296 philosophical transactions. [anno 1798. 



transparent quartzose sand, a soft opaque white earth, some particles of white mica, 

 and a quantity of dark lead-grey particles, which have a metallic lustre. The 

 Sydneia, N°2, appears chiefly to differ from N° 1, by being more arenaceous, and 

 by a larger proportion of the dark grey particles. Many experiments, similar to 

 those made on N° 1, already described, were made on this substance, with pure 

 concentrated muriatic acid ; but as none of these afforded any appearance of a pre- 

 cipitate by the means of water, I do not think it necessary to enter into a circum- 

 stantial account of them, and shall proceed therefore to the analysis. 



a. 100 grs. were exposed to a red heat, in a glass retort, and, after 4- an hour, 

 were found to have lost in weight 2.20 grs. — b. The 97-80 grs. which remained 

 were mixed with 300 grs. of dry carbonate of pot-ash, and the mixture was exposed 

 to a strong red heat, in a crucible of silver, during 3 hours. When cold, the mass 

 was softened with water, and was put into a glass matrass. I then added 3 oz. of 

 pure concentrated muriatic acid, and digested it for 2 hours in a strong sand heat. 

 Boiling water was then added, and the whole being poured on a filter, the residuum 

 was edulcorated, dried, and made red-hot ; it then weighed 85. bO grs. — c. The 

 filtrated solution was evaporated to -f, and pure ammonia being added, a precipitate 

 was formed, which, after a red heat, weighed 10.70 grs. — d. 1 oz. of muriatic acid 

 was poured on the IO.70 grs., in a matrass, which was then heated. The whole of 

 the 10.70 grs. was dissolved, excepting a small portion of siliceous earth, which 

 weighed 0.30 gr. 



e. The muriatic solution was then reduced by evaporation, to about ± ; to which 

 was added a large quantity of distilled water, which did not however produce any 

 change. I then gradually added a solution of pure crystallized prussiate of pot-ash, 

 and heated the liquor till the whole of the iron was precipitated ; after which, am- 

 monia precipitated a loose white earth, which, edulcorated and made red-hot, 

 weighed 7. 20 grs. The iron precipitated by the prussiate may therefore be esti- 

 mated at 3.20 grs. — f. The 7.20 grs. of the white earth were digested with sulphuric 

 acid, and, after the excess of acid had been expelled by heat, boiling water was 

 poured on the saline residuum. The solution was then gradually evaporated, with 

 the addition of a small portion of lixivium of potash, and afforded crystals of alum, 

 without a trace of any other substance. 



g. I now proceeded to examine the 85.50 grs. of b. These appeared to con- . 

 sist of siliceous earth, or fine particles of quartz, mingled with a considerable quan- 

 tity of the dark grey shining particles. Mr. Wedgwood was of opinion that these 

 were a peculiar species of plumbago or graphite. Professor Blumenbach, on the 

 contrary, regards them as molybdaena : and Mr. Klaproth believes them to be 

 eisenglimmer or micaceous iron ore. When rubbed between the fingers, they 

 leave a dark grey stain, and the feel is unctuous, like that of plumbago, or mo- 

 lybdaena : the traces which they make on paper also resemble those of the above- 

 mentioned substances, but the lustre of the particles approaches nearer to that of 

 molybdaena. 



