258 Mr A. Robertson's Analysis of Galena. 



but the reduction was evidently incomplete, so that a portion of 

 lead was lost. A plate of zinc put into another threw down 

 metallic lead, but this was accompanied by a quantity of what 

 appeared to be a whitish oxide, so that this experiment also failed. 

 The remaining three solutions were neutralized by carbonate of 

 ammonia, and a solution of sulphate of ammonia was poured in, 

 in sufficient quantity to precipitate the whole of the lead which 

 they contained. The mean weight of the three parcels of sul- 

 phate of lead thrown down, after these had been well washed 

 and heated to low redness, was 115.7 grains, equivalent to 79-16 

 grains of lead. From this none of them varied half a grain. 



Carbonate of ammonia, and carbonate of soda, threw down 

 nothing farther from these solutions. 



As no ti'ace of silver was observed in these solutions, to de- 

 termine this point with greater accuracy, 1000 grains of the ore 

 were cupelled, until reduced to about twenty grains of lead. 

 These were dissolved in nitric acid. The solution did not lose 

 its transparency on the addition of a solution of muriate of soda, 

 and therefore contained no silver. 



Through the nitric acid solutions, from which the lead had 

 been separated, and wliich had been afterwards supersaturated 

 by an alkaline carbonate, sulphuretted hydrogen gas was trans- 

 mitted. A little of a brown precipitate subsided. About half 

 a grain of this, on charcoal before the blowpipe, gave out a 

 bluish flame, seemingly that of sulphur, and a globule re- 

 sembling fused oxide of iron remained. The most remarkable 

 feature was the very strong odour which it communicated to 

 the air of a pi'etty large apartment, and which was retained for 

 several hours. This smell was pungent, and, so far as could 

 be judged from recollection, bore some resemblance to that 

 smell of horse-radish which is stated to be the indication of se- 

 lenium. The presence of this substance, however, must be 

 doubtful, as in recognizing substances in this way there is very 

 considerable room for fallacy from various causes. 



To discover whether any iodine might be contained in the 

 ore, an ounce of it, reduced to a fine powder, was distilled in a 

 strong heat with an ounce of concentrated sulphuric acid. A 

 little sulphuretted hydrogen was first evolved, then some sul- 

 phur was sublimed, and a large quantity of sulphurous acid 



