yellow colour, but still continues soluble in water. On treating 

 molybdic acid with a little phosphoric acid, a portion separated 

 as a yellow insoluble powder ; more of this is formed every 

 time the solution is evaporated, whether the evaporation be 

 carried on in the water-bath or on the sand-bath. If the dry 

 mass be heated somewhat more strongly in a platinum crucible, 

 it turns green, and on increasing the temperature, fuses to a 

 liquid which solidifies on cooling into a vitreous dark blue or 

 dark green mass. If the temperature be raised so high that 

 the crucible is incandescent, some molybdic acid is volatilized. 

 This coloured mass dissolves with difficulty in cold water ; 

 with boiling water it forms a coloured solution, which, when 

 evaporated with access of air, first becomes colourless and 

 then reacquires the yellow colour. This colour may be in- 

 stantly produced by the addition of a few drops of nitric acid. 



This more or less yellow compound of phosphoric and mo- 

 lybdic acid dissolves readily in ammonia, forming a colourless 

 liquid. But if to the concentrated solution either sulphuric, 

 muriatic, or nitric acid is added (the last is best), a lemon- 

 coloured precipitate is formed as soon as the liquid has an 

 acid reaction. In this case, therefore, none of the phaeno- 

 mena previously described as occurring in the treatment 

 of pure molybdic acid and ammonia take place; there acid 

 salts, partly crystalline, partly amorphous, separated with a 

 white colour whatever acid was used, whilst here, however 

 great an excess of acid is employed, the yellow precipitate 

 only is obtained. Moreover all the compounds of molybdic 

 acid with the alkalies are very readily soluble in an excess of 

 muriatic acid, whilst this yellow precipitate is insoluble. 



When this yellow precipitate is collected upon a filter, the 

 mother-liquor passes through with a yellow colour, and fur- 

 nishes on evaporation more of the yellow salt, so that at last 

 the liquid becomes perfectly colourless. On washing with pure 

 water, the precipitate goes through the filter, which may how- 

 ever be prevented by the addition of a few drops of nitric acid. 

 The colourless mother -liquor, which contains a iarge excess 

 of nitric acid, furnishes on evaporation a colourless vitreous 

 mass, from which ammonia and nitric acid precipitate no more 

 yellow salt; but this residue nevertheless contains molybdic 

 and phosphoric acid, and is acted upon by heat in the same 

 manner as the yellow salt; however, the amount of the preci- 

 pitate is far greater; but further experiments must show how 

 this different behaviour is to be explained. Perhaps the state 

 of the phosphoric acid in these compounds acts a very import- 



