96 WRITINGS OF JAMES SMITHSON. 



The open tube described by M. Berzelius in his valuable 

 work on the blowpipe, is adapted to the purpose by an addi- 

 tion to it. A small plate of platina foil, or a curved plate 

 of baked clay, is introduced a little way into one of its ends; 

 and secured by bringing with the point of the flame the glass 



into contact with it. The body to be tried is fixed to this 

 plate by means of moist clay; and may then be subjected 

 for any time to any degree of heat. 



Thus tried, fluor spar quickly obscured the glass by a thick 

 crust of siliceous matter ; and coloured yellow a bit of paper 

 tinged with logwood. 



M. Berzelius assigns fernambuc wood for the test of flu- 

 oric acid. Bergman says that this wood affords a red infu- 

 sion which alkalies turn blue.* None such could be 

 procured, but it was found that logwood might be substi- 

 tuted for it. The paper tinged with this, like that mentioned 

 by M. Berzelius, is made yellow by fluoric acid and oxalic 

 acid ; but it did not seem to be so by sulphuric or muriatic 

 acids, nor by phosphoric acid. 



Topaz. 



In extremely minute particles, topaz subjected to the fire 

 at the end of a very slender wire soon becomes opaque and 

 white ; but I perceived no marks of fusion. 



This change is undoubtedly occasioned by the loss of its 

 fluoric part. One of the times I was at Berlin, M. Klaproth 

 gave me, as his reason for not publishing the analysis of 

 topaz, that in the porcelain furnace it sustained a great loss 

 of weight, the cause of which he had not then been able to 

 ascertain. 



Topaz ground to impalpable powder, and blended with 

 carbonate of lime, melted with ease. Some of this mixture 



* Analysis of Mineral Waters. 



