VOL. XLVIII.] PHILOSOPHICAL TRANSACTIONS. 511 



3. One part of platina and 3 of silver still required a very strong fire for their 

 perfect fusion ; the metal was hard and brittle, though less so than the preceding: 

 when well and repeatedly nealed, it bore to be hammered, or flattened between 

 steel rollers, into thin plates. 



4. One part of platina and 7 of silver melted together with ease. This com- 

 pound hammered tolerably well, proved much harder than silver, and not so 

 white, or of so fine a grain. 



5. These compositions, weighed hydrostatically, turned out like the others, a 

 little lighter than by calculation; but the difference, which before seemed to in- 

 crease with the platina, was here greatest when the platina was in least pro- 

 portion. 



Specific gravity. 

 By experiment. By calculation. Difference. 



Platina 17.OOO 



Platina 1, silver 1 13,535 IS.ggO 0.455 



Platina 1, silver 1 12.452 12.987 0.535 



Platina 1, silver 3 11.790 12.485 O.695 



Platina 1, silver 7 IO.867 11 .732 0.865 



Silver IO.98O. , 



Remark. Platina appears to unite more difficultly with silver than with either 

 of the foregoing metals. Even when the proportion of the platina is small, the 

 greatest part of it subsides on an abatement of the heat, by which the union had 

 been effected. This was prevented by pouring out the metal, when perfectly 

 fluid, at one jet, into a broad mould: in which the compound began to congeal 

 before the platina could separate. 



Platina diminishes the malleability of silver far less than that of tin or lead; 

 and does not, in whatever proportion employed, so much debase its colour, or 

 dispose it to tarnish in the air. 



Art. 4. — Platina ivith Gold. 1 . Equal parts of platina and gold, exposed to 

 an intense fire, melted perfectly together, and ran thin into a long mould, with- 

 out loss. The metal was of a white colour, hard to the file, broke by a rude 

 blow, but when well nealed, yielded considerably to the hammer. 



2. One part of platina and 4 of gold came into fusion in a moderate fire, but 

 still required a very strong one for their perfect union. This compound appeared 

 but a little paler than standard gold with silver alloy; and proved so tough, as 

 to be beaten, with proper care, into thin plates, without breaking or cracking 

 about the edges. On melting it a second time with nitre and borax, it became 

 very pale, and was not without great difficulty made to recover its colour. 



yirt. 5. — Platina wit/i Copper. 1. Equal parts of platina and copper, exposed, 

 without addition, to a strong fire hastily excited by bellows, soon became fluid 



