1823.] Scientific Litelligence, ilX 



of unmelted plumbago which might adhere to them T carefully rubbed 

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

 placed them upon a fragment of wedgewood ware, floated in a dish of 

 mercury, and slid over them a small jar of very pure oxygen 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 prepared lime-water ; the globules were now exposed to 

 the solar focus from the lens mentioned vol. v. p. 363. It was near 

 noon, and the sky but very slightly dimmed by vapour; although they 

 were in the focus for nearly half an hour, they did not melt, disap- 

 pear, or alter their form; it appeared however, on examining the gas, 

 that they had given up part of their substance to the oxygen, for car- 

 bonic 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 cha- 

 racter so highly vitreous, that they must necessarily waste away very 

 slowly, even when assailed by oxygen gas. In a long continued expe- 

 riment, it is presumable, that they would be eventually dissipated, leav- 

 ing only a residuum of iron. That they contain iron is manifest, from 

 their being attracted 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 

 afrit of white enamel, or looks a little 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 charcoal, 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 whether this white frit and these limpid spheres could arise from 

 carbon, volatilized in a white state even from charcoal itself, and con- 

 densed in a form analogous to the diamond. The rigorous and obvious 

 experiments necessary to determine this question, it is not now practi- 

 cable for me to make, and 1 must in the mean lime admit the jiossibility 

 that alkaline and earthy impurities may have contributed to the result. 

 ** In one instance contiguous to, but a little aside from the charcoal 

 points, I obtained isolated dark-coloured globules of melted charcoal, 

 analogous to those of plumbago. 



** The opinion which I formerly stated as to the passage of a cur- 

 rent from the copper to the zinc pole of the deflagrator, is in my view 

 fully confirmed. Indeed, with the protection of green glasses, my 

 eyes are sufficiently strong to enable me to look steadily at the flame, 

 during the whole of an experiment, and I can distinctly observe mat- 

 ter in different forms passing to the zinc pole, and collecting there, just 



