of Molybdenum and some of its Compounds. 417 



with those calculated, that we have in each case obtained an 

 excess of potash. We nevertheless believe that this salt is 

 the neutral molybdate of potash, but the reason why no per- 

 fectly pure product can be obtained is the mode of prepara- 

 tion of this salt from a very alkaline liquid. 



In these analyses, and in all the subsequent ones, the potash 

 was determined according to the following method : — After 

 the salt had been heated to redness in a platinum crucible to 

 determine the amount of water of crystallization, it was dis- 

 solved in water ; but if the salt after ignition was insoluble or 

 sparingly soluble in water, we added to it a few drops of ammo- 

 nia. The solution was then mixed with an excess of hydro- 

 sulphate of ammonia and afterwards with muriatic acid,. which 

 instantly precipitates tersulphuret of molybdenum, which, ac- 

 cording to the concentration of the liquid, had sometimes a 

 brown, and at other times a black colour. If care had not 

 been taken to add a sufficient quantity of hydrosulphate of 

 ammonia at the commencement, and the whole of the mo- 

 lybdenum has not been precipitated (which is indicated by 

 the colour of the solution), this fault can only be made 

 good by redissolving the whole in ammonia and hydrosul- 

 phate of ammonia, and again precipitating it. The precipi- 

 tated sulphuret of molybdenum, which very quickly subsides, 

 is collected upon a filter and washed with water containing 

 sulphuretted hydrogen and muriatic acid. The filtrate is then 

 evaporated in a counterpoised platinum crucible, the excess 

 of chloride of ammonium driven off at a gentle heat, the resi- 

 due dissolved in water and sulphuric acid, again evaporated, 

 and the potash determined with the usual precautions as neu- 

 tral sulphate of potash. In most of the analyses an excess of 

 potash will be found, which is owing to the readiness with 

 which the sulphuret of molybdenum becomes oxidized. 



Bimolybdate of Potash. — We did not succeed in preparing 

 this salt, for on fusing together a weighed quantity of trimo- 

 lybdate of potash with the requisite quantity of carbonate of 

 potash to produce the bimolybdate, we obtained after ignition, 

 the carbonic acid being expelled with effervescence, a white 

 mass which solidified in a crystalline state on cooling, and on 

 pouring water over the fused mass a small quantity dissolved 

 at first, but in a few minutes the liquid grew turbid, and the 

 whole salt was gradually decomposed into the neutral and the 

 tribasic molybdate of potash. We do not mean however, by 

 this experiment, to deny the existence of this salt, for it is 

 highly probable that it will be more stable when produced in 

 liquids of a certain degree of concentration, or in which other 

 salts are contained. This view is moreover confirmed by the 



