Mr. Bhown on the Analysis of Molybdate of Lead. 183 



The next thing to be obtained was the rest of the molybdic acid. This 

 was contained in the washings from the sulphuret of lead in the form of 

 ilphuret of molybdenum. When the solution was sufficiently concen- 

 trated, it was made slightly acid by means of hydrochloric acid, a brownish 

 coloured precipitate fell down, which was tersulphuret of molybdenum. 

 This was then thrown on a filter and washed. It was then dried at 212° 

 and weighed. Its weight was 3*37 grains. From this and the previous 

 quantity of molybdic acid, the quantity per cent, was calculated, which 

 was 39*30 grains. 



According to this analysis the composition of molybdate of lead is 



Molybdic acid, 39*30 



Protoxide of lead, 00*35 



99*65 



V. In the courso of the preceding analysis it was observed that the 

 suiphohydret of ammonia exercised a powerful solvent action on the 

 niiK'ral itself. The following new method of successfully analysing this 

 mineral was therefore adopted : — 



23*00 grains, after being reduced to a very fine powder, were digested with 

 the aid of gentle heat in suiphohydret of ammonia. The solution became 

 immediately of a deep red colour, owing to the tersulphuret of molybdenum 

 which is held in solution by the suiphohydret of ammonia, while the lead 

 was precipitated as sulphuret and fell to the bottom in the form of a black 

 powder. The clear supernatant liquor was then drawn off, and a fresh 

 portion of suiphohydret of ammonia was added. This after standing for 

 some time, was thrown on a filter, and washed with water containing 

 suiphohydret of ammonia. The tersulphuret of molybdenum passed 

 through in solution while the sulphuret of lead remained on the filter. 

 When this was completely washed, it was dissolved in dilute muriatic acid, 

 which takes up the lead and leaves the undecomposed matter along with 

 the sulphur. These were then thrown on a filter and washed. The whole 

 was then burnt. The sulphur was thus driven off while the insoluble 

 matter remained. The insoluble matter in 23 grains amounted to *24 

 grains, while in the former analysis it amounted to 1*15 in 26*84 grains. 



When the washings from the sulphur were sufficiently concentrated, the 

 lead was precipitated by means of ammonia and oxalate of ammonia. The 

 oxalate of lead was then thrown on a filter and washed. The quantity 

 of oxide of lead in 22*76 grains amounted to 13*71 grains, which is 

 niuivalcnt to 60*23 grains per cent. 



The next point was to precipitate the tersulphuret of molybdenum. 

 This was done by making the solution in suiphohydret of ammonia slightly 

 at id Ivy means of muriatic acid. The tersulphuret went down in the form 

 of a brownish coloured precipitate. This was then thrown on a filter, 

 dried, ignited, and weighed. The quantity in 22*76 grains was thus found 

 to be 9*91 grains, which is equivalent to 39*19 per cent, of molybdic acid. 



Vol. II.— No. 3. 4 



