[ 462 3 .

took 360 gfains of the larger and brighter particles pickedout from platina, and the fame quantity of the blackishdust separated from it by a sieve : the two parcels, in twosmooth scorifying dishes, were kept under a muffle, in avery strong heat, for five hours; and that both of themmight undergo an heat as equal as possible, the places ofthe two dishes were interchanged about the middle of theprocess. When cold, the picked platina, weighed withgreat exactness,, was found to have gained two grains, or.one part in a hundred and eighty ; while the dust was in-creased near nine grains, or one part in forty. It was ob-served that the picked platina had become darker colouredthan it was at first, but tire dust paler ; and that the pickedplatina cohered, very slightly, but the dust was agglutinated.,into a firm cake not easily to be broken between the fin-gers. It must be observed that what is here called dustcontains a considerable proportion of true platina, dividedinto particles as fine as those of the impure matter; andconsequently that the quantity of impure matter in thepicked platina cannot be judged of from the proportionalaugmentations which the two parcels received in the fire.But we shall here drop an enquiry, which does not. seemimportant enough to deserve the trouble of any furtherprosecution, especially as we shall hereafter find means ofattacking these calcinable parts more effectually than bysimple heat.

13. The experiments I had made (No. 5 and 6 of thisarticle) seem to prove, that platina cannot be brought in-to fusion in the common crucibles, by any heat that thevessels themselves can support. Mr. Scheffer concludesalso from his trials, that to melt it in a crucible is impossi-ble, since it resists even a stronger fire, than that which vi-trefies the best crucibles made ofWaldenburg earth andquartz,which we may suppose, from this manner of speak-