1817.] On the Decomposition of the Earths. 93 
metallic lustre like the metal of barytes. ‘The external appearance 
of the substance, after fusion, and before being rased by the file, is 
also like pure larytes that has been exposed to the same degree of 
temperature ; that is to say, it fuses into a globular form, which is 
of a jet-black colour, and shines with a considerable degree of 
metallic lustre. In all probability this metal is tantalum. 
5. Ancient Egyptian and Roman bronze Medals. — Having, 
upon a former occasion, alluded to the easy test afforded by this 
blow-pipe in distinguishing ancient bronze, from modern brass, and 
suspecting that the coins of the Romans in the second century 
might contain xinc, and therefore be of the latter description, I 
determined to submit to this test a medal of Marcus Aurelius Anto- 
ninus, and to compare its action before the ignited gas with the 
fusion of a bronze medal struck under the Ptolemies, in Egypt. 
There was, however, no perceptible difference ; the metallic com- 
pound, in either instance, consisting of copper alloyed with din. 
The fusion was tranquil, without any scintillation, or any deposit of 
zinc oxide upon the iron forceps used as a support. Afterwards, by 
placing the results in nitric acid, the copper was dissolved, and éia 
remained, in the form of a white precipitate; this precipitate being 
collected, washed, and dissolved in muriatic acid, afterwards pre- 
cipitated platinum from its solution in nitro-muriatic acid. I had. 
previously estimated the specific gravities of these alloys, and found 
them to be as follow :-— 
Bronze medal of the Ptolemies .............+. $2777 
Bronze medal of Marcus Aurelius Antoninus.... 8°6129 
6. Alloy of the Metal of Barytes with Silver.—I have before 
mentioned the appearance exhibited by this alloy. During two 
months it preserved its metallic appearance unaltered, and was so 
readily acted upon by the file, that | considered the silver as predo- 
minating, and that the metallic splendour, disclosed by rasing it, 
was mainly due to its presence; but at the expiration of the time I 
have mentioned, I found, to my great surprise, that the entire mass 
had assumed an earthy form, by mere exposure to atmospheric air 
in a warm and dry room; and that its particles, ceasing to cohere, 
had separated from each other; so that nothing remained of the 
alloy but the pulverulent appearance which had resulted from its 
disintegration. 
7. Vitrification of the Metals of the Earths, and some of the 
Semi-metals upon Charcoal.—\n all the experiments that I have 
made with the ignited gas where charcoal has been used for a sup- 
port, this inexplicable property has been more or less manifested. 
Pure Laryles, wixed with soot and /amp-oil, and placed within a 
cavity at the end of a stick of charcoal, instead of exhibiting the 
dark appearance, which during its fusion, per se, denotes its 
incipient reduction to the metallic state, becomes white, and 
assumes a vitreous aspect; but when the vitrified mass is taken 
out of the charcoal, and exposed alone to the ignited gas, fusion 
ensues, attended with combustion, scintillation, and the revival of 
the metal, Are we to conclude from this that the base of charcoal 
is itself medallic ? or that the metal is a compound body resulting 
