1835.] Chemical Analysis of Thulite. 95 



for ten minutes in a covered platinum crucible. The glass 

 was dissolved in nitric acid, and the silica separated in the 

 usual way. The lead was then thrown down by sulphuric 

 acid, and the last portions of it by sulphuretted hydrogen 

 gas. The oxides of cerium, of iron, and the lime, were 

 then thrown down by carbonate of ammonia. The residual 

 liquid was evaporated to dryness, and the ammoniacal 

 salts driven off by heat, a salt remained, which after solu- 

 tion, evaporation, and ignition, was found to weigh 6*87 

 grains, but it was impure. After some attempts to purify 

 it I mixed it with chloride of platinum, (after converting it 

 into chloride,) and alcohol, and evaporated to dryness. The 

 dry yellow residue was digested in common spirits, and after 

 every thing soluble was taken up, I dried the potash 

 chloride of platinum, and exposed it to a very strong red 

 heat. By this means the platinum was reduced to the 

 metallic state. It was weighed, and from the amount of 

 weight, that of the potash chloride of platinum was deter- 

 mined. The quantity of potash indicated was almost exactly 

 2 grains, which amounts to 8 per cent. Hence, the consti- 

 tuents of thulite are 



atoms. 



Silica 46-10 „ 23-05 



Peroxide of cerium - - 25-95 ,, 3*7 



Lime 12-50 „ 357 



Potash 8-00 „ 1-33 



Peroxide of iron - - - 5*45 ,, 1*1 

 Moisture ------ 1-55 „ 1-38 



99-55 



The atoms of silica amount to 23*05, while those of all 

 the bases are 9-7. So that if we consider the mineral as 

 composed of bisilicates, there is an excess of 3*65 atoms. 

 This excess however is easily accounted for. The thulite 

 analyzed was interspersed with numerous grains of silica, 

 varying in size from that of a pea to an almost microscopic 

 globule. Though I was at the utmost pains to exclude 

 these grains from the portion subjected to analysis, and 

 carefully picked out all the pieces of thulite, which appeared 

 free from silica when viewed through a microscope, yet, in 

 consequence of the extreme minuteness of the silica, it was 

 impossible to exclude the whole. Hence the reason of the 



