1823.] Scientific Intelligekce. ^V 



I expect it, but I wished to compare this old experiment with those 

 related above. 



The diamond is now the only substance which has not been perfectly 

 melted. 



I inserted a piece of plumbago into a cavity in quick lime, and suc- 

 ceeded in melting it down by the blow-pipe into two or three large 

 globules, adhering into one mass, and occupying the cavity in the 

 lime ; these globules were limpid ; and nothing remained of the origi- 

 nal appearance of the plumbago except a few black points. 



The subject is concluded at p. 378, of the Journal, by the addi- 

 tional notice isubjoined, dated April 23. 



If melted charcoal, plumbago, and anthracite do really approximate 

 towards the character of diamond, we ought to expect that, in conse- 

 quence of fusion, there would be a diminution of conducting power, 

 with respect both to heat and to electricity. This I find to be the 

 fact. As soon as the point of charcoal is fused by the deflagrator, the 

 power of the instrument is very much impeded by it ; but as soon as 

 the melted portion is removed, the remaining charcoal conducts as 

 well as before ; and so on, for any number of repetitions of the expe- 

 riment, with the same pieces of charcoal. 



The globules of melted plumbago are absolute non-conductors, as 

 strictly so as the diamond. This fact is very pleasingly exhibited, 

 when a point of prepared charcoal, connected with the zinc pole of 

 the deflagrator, is made to touch a globule of melted plumbago, how- 

 ever small, still adhering to a parallelepiped of plumbago, in its natu- 

 ral state, screwed into the ,vice connected with the copper pole ; not 

 the minutest spark will pass ; but if the charcoal point be moved, ever 

 so little aside, so as to touch the plumbago in its common state, or 

 even that which has been ignited, without being fused, a vivid spark 

 will instantly pas^. This fact is the more remarkable, because it is 

 equally true of the intensely black globules which are sensibly mag- 

 netic, and therefore contain iron, as of the light coloured and limpid 

 ones, which are not attractable. 



The globules of melted anthracite are also perfect non-conductors. 

 This may appear the less remarkable, because the anthracite itself is 

 scarcely a conductor ; at least, this is the common opinion ; and it cer- 

 tainly is strictly true of that of Wilkesbarre and of that of Kilkenny ; 

 for when both poles are tipped with those substances, there is only a 

 minute spark, which is but little augmented when charcoal terminates 

 one of the poles. But the fact is remarkably the reverse with the 

 Rhode-Island anthracite ; this conducts quite as well as plumbago, 

 and I think even better, giving a very intense light, and bright scin- 

 tillations. I have now no doubt that the deflagrator will melt it, but 

 have not had time to complete the trial. 



If it should be said that the conducting power of the Rhode-Island 

 anthracite may be owing to iron, we are only the more embarrassed 

 to account for the fact, that its black melted globules are insensible to 

 the magnet, and are perfect non-conductors. 



It will now probably not be deemed extravagant, if we conclude 

 that our melted carbonaceous substances approximate very nearly to 

 the condition of diamond. 



