68 WRITINGS OF JAMES SMITIISON. 



carbonate of soda at hand, I added a particle of nitre, whos© 

 deflagration producing potash, lead was revived. 



A bit, which had been made white by ignition, being 

 wetted with nitrate of cobalt and again ignited, became 

 blue. 



Heated in a glass tube over a candle, it decrepitated, be- 

 came opaque and white, and water sublimed. 



Mr. Tonnant mentioned to me a sort of explosion occa- 

 sioned by the sudden expulsion of the water, and charactcr- 

 ifltic of this ore, which took place when it was heated at the 

 blow-pipe. With the very minute particles I have tried, no 

 effect of this sort was perceived. 



The above characters will prove sufficient, I apprehend, 

 to make this substance known when met with. 



Prom Thomson's Anniila of Philosophy, Vol. XVI, 1820, p. 100. 



PLomb Oomvie. — Mr. Smilhson has given us somo interesting details 

 respecting tlio history and properiies of this mineral, which is a hydrous 

 aluminate of lead. It has a yellow colour, and is exceedingly eimiiar in 

 appearance to Mullen glass. When heated, it docrtjpitatos violently ; and 

 if it bo heated by the blow-pipo, in contact with an alkali, lead is reduced. 

 Its nature was first ascertained by Mr. Tennunt. Berzolius has lately anal- 

 yzed it. The result of his analysis will bo found in the Annals of Philoso- 

 phy, xiii. 881. (Sec Aimals of Philosophy, xiv. 81.) 



ON A FIBROUS METALLIC COPPER. 



From Thomson's Annals of Philosophy, Vol. XVI, 1820, p. 40. 



Paris, 3Iarch 17, 1820. 



Sir : There occur, in mineral collections, pieces of a cop- 

 per slag, having fibres of metallic copper in its cavities. I 

 have seen this fibrous copper erroneously placed among 

 native coppers. 



I possess samples of this kind from a foundery in the 

 Ilartz. The metallic copper in the cavities, or air-holes, is 

 80 delicately slender as to bo a metallic wool. 



