528 MM. Svanberg and Struve on the Atomic Weight 



This salt, which is insoluble in water and acids, appears 

 amorphous even under a high magnifying power, and to con- 

 sist of minute spheres. When treated with potash, ammonia 

 is expelled and a colourless solution obtained. When this 

 salt is heated for some time in a closed platinum crucible, at a 

 temperature below red heat, the whole of the ammonia and 

 water escape, and a confused mass remains, which is partly of 

 a brown, partly of a green colour. On treating this residue 

 with concentrated nitric acid, very little reaction occurs at the 

 ordinary temperature, but on heating it, nitrous acid is given 

 off; the reaction, however, lasts only for a few moments ; the 

 liquid has now a beautiful yellow colour, and the sediment, 

 a grayish-blue powder, is not further acted upon by nitric 

 acid. The insoluble residue behaves like molybdic acid, dis- 

 solves in potash and in ammonia, and upon the addition of an 

 acid, again furnishes the yellow salt. But the yellow solution 

 possesses totally different properties. If this solution is dilute 

 it loses the yellow colour in the cold and becomes colourless, 

 but when heated it again makes its appearance. If this solution, 

 which contains a large excess of nitric acid, is evaporated, 

 some crystals separate on cooling, which appear under the 

 microscope to be minute rhombohedrons. But this compound 

 is not very stable, the mass absorbs water, all the crystals 

 dissolve, and now another compound separates in regular oc- 

 tahedrons. Both these salts are very readily soluble, owing 

 to which we were unfortunately unable to obtain a sufficient 

 quantity of a pure salt for analysis. 



If this yellow liquid be further evaporated, the yellow cry- 

 stalline salt gradually passes into the amorphous yellow com- 

 pound above described. If the yellow ammonia salt is heated 

 with an excess of potash until the liquid no longer smells of 

 ammonia and is partly evaporated, a colourless solution is 

 obtained. On adding nitric acid to it, a yellow crystalline 

 precipitate falls, which is insoluble in an excess of acid; it is 

 collected and washed in the same manner as the preceding 

 ammonia salt. It crystallizes in minute four-sided prisms, is 

 insoluble in water, parts with water at a red heat, melts and 

 solidifies into a crystalline yellow mass on cooling. 



Analysis. — 1*472 grm. salt lost on ignition 0072 water, 

 and gave 306 sulphate of potash = 01 654 potash. But the 

 sulphate of potash contained traces of phosphate of potash. 

 The per-centage composition of the salt dried at 212° is 

 accordingly — 



Potash . . . 11-234 



Molybdic acid 83-875 



Water . . . 4-891 



