126 Professor Sillinian on the Fusion of Plumbago. 



plmiibago was as rapidly elongated by matter accumulating at 

 its point, and which, when examined by the microscope, proved 

 to be a concretion in the shape of a cauliflower — of volatilized 

 and melted charcoal, having in a high degree all the charac- 

 teristics which I formerly described as belonging to this sub- 

 stance. Indeed, I found by repetitions of the experiment, that 

 this was the best mode of obtaining fine pieces of melted char- 

 coal. 



In some instances I used points of plumbago on botli poles, 

 and always obtained melted globules on both ; the results 

 were, however, not so distinct as when plumbago was on the 

 copper and charcoal on the zinc pole ; but the same elongation 

 of the zinc and hollowing of the copper pole took place as 

 before. I detached some of the globules, and partly bedding 

 them in a handle of wood, tried their hardness and firmness ; 

 they bore strong pressure without breaking, and easily scratch- 

 ed,* not only flint glass, but window glass, and even the hard 

 green variety which forms the aqua fortis bottles. The 

 globules 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 surfaces with a shining metallic-look- 

 ing 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 further at present ; as soon 

 as the zinc coils can be renewed, 1 shall hope to resume them, 

 and I entertain strong hopes, especially from the new impi'oved 

 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 deflagrator now 

 acts with great energy, and in consequence I have been enabled 

 to obtain good results when using plumbago upon both poles. 

 Parallelopipeds of that substance, i 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, transmit- 

 ted 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 em.itted 

 from the plumbago points, appeal's to be even more intense and 



rich 



