344 Fimon of Plumbago. 



ly bedding them in a handle of wood, tried their hardness 

 and firmness; they bore strong pressure without breaking, 

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

 and even the hard green variety, which forms the aqua for- 

 tis bottles. The globules which had acquired this extraor- 

 dinary hardness, vi^ere formed from plumbago which was so 

 soft, that it was perfectly free from resistance when crush- 

 ed between the thumb and finger, and covered their surfa- 

 ces with a shining metallic looking coat. These globules 

 sunk very rapidly in strong sulphuric acid — much more so 

 than the melted charcoal, 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 to prosecute this research any farther at present; as soon 

 as the zinc coils can be renewed, I shall hope to resume 

 them, and I entertain strong hopes, especially from the new 

 improved and much enlarged deflagrator, which you are so 

 kind as to lead me soon to expect from Philadelphia. 



April 12. — 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 respects extended. The De- 

 flagrator now acts with great energy, and in consequence I 

 have been enabled to obtain good results when using Plum- 

 bago upon both poles. Parallelopipeds of that substance, { 

 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 

 splendor, 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 on being withdrawn a little, the usual arch of flame was 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 instru- 

 ment is in an active state, the light emitted from the plum- 

 bago points, appears to be even more intense and rich 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 peices in this, and in numerous other 

 cases, 1 found them beautifully studded with numerous glo- 

 bules of melted plumbago. They extended from within a 

 quarter of an inch of the point, to the distance of ^ or | of an 

 inch all around. They were larger than before and per- 



