Dr. Wollaston on Platina 
190 
hopes that some account of it may be acceptable to the Royal 
Society, although the analysis must necessarily be very im- 
perfect, from the small quantity to which my experiments 
have unavoidably been confined. 
The general aspect of this specimen is so different from the 
common ore of platina, that I could form no conjecture of 
what ingredients it might be found to consist. Its appearance 
was such indeed, as at first sight to induce a suspicion of its 
not being in a natural state, for it had very much the spongy 
form which is given to platina from imperfect attempts to 
render it malleable by means of arsenic. 
One circumstance, however, occasions a presumption that 
no art has been employed in giving the grains their present 
appearance ; as upon close inspection many small particles of 
gold are discernible, but there is none of the magnetic iron 
sand with which the Peruvian ore abounds, nor any of the 
small hyacinths, which I have formerly noticed as accompany- 
ing that mineral.* 
It is very well known, that the common ore of platina in ge- 
neral consists of flattened grains, that appear so much worn at 
their surface, as to be in a considerable degree polished, and the 
roughness observable in some of the larger grains arises from 
concave indentations of a reddish brown or black colour. The 
Brasilian platina, on the contrary, has no polish, and does not 
appear worn ; but most of the grains seem to be small frag- 
ments of a spongy substance, and even those which are yet 
entire and rounded on all sides, present a sort of roughness 
totally different from that of the former, as their surface con- 
sists of 6inall spherical protuberances closely coherent to each 
* Phil. Trans, for 1805, p. 318. 
