Professor Silliman on the Fusion of Plumbago. 127 



than from charcoal ; so that they may be used with advantage 

 in class experiments, where the principal object is to exhibit 

 the brilliancy of the light. 



On examining the pieces in this and in numerous other 

 cases, I found them beautifully studded with numerous glo- 

 bules of melted plumbago. They extended from within a quar- 

 ter of an inch of the point, to the distance of \ or ^ of an inch 

 all around. They were larger than before and perfectly visi- 

 ble to the naked eye; they exhibited all the colours before 

 described, from perfect black to pure white, including brown, 

 amber, and topaz colours ; among the white globules, some 

 were perfectly limpid, and could not be distinguished by the 

 eye from portions of diamond. In different repetitions of the 

 experiment with the plumbago points, there were some vari- 

 eties in the results. In one instance only, was there a globule 

 formed on the point; it would seem as if the melted spheres 

 of plumbago as soon as formed, rolled out of the current 

 of flame, and congealed on the contiguous parts. In every 

 instance, the plumbago on the copper side was hollowed out 

 into a spherical cavity, and tlie corresponding piece on the zinc 

 side received an accumulation more or less considerable. In 

 most instances, and in all Avhen the deflagrator was very active, 

 besides the globules of melted matter, a distinct tuft or pro- 

 jection was formed on the zinc pole, considerably resembling 

 the melted charcoal described in my former communications, 

 but apparently denser and more compact ; although resembling 

 the melted charcoal, as one variety of volcanic slag resembles 

 another, it could be easily distinguished by an eye familiarized 

 to the appearances. In one experiment the cavit}', and all the 

 parts of the plumbago at the copper pole were completely 

 melted on the surface, and covered with a black enamel. The 

 appeai'ances were somewhat varied when specimens of plum- 

 bago from iliffercnt localities were used. In some instances it 

 burnt, and even deflagrated, being completely dissi2)ated in 

 brilliant scintillations; the substance was rapidly consumed 

 and no fusion was obtained. This kind of eilect occurred 

 most distinctly when there was a plumbago piece on the cop- 

 per side, ami a piece of charcoal on the zinc side. I have al- 

 reaily mentioned the curious result which is obtained wlien this 

 arrangement is reversed, the charcoal on the copper, and the 

 plunil)ago on the zinc side; this effect was now paiticularly 

 distinct and remarkable, — the charcoal on tJie cojiper side was 

 rapidly volatilized, a deep cavity was formed, and the charcoal 

 taken from it was instantly accunuilated upon die plumbago 

 point, forming a most beaiililul protuberance, completely di- 

 stinguishable from the plumbago, and presenting, when viewed 



by 



