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XXVI. Notice of the Fusion of Plumbago, or Gra2Mte, 

 {commonlij called Black Lead,) in a Letter from Professoi- 

 SiLLiMAN to Professor Robert Hare, M.D. Dated March 

 26, 1823.* 



TN a former letter published in my Journal, (vol. v. p. 108,) 

 -*■ and in an additional notice, (p. 361 same vol.) I gave an ac- 

 count of the fusion and volatilization of charcoal, by the use of 

 your Galvanic Deflagrator. I have now to add, that the fusion 

 of plumbago was accomplished yesterday by the same instru- 

 ment, and that I have again obtained the same results to-day. 

 For this purpose, from a piece of very fine and beautiful plum- 

 bago, from North Carolina, I sawed small parallelopipeds, 

 about one eighth of an inch in diameter, and from three fourths 

 of an inch to one inch and a quarter in length : these were 

 sharpened at one end, and one of them was employed to point 

 one pole of the deflagrator, while the other was terminated by 

 prepared charcoal. Plumbago being in its natural state a 

 conductor, (although inferior to prepared charcoal,) a spark 

 was readily obtained, but in no instance of half the energy 

 which belongs to the instrument when in full activity ; for the 

 zinc coils were very much corroded, and some of them had 

 failed and dropped out; still the influence was readily convey- 

 ed through the remaining coils. As my hopes of success, in 

 the actual state of the instrument, were not very sanguine, I 

 was the more gi'atified to find a decided result in the very first 

 trial. To avoid repetitions, I will generalise the results. The 

 best were obtained when the plumbago was connected with 

 the copper, and prepared charcoal with the zinc pole. The 

 spark was vivid, and globules of melted plumbago could be 

 discerned, even in the midst of the ignition,yo7m«/j§- andformed 

 upon the edges of the focus of heat. In this region also there 

 was a bright scintillation, evidently owing to combustion, 

 wliich went on where air had free access, but was prevented by 

 the vapour of carbon, which occupied the highly luminous re- 

 gion of the focus, between the poles, and of the direct route 

 between them. Just on and beyond the confines of the ignited 

 portion of the plumbago, there was formed a belt of a reddish 

 brown colour, a quarter of an inch or more in diameter, which 

 appeared to be ov/ing to the iron remaining from the com- 

 bustion of the carbon of that part of the piece, and which, 

 being now oxidized to a maximum, assumed the usual colour 

 of the peroxide of that metal. 



In various trials, the globules were formed very abundantly 



* Silliman's Journal, vol. vi. p. 341. 



