164 Prof. Vanuxem's Experiments 



Experiment 3. — A specimen of plumbago from Borrowdale, 

 of great purity, as judged by its external characters and me- 

 chanical propeities, was subjected to the blowpipe : the glo- 

 bules began to form immediately and in great number, at- 

 tended occasionally by scintillations, owing to the combustion 

 of iron ; the globules were small ; the gi'eater part of them 

 were black, opaque, and of great lustre ; others were dull, of 

 a brownish colour, and feebly translucent : almost all of them 

 were attracted by the magnet. The surface of the heated 

 part of the plumbago was brownish. 



The globules, though acted upon with great difficulty by 

 soda, and by potash, readily yielded to the compound flux, 

 and formed a limpid yellowish glass. A large globule, by re- 

 peatedly heating it with cai'bonate of soda and plunging it 

 into water, became rough, and finally opened in the centre; 

 it then dissolved in nitro-muriatic acid. By evaporating the 

 liquor to dryness, the yellow colour of the iron was very mani- 

 fest; acidulated water took it up, leaving a white substance 

 like silex floating in the liquor. 



The analysis of this plumbago gave 



Carbon ' 88-37 



Water 1-23 



T5 -J 1 • • ^ rSilex 5"10 



Residue by mci-1 a i • i .nn 



neration, colour L^ ^ . . J ^lun^ine . . I'OO 

 yellowishbrick- >10-4 consistmg of^ Oxides of iron j 3.^^^ 



and manganesej 

 Loss 70 



100-00 



Experiment 4. — An impure specimen of plumbago from the 

 same locality gave numerous and large globules, some of the 

 size of small shot ; they readily formed : the majority of them 

 were translucent, shining, and of a light greenish-yellow ; 

 others were dark-coloured ; and some of them were dull ex- 

 ternally. The dark globules, as well as the surface of the 

 mass of plumbago exposed to the flame, were attracted by the 

 magnet; some of the light-coloured ones were affected by the 

 magnet, but only at the point where they had been attached to 

 their support, owing to particles of the support adhering to 

 them. During the combustion of the plumbago, there were 

 occasionally scintillations ; the heated surface of the mass was 

 brownish. 



A large globule of the lightest colour and magnetic only at 

 one point, melted with ease when tlie compound flux was used ; 

 it formed a transparent mass when hot, and opaque and milky 

 when cold. The black ones with the same flux were also 

 fused ; thev were brownish wjien hot. and greenish wlien cold. 



They 



