Professor Silliman on the Fusion of Plumbago. 129 



point of a knife, and, when collected in a white porcelain 

 dish, they rolled about like shot, when the vessel was turned 

 one way and another. To detach any portions of unmelted 

 plumbago which might'adhere to them, I carefully rubbed them 

 between my thumb and finger in the palm of my hand. I 

 then placed them upon a fragment of Wedgwood ware, floated 

 in a dish of mercury, and slid over them a small jar of very 

 pure oxj'gen gas, whose entire freedom from carbonic acid 

 had been fully secured by washing it with solution of caustic 

 soda, and by subsequently testing it with recently prejiared 

 lime-water; the globules were now exposed to the solar focus 

 fi'om the lens mentioned volume v. page 363. It was near 

 noon, and the sky but very slightly dimmed by vapour ; al- 

 though they were in the focus for nearly half an hour, they 

 did not melt, disappear, or alter their form ; it appeared, how- 

 ever, on examining the gas, that the}^ had given up part of 

 their substance to the oxygen, for carbonic acid was formed, 

 which gave a decided precipitate with lime-water. Indeed 

 when we consider that these globules had been formed in a heat 

 vastly more intense than that of the solar focus, we could 

 not reasonably expect to melt them in this manner, and they 

 are of a character so highly vitreous, that they must necessarily 

 waste away very slowly, even when assailed by oxygen gas. 

 In a long continued experiment, it is presumable that they 

 would be eventually dissipated, leaving only a residuum of 

 iron. That they contain iron is manifest, from their being at- 

 tracted by the magnet, and their colour is evidently owing to 

 this metal. Plumbago, in its natural state, is not magnetic, 

 but it readily becomes so by being strongly heated, although 

 without fusion, and even the powder obtained from a black 

 lead crucible after enduring a strong furnace heat, is magnetic. 

 It would be interesting to know, whether the limpid globules 

 are also magnetic ; but this trial I have not yet made. 



I have already stated, that the white fume mentioned above 

 appears when points of charcoal are used. I have found that 

 this matter collects in considerable quantities a little out of the 

 focus of heat around the zinc pole, and occasionally exhibits 

 the appearance of a frit of white enamel, or looks a litde like 

 pumice stone, only it has the whiteness of porcelain, graduating 

 however into light grey, and other shades, as it recedes from 

 the intense heat. In a few instances I obtained upon the char- 

 coal, when this substance terminated both poles, distinct limpid 

 spheres, and at other times they adhered to the frit like beads 

 on a string. Had we not been encouraged by the remarkable 

 facts already stated, it would appear very extravagant to ask 

 whetlier this white frit and these limpid spheres could arise 



Vol. (j'l. No. 30 1-. Aus. 1 823. R from 



