VOL. LXXX.] PHILOSOPHICAL TRANSACTIONS. 673 



brought into perfect fusion, in contact with inflammable matter, and in close 

 vessels, it does not assume the appearance which metallic bodies do in that cir- 

 cumstance. 



The black particles, which bore but a very small proportion to the other mat- 

 ter, were in form of shining black scales, very thin, and very light. One grain 

 weight of them, carefully picked out, exposed to a fire which was gradually raised 

 to about 90°, and continued in all about 40 hours, in a vessel loosely covered, was 

 almost wholly dissipated, and what little remained was perfectly white. Marine 

 acid had no effect on it. Fifteen grains of the entire mineral lost, in the same 

 fire, 3 grains. After separating from another portion of the mineral, by washing 

 and otherwise, a considerable quantity of the white matter, 15 grs. of the re- 

 mainder, continuing of course more than its due proportion of the black, lost 

 5 grains ; so that it seems principally to be the substance on which the blackness 

 depends that is destroyed or dissipated by fire. The same quantity, 15 grains, of 

 common black-lead lost in the same fire above 14 grs. the residuum weighing less 

 than 1 grain. Though no conclusion can be drawn from these experiments re- 

 specting the comparative loss of black-lead and the pure black matter of this 

 mineral, on account of the heterogeneous parts intermixed with the latter, the 

 colour of the residua seems to afford a sufficient discrimination between them ; 

 that of black-lead being dark reddish brown, but the others purely and uniformly- 

 white. 



As this substance could not now be supposed to be either iron mica, or the 

 common kind of black-lead, suspicion fell on molybdaena. Mr. W. had not, at 

 that time, had an opportunity of procuring a specimen of molybdaena to compare 

 it with ; but from the singular and strongly-marked properties of the molybdaenic 

 acid, discovered by Scheele, it was judged, that a very small quantity of it, when 

 disengaged from the sulphur with which it is naturally combined, would easily be 

 distinguishable. Hjelm's process for disengaging the sulphur, by repeatedly 

 burning linseed oil on the molybdaena in a crucible, and afterwards abstracting 

 successive quantities of the same oil from it in a retort, was tried on a portion of 

 the Sydney-Cove mineral, from which much of the white matter had been sepa- 

 rated as above-mentioned. The black coal, remaining in the retort, became 

 yellow by calcination, as that of molybdaena should do; but in this yellow powder, 

 no vestige of molybdaenic acid could be discovered. 



Another quantity of the mineral was submitted to Scheele's own process, viz. 

 repeated abstractions of diluted nitrous acid ; but instead of becoming whiter 

 every time, and at length white as chalk, which molybdaena should do, the 

 blackness of this matter continued unaltered to the last. There is one circum- 

 stance in Mr. Scheele's experiments, which, though omitted by those who have 

 given abstracts of them, may deserve, on the present occasion, to be more parti- 



VOL. XVI. 4 R 



