Mr. Smithson on 



[Feb. 



102 



M. Berzelius assigns fernambuc wood for the test of fluoric 

 acid. Bergman says that this wood affords a red infusion 

 which alkalies turn blue.* None such could be procured, but it 

 was found that logwood might be substituted 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 car- 

 bonate of lime, melted with ease. Some of this mixture fused 

 on the platina plate at the mouth of the tube, made an abundant 

 deposit of silica over its interior surface ; and the bit of logwood 

 paper at the end of it had its blue colour altered to yellow. 



In the trial in this way of substances of difficult fusion, an 

 apparatus of the following construction is more favourable than 

 the one above described. 



a. A bottle coik. 



It. A slice of the same fixed with three pins. 



c. A wire. 



* Analysis of Mineral Waters. 



