c 411 : 
XVI. On two Metals, found in the black Powder remaining 
after the Solution of Platina. By Smithson Tennant, Esq. 
F.R.S. 
Read June 21, 1804. 
Upon making some experiments, last summer, on the black 
powder which remains after the solution of platina, I observed 
that it did not, as was generally believed, consist chiefly of 
plumbago, but contained some unknown metallic ingredients. 
Intending to repeat my experiments with more attention during 
the winter, I mentioned the result of them to Sir Joseph Banks, 
together with my intention of communicating to the Royal 
Society, my examination of this substance, as soon as it should 
appear in any degree satisfactory. Two memoirs were after- 
wards published in France, on the same subject; one of them 
by M. Descotils, and the other by Messrs. Vauquelin and 
Fourcroy. M. Descotils chiefly directs his attention to the 
effects produced by this substance on the solutions of platina. 
He remarks, that a small portion of it is always taken up by 
nitro-muriatic acid, during its action on platina ; and, principally 
from the observations he is thence enabled to make, he infers, 
that it contains a new metal, which, among other properties, 
has that of giving a deep red colour to the precipitates of platina. 
M. Vauquelin attempted a more direct analysis of the sub- 
stance, and obtained from it the same metal as that discovered 
by M. Descotils. But neither of these chemists have observed. 
