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pltcoal: laid on a red hot iron, they etnitted a yellowishsmoke, and smelt like burning coal.

The foregoing observations afford some room to suspect,that this mineral has not come to us in its native form, buthas probably been ground in mills, and worked with quick-silver, in order to extract the particles of gold intermixedwith it. But its mineral history \Vill be considered moreparticularly after we have gone through the history of theexperiments, as some points cannot till then be sufficientlyunderstood. It is here only to be well attended to, thatall these matters are entirely adventitious to the platina;that their quantities are very variable, and that one or moreof them, in some parcels, seem to be altogether wanting,,the magnetic or ferrugineous matter being always the mostconsiderable, and possibly the only constant admixture.

III. Specific Gravity of Platina..

The mineral called platina being,, as we have beforeseen, a mixture of very dissimilar matters not uniformlyblended, I weighed hydrostatically several different parcels,taking sometimes four or five ounces for one experiment,and in one twelve ounces. In most of the trials, thegravity turned out, to that of water, very nearly as 17 to 1:it was never less than 16,500, nor greater than 17,200.The gravity of platina was examined also by Dr. Pernber-ton and Mr. Ellicott,who both reported it to be about 17.The late Mr. Sparkes informed me, that a specimen whichhe made trial of turned out but 16 ; and Dr. Davies, thathe weighed a parcel whose gravity was found to be 17,233.

To come as near as might be to the specific weight ofthe pure platina, I separated a quantity of the larger grainsby a coarse sieve, and endeavoured to cleanse them fromthe dust that might adhere, by boiling them in aquafortis,mixing them with sal ammoniac and forcing off the salt

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