128 Professor Silliman on the Fusion of Plumbago. 



the microscope, a congeries of aggregated spheres, with every 

 mark of perfect fusion and with a perfect metallic lustre. I 

 would again recommend this arrangement when the object is 

 to attain fine pieces of melted charcoal. 



April l-i. — In repeating the experiments to-day, I have ob- 

 tained even finer results than before. The spheres of melted 

 plumbago were in some instances so thickly arranged as to re- 

 semble shot lying side by side ; in one case they com)iletely 

 covered the plumbago in the part contiguous to the point on 

 the zinc side, and were without exception white, like minute, 

 delicate concretions of mammillary chalcedony ; among a great 

 number diere was not one of a dark colour, except that when 

 detached by the knife they exhibited slight shades of brown at 

 tiie place where they were united with the general mass of 

 plumbago. They appeared to me to be formed by the con- 

 densation of a white vapour, which in all the experiments where 

 an active power was employed I had observed to be exhaled 

 between the poles and partly to pass from the copper to the 

 zinc pole, and partly to rise vertically in an abundant fume 

 like that of the oxide proceeding from the combustion of various 

 metals. I mentioned this circumstance in the report of my 

 first experiments (see vol. v. p. 112 of Silliman's Journal,) but 

 did not then make any trial to ascertain the nature of the sub- 

 stance. Although its abundance rendered the idea impro- 

 bable, I thought it possible that it might contain alkali derived 

 from the charcoal. It is easily condensed by inverting a glass 

 over the fume as it rises, when it soon renders the glass opaque 

 with a white lining. Although there was a distinct and pe- 

 culiar odour in the fume, I found that the condensed matter 

 was tasteless, and that it did not effervesce with acids, or affect 

 the test colours for alkalies. Besides, as it is produced ap- 

 jiarently in greater quantity, when both poles are terminated 

 by plumbago, it seems possible that it is white volatilized car- 

 bon, giving origin, by its condensation, in a state of greater or 

 less purity, to the grey, white, and perhaps to the limpid 

 globules. 



The deflagrator having been refitted only at the moment 

 when a part of this paper had already gone to the press, and 

 the remainder is called for, I am precluded by these ciicum- 

 stances from trying the decisive experiment of heating this 

 white matter by means of the solar focus in a jar of pure oxy- 

 gen gas, to ascertain whether it will produce carbonic acid 

 gas. 



This trial I have this morning made upon the coloured glo- 

 bules obtained in former experiments; they were easily de- 

 tached from the plumbago by the slightest touch from the 



point 



