1823.] Scientific Intelligence, §||[ 



easily scratched, not only flint glass, but window glass, and even the 

 hard green variety, which forms the aqua fortjs bottles. The globule^ 

 which had acquired this extraordinary hardness, were formed from 

 plumbago which was so soft, that it was perfectly free from resistance 

 when crushed between the thumb and finger, and covered their surt 

 faces with a shining metallic looking coat. These globules sunk very 

 rapidly in strong sulphuric acid — much more so than the melted char- 

 coal, but not with much more rapidity than the plumbago itself, from 

 which they had been formed. 



*' The zinc of the deflagrator is now too far gone to enable me tfl 

 prosecute this research any farther at present. 



" April \2. — Having refitted the deflagrator with new zinc coils, I 

 have repeated the experiments related above, and have the satisfaction 

 of stating that the results are fully confirmed and even in some re- 

 spects extended. The deflagrator now acts with great energy, and ia 

 consequence I have been enabled to obtain good results when using 

 plumbago upon both poles. Parallelopipeds of that substance, one- 

 fifth of an inch in diameter and one inch or two inches long, being 

 screwed into the vices connecting the poles, on being brought into 

 contact, transmitted the fluid, with intense splendour, and became 

 fully ignited for an inch on each side ; on being withdrawn a little, 

 the usual arch of flame was formed for half an inch or more. Indeed 

 when the instrument is in an active state, the light emitted from the 

 plumbago points, appears to be even more intense and rich than from 

 charcoal ; so that they may be used with advantage, in class experi- 

 ments, where the principal object is to exhibit the brilliancy of the 



" On examining the pieces in this, and in numerous other cases, I 

 found them beautifully studded with numerous globules of melted 

 plumbago. They extended from within a quarter of an inch of the 

 point, to the distance of one-quarter or one-third of an inch all around. 

 They were larger than before and perfectly visible to the naked eye ; 

 they exhibited all the colours before described, from perfect black, to 

 pure white, including brown, amber, and topaz colours ; dmong the 

 white globules, some were perfectly limpid, and could not be distin- 

 guished by the eye from portions of diamond. 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 cur- 

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

 stance, the plumbago on the copper side, was hollowed out, into a 

 spherical cavity, and the corresponding piece on the zinc side, re- 

 ceived an accumulation more or less considerable. In most instances, 

 and in all when the deflagrator was very active, besides the globules 

 of melted matter, a distinct tuft or projection 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 cavity, and 

 all the parts of the plumbago at the copper pole were completely 

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

 pearances were somewhat varied when specimens of plumbago from 

 difierent localities were used. Ia some instances it burnt, and even 



