VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 20,7 



In order therefore to determine whether they consisted totally or partially of 

 molybdaena, I put the 85.50 grs. into a small glass retort, and added 2 oz. of con- 

 centrated nitric acid. The retort was then placed in a sand heat, and the distilla- 

 tion was continued, till the matter remained dry. The acid was then poured back 

 into the retort, and distilled as before ; but I did not observe that the grey particles 

 had suffered any change, nor were nitrous fumes produced, as when molybdaena is 

 thus treated. To be more certain however, I digested pure ammonia on the resi- 

 duum ; and having decanted it into a matrass, I evaporated it to dryness, without 

 perceiving any vestige of oxide of molybdaena, or indeed of any other substance. 



It was evident therefore that molybdaena was not present ; and as the general 

 external characters and properties corresponded with those of plumbago, I was in- 

 clined to believe that these were particles of that substance, and not micaceous 

 iron, as Mr. Klaproth imagined. To determine this, the following experiment 

 was made. 



h. 200 grs. of pure nitre in powder were mixed with the 85.50 grs., and the 

 mixture was gradually projected into a crucible, made strongly red-hot. A feeble 

 detonation took place at each projection; and, after a 4- hour had elapsed, the 

 crucible was removed. When cold, the mass was porous and white, without any 

 appearance of the dark grey particles. Boiling water was poured on it, and the 

 whole being put into a matrass, 1 oz. of muriatic acid was added, and digested with 

 it in a sand heat. By evaporation it became gelatinous : it was then emptied on a 

 filter, and being well washed, dried, and made red-hot, weighed 75.25 grs. The 

 appearance of this was that of a white earth, arid to the touch. When melted 

 with 2 parts of soda, a colourless glass was formed; and, with 4 parts of the same, 

 it was soluble in water, and produced liquor silicum ; it was therefore pure siliceous 

 earth. 



i. The filtrated liquor was saturated with ammonia, and, on being heated, a few 

 brownish flocculi were precipitated, which, when collected and dried, weighed 

 0.40 grs. This precipitate was dissolved in muriatic acid, and was again precipitated 

 by prussiate of pot-ash, in the state of Prussian blue. The liquor from which the 

 flocculi of iron had been separated was then examined, by adding carbonate of pot- 

 ash, and lastly, by being evaporated to dryness ; but it no longer afforded any 

 earthy or metallic substance : so that, by the process of detonation with nitre, the 

 85.50 grs. afforded 75.25 grs. of pure siliceous earth, with 0.40 gr. of iron ; and, 

 as the dark grey substance was destroyed, excepting the 0.40 gr. of iron above- 

 mentioned, and as Q.85 gr. of the original weight of 85.50 gr. were dissipated, 

 there can be no doubt but that this substance, amounting to 1 0.25 grs., was car- 

 buret of iron or plumbago ; especially as some experiments which I purposely made, 

 on that from Keswick in Cumberland, were attended with similar results. It is 

 also evident, that these particles could not be eisenglimmer or micaceous iron, as 

 nitre has little or no effect on that substance, when projected into a heated 

 crucible. 



VOL. XVIII. Q Q 



