414? MM. Svanberg and Struve on the Atomic Weight 



We employed in these researches a sulphuret of molyb- 

 denum from Lindas in Smaland, in Sweden, which was very 

 pure, and of which an abundant stock was at our disposal. 

 This mineral, which was mixed with but small portions of 

 gangue, was reduced to a fine powder, and then roasted on 

 a shallow earthenware dish over a charcoal fire, constantly 

 stirring it. From 100 to 200 grammes of the mineral were 

 roasted at a time, and the operation lasted a couple of hours, 

 when so much molybdic acid had formed, that the entire mass, 

 while hot, was throughout yellow and adhered to the dish. 

 When it had cooled the mass was treated in a closed flask 

 with ammonia, which took up all the molybdic acid and left 

 a considerable portion of the mineral and other impurities un- 

 dissolved. These operations had to be repeated several times 

 with the insoluble portion. The solution of the molybdic acid 

 in ammonia was evaporated to a small bulk, and the fol- 

 lowing process adopted to obtain a perfectly pure acid ; the 

 solution contains besides molybdic acid, minute quantities of 

 alumina and oxide of copper, and what is more inconvenient, 

 phosphoric acid. To remove these impurities, the ammoni- 

 acal solution of the molybdic acid is mixed with an excess of 

 carbonate of potash and evaporated ; this separates a portion 

 of the alumina, which is removed by filtration. The clear so- 

 lution is evaporated to dryness and heated to redness in a 

 platinum crucible. The ignited mass is treated with water, by 

 which a solution of molybdate, carbonate with some sulphate 

 and phosphate of potash is obtained, while alumina and oxide 

 of copper remain undissolved. The filtered solution of the 

 potash salts is again evaporated to dryness, the dry mass 

 mixed with twice its weight of sulphur, and the whole heated 

 to redness either in a porcelain crucible or in a glass flask, 

 the mouth of which can be easily closed with a glass stopper. 

 We used a glass flask, placed it in a Hessian crucible, and 

 surrounded it with sand : the temperature is gradually in- 

 creased and continued until no more sulphur burns away, 

 when the entire mass is at a low red heat. After cooling, the 

 whole is treated with hot water, which separates it into a 

 blackish green mass and a red solution. It is filtered as 

 hot as possible, pouring the solution only upon the filter and 

 adding more hot water to the residue. When this water is 

 no longer coloured yellow, a few drops of carbonate of potash 

 are added, and the whole heated with constant agitation until 

 it boils. This treatment with water, carbonate of potash, and 

 filtration, is continued until a little of the filtered liquid, on 

 being mixed with muriatic acid, neither deposits sulphur nor 

 smells of sulphuretted hydrogen. By this means all the phos- 



