20 PHILOSOPHICAL TRANSACTIONS. [ANNO 1706. 



black blistered matter. I then examined the sulphureous acid and sulphate of am- 

 monia which had risen, but did not find any trace of molybdaena. 



I next poured nitric acid diluted with an equal weight of distilled water on the 

 black residuum in the retort, and distilled it. As soon as the acid began to be 

 warm, nitrous fumes were discharged, and when the distillation had been repeated 

 with a 2d portion of nitric acid, I found the whole of the black matter converted 

 into a pale citron-coloured substance, which was the molybdic acid. 



$11. Analysis of the molybdate of lead. — I put 250 grs. of the purified ore re- 

 duced to a fine powder into a glass matrass, and having poured on it 1 oz. of con- 

 centrated sulphuric acid, I digested it in a strong heat during an hour. When the 

 solution was become cool and had settled, the acid was cautiously decanted from 

 the powder, and distilled water was poured on till it came away tasteless. The 

 same operation was repeated twice, so that 3 oz. of sulphuric acid were used. The 

 acid solutions and washings were then filtrated, and were received in a large glass 

 vessel. 



I diluted the pale blue liquor with distilled water, in the proportion of l6 to 1, 

 and afterwards gradually added ammonia till it was completely saturated. The 

 liquor then became deep blue, and appeared turbid. When it had stood about 24 

 hours, a loose pale ochry precipitate subsided, and was collected on a filter, the 

 weight of which had been noted*. This precipitate was edulcorated, and after- 

 wards dried with the filter on the flat top of a tin vessel heated by boiling water, 

 after which the weight of the precipitate was 4.2 grs. The colour of the dry pre- 

 cipitate was yellowish brown, and when dissolved in muriatic acid it was precipitated 

 by prussiate of pot-ash in the state of Prussian blue. 



I now poured part of the clear blue solution, which was composed of sulphuric 

 and molybdic acid saturated with ammonia, into a glass retort, and when about 

 half was evaporated, I continued to add the remainder of the liquor at different 

 times till the whole was become a concrete salt. I then raised the fire and continued 

 the distillation till all the sulphate of ammonia was decomposed or driven over: 

 but as some of the sublimed salt was fixed in the neck of the retort, I turned the 

 bottom of it upwards, and poured some distilled water into the neck, so as to wash 

 out the salt; after this I increased the fire till the whole body of the retort was be- 

 come red-hot -f-. The residuum in the retort was a black blistered mass, on which 

 I poured 3 oz. of nitric acid diluted with an equal portion of water, and having dis- 

 tilled it, I repeated the operation, and thus converted the whole of the black 



* This is one of the many instances which prove the weak affinity between molybdaena and oxygen ; 

 for it is well known that pure ammonia precipitates iron from sulphuric acid, in a state nearly similar to 

 martial aethiops ; but in the present case the iron takes a considerable portion of oxygen from die 

 molybdic acid at the moment that the acid menstruum is saturated by the ammonia, and it is therefore 

 precipitated in the form of a yellowish-brown oxyde, while the molybdic acid being thus deprived of so 

 large a quantity of oxygen, is converted into a blue oxyde which remains in solution. — Orig. 



+ To be certain that all of the ammoniacal salt is decomposed, it is absolutely necessary that the retort 

 should he made red-hot. — Orig. 



