Dr. Wollaston on the Discovery of Palladium. 317 
scarcely to be distinguished or separated from them, excepting 
by solution of the platina ; for the grains of which I speak are 
wholly insoluble in nitro-muriatic acid. When tried by the file, 
they are harder than the grains of platina ; under the hammer 
they are not in the least degree malleable ; and in the fracture 
they appear to consist of laminae possessing a peculiar lustre ; 
so that although the greater number of them cannot, as I have 
before observed, be distinguished from the grains of platina, 
the laminated structure sometimes occasions an external form 
by which they may be detected. With a view to be absolutely 
certain that there exist grains in a natural state, which have 
not been detached by solution from the substance of the grains 
of platina, I have, separated from the mixed ore as many as 
enabled me to ascertain their general composition. 
Their most remarkable quality is their great specific gravity, 
which I have found to be as much as 19 5, while that of the 
crude grains of platina has not, in any experiment that I have 
made, exceeded 17 ,7 . F rom this circumstance it might naturally 
he; conjectured that they contain a greater quantity of platina 
than the grains in general ; by analysis, however, they do not 
appear to me to contain the smallest quantity of that metal, but 
take an ore consisting entirely of the metals that were found 
by Mr. Tennant in the black powder which is extricated by 
solution from the grains of platina, and which he has called 
Iridium and Osmium. But, since the specific gravity of these 
grains so much exceeds that of the powder, which by my ex- 
periments has appeared to be, at the utmost, 14,2, I have 
thought it might deserve inquiry whether their chemical com- 
position is in any respect different. For this purpose I have 
selected a portion of them, and have requested Mr. Tennant 
