VOL. XLVIIl.] PHILOSOPHICAL TRANSACTIONS. 51Q 



colour both internally and externally, and of a porous texture. It weighed about 

 -}- more than the quantity of platina employed. 



'2. This experiment was many times repeated and varied : the lead attempted 

 to be worked off on bone-ash, pressed into the bottoms of crucibles, scorified in 

 assay-crucibles, by intense fires, in a blast furnace, and blown off on tests before 

 the nose of a bellows, with the same event ; the platina not only perfectly resist- 

 ing the power of lead, which by these operations destroys every other known me- 

 tallic body, except gold and silver, but likewise retaining and preventing the 

 scorification of a part of the lead itself. 



3. In the history of the fusion of platina with lead, it has been observed, that 

 this metal deposites in a gentle heat great part of the platina, which had been 

 united with it by a strong one. As the part, which remained suspended, might 

 be presumed to differ from that which subsided ; a quantity of lead was decanted 

 off from fresh parcels of platina, and both the decanted metal and the residuum 

 submitted to tlie preceding operations separately. The event was still the same; 

 the matter becoming consistent when the lead had been worked off to a certain 

 point, and refusing further scorification. 



4. A mixture of platina and lead, which had been cupelled in an assay-furnace 

 as long as it could be kept fluid, was exposed in a crucible to a fire vehemently 

 excited, by itself, with powdered charcoal, with black fiux, borax, nitre, com- 

 mon salt. The matter neither melted nor suffered any considerable alteration, 

 becoming only somewhat more porous ; probably from a little of the lead having 

 exsuded without the liquefaction of the mass. The immediate contact of burn- 

 ing fuel, agitated by bellows, made some of these mixtures flow, after they had 

 refused to melt in vessels acted on by intense fires. Very little of the lead was 

 dissipated by this means. 



On examining the cupelled matters hydrostatically, those which appeared most 

 spongy were found nearly as ponderous as the crude platina. Among the more 

 compact, the gravity of one turned out 19.083 ; of another IQ.136, and of a 

 third 19.240. 



Remark. It appears from these experiments, that platina, like gold and silverii 

 is entirely indestructible by lead ; that probably the purer grains, or fragments, 

 have some heterogeneous admixtures, which are separated in these operations ; 

 and that, perfectly pure, it is more ponderous than gold, since, when mixed 

 with a considerable proportion of a lighter metal, it fell very little short of the 

 gravity of pure gold. There is no reason to suspect any increase of its specific 

 gravity from the mixture ; since in all the compositions with platina hitherto 

 examined, there was constantly a diminution of the specific gravity ; 'whether the 

 proportion of the platina was large or small, the matter melted with a quick fire, 

 or kept in fusion for many hours. ' 



