1813.] Analysis of Graphite. 29 J' 



♦ 



slight shade of blue. The residue being exposed to a strong 

 heat, and re-dissolved in water, there fell 2 graius of a greyish 

 powder, which, by a method to be described afterwards, 1 sepa- 

 rated into 0-2 grain of oxide of copper, 1-3 grain of oxide of 

 titanium, and 0*5 grain of oxide of iron. 



C. 



Partly in order to estimate these constituents with still greater 

 precision, and partly to ascertain the composition of English 

 graphite with still more accuracy, I undertook the examination 

 pi another specimen of English compact graphite, which I 

 knew for certain to have been obtained out of the mine of Bar- 

 rowdale. 



1. This graphite was reduced to a fine powder, and boiled 

 with water. The liquid continued colourless, but acquired a 

 strong taste of clay. It produced no change upon litmus paper, 

 and prussiate of potash produced no perceptible change in it. 

 With tincture of nutgalls it exliibited a slight tendency towards 

 a reddish brown colour, which was increased by tlie addition of 

 jcarbonate of soda, and at last passed into greenish brown. No 

 precipitate fell. Caustic ammonia produced no aheration in it. 

 Muriate of barytes rendered it opalescent, and sligiitly muddy. 

 The muddiness was not removed by nitric acid; but the precipi- 

 tate that fell was so small that it could not be weighed. Nitrate 

 of silver likewise occasioned an opalescence ; but no precipitate 

 fell. 



2. Two hundred grains of the graphite thus boiled in water 

 were burnt in a silver crucible with ten times their v^^eight of 

 saltpetre. A considerable time elapsed before the combustion 

 took place. After the saljne residue had been washed away in 

 water, there remained behind 34*4 grains of a light brov^^n 

 powder. From the saline solution, by means of an acid and 

 carbonate of soda, 1 grain of alumina was separated. It was 

 still mixed with a small quantity of oxide of iron. 



3. The light brown powder was boiled in nitro-muriatic acid. 

 A portion remained undissolved, which had a greyish colour; 

 but in other respects resem.bled silica. This residue, while still 

 moist, was boiled in an alkaline ley. A brownish black powder 

 soon separated from it, which w-eighed 3*6 grains. 



4. The acid solution of paragraph 3 was diluted with water. 

 A white powder separated, which weighed 0*2 grain. This was 

 mixed with the 3*6 grains of the brownish black powder of 

 paragraph 3, and heated to redness in a platinum crucible with 

 a little carbonate of soda. The whole dissolved in muriatic acid, 

 and the solution had a greenish yellow colour. The solution 

 being neutralised with ammonia, and treated with prussiate of 

 potash and tincture of nutgalls, exhibited the appearances pro- 

 duced by a solution of titanium* 



