454 DR T. THOMSON'S Analysis of some Minerals. 



taken up. The undissolved matter, after ignition, weighed 0.25 

 grain. It was white and transparent, and, when viewed through 

 a glass, proved to be small grains of quartz, which had been me- 

 chanically mixed with the mineral. 



The solution, while hot, was mixed with an excess of bicar- 

 bonate of potash, previously dissolved in water, and the mixture 

 was digested on the sand-bath for 24 hours. The precipitated 

 carbonate of lead was then separated by the filter : after being 

 washed and dried, it was exposed to a red heat. It melted, as- 

 sumed a yellow colour, and weighed 18.52 grains. Being di- 

 gested in nitric acid, it dissolved, with the exception of a few 

 white flocks, which weighed, after ignition, 0.44 grain, and 

 proved, when examined by the blowpipe, to be silica. Hence 

 the oxide of lead was 18.08 grains, equivalent to 16.79 grains 

 of metallic lead. 



The alkaline solution, from which the carbonate of lead had 

 been thrown down, was evaporated to dryness, and the residue 

 digested in water. A small white powder remained undissolved. 

 By ignition it became yellow. It dissolved completely in nitric 

 acid, and the solution was precipitated orange by chromate of 

 potash. It was therefore oxide of lead. It weighed, after igni- 

 tion, 0.48 grain, equivalent to 0.445 grain lead. 



The alkaline solution was supersaturated with nitric acid, 

 and the sulphuric acid thrown down by muriate of bary tes. The 

 sulphate of barytes, obtained after edulcoration and ignition, 

 weighed 21.254 grains, equivalent to 2.881 grains of sulphur. 



Thus the constituents of the ore were, 



Lead, 17.235 or 86.175 



Sulphur, .... 2.881 . . . 14.405 

 Silica, '". ;";"'" 0690 ... 3.450 



29.806 104.030 



