Mr A. Robert,son''s Analysis nf Galena. ^t 



very fine powder, a hundred grains of which were digested in 

 three hundred grains of pure nitric acid, considerably diluted 

 with distilled water. W hen the action of the acid had ceased, 

 it was poured off, and replaced by two hundred grains of the 

 same acid similarly diluted, and the digestion was continued for 

 some hours longer. The two solutions, and the water with 

 which the undissolved matter was washed, were mixed together. 

 This residuary matter, after being well washed with distilled 

 water, was dried by exposure to the air, and gently heated for 

 some time by warm water placed under the vessel containing it. 

 The sulphur was then burnt off, and the loss of weight accu- 

 rately noted. The mean result of five experiments, from which 

 none of them varied two-tenths of a grain, was 12.37 grains. 



After the sulphur had been dissipated, there remained a 

 whitish powder, which, from several of its properties, was re- 

 cognized to be sulphate of lead. This had been formed, during 

 the analysis, owing to the oxidation of a small portion of the 

 sulphur by the nitric acid, although every precaution had been 

 taken to prevent it. A quantity of this, collected in the diffe- 

 rent experiments, was decomposed by boihng on it a solution of 

 carbonate of soda. The weight of sulphate of barytes which 

 this alkaline solution yielded, was nearly proportional to the 

 quantity of sulphuric acid, which, by calculation, the sulphate 

 contained ; and the carbonate of lead which was formed, dis- 

 solved completely with effervescence in diluted nitric acid, with 

 the exception of a little undecomposed sulphuret of lead. When 

 a solution of sulphate of soda was poured into this solution, it 

 afforded a quantity of sulphate of lead, only 4 per cent, less than 

 that of the original sulphate. After this had been separated, 

 the solution being supersaturated with carbonate of soda, a slight 

 pink tint appeared, which seemed to indicate manganese ; and 

 when tincture of galls was added, it also gave slight, though un- 

 equivocal, traces of iron. The average weight of this sulphate 

 of lead, in the three experiments from which the weight of the 

 lead was deduced, was eight grains, equivalent to 84 of a grain 

 of sulphur, and 5.47 grains of lead. 



The nitric acid solutions gave no trace of silver with muriate 

 of soda. From one of them the lead was precipitated by car- 

 bonate of ammonia, the precipitate being afterwards reduced ; 



