510 PHILOSOPHICAL TRANSACTIONS. [aNNO 1754. 



crucibles closely luted, for 8 hours, suffered a diminution in weight, amounting 

 to about -jV of the lead. On breaking, those with a large proportion of platina 

 appeared of a leafy, and those with a smaller, of a fine fibrous texture, which 

 seemed in general to be characteristics of the perfect union of the platina and 

 lead. They all looked whiter and brighter than at first, but tarnished sooner in 

 the air. One mixture in particular, of 4 oz. of platina and 12 of lead, broke 

 into large, white, bright, shining, talc-like flakes; which, on exposure to the 

 air, changed in a little time to a reddish, a purple, and a deep blue; and at 

 length turned slowly to a dark blackish colour. 



10. On examining these compounds hydrostatically, their gravities turned out 

 less than they ought to have been according to their calculation, but not so much 

 less as those of the compositions of platina and tin. 



Specific gravity. 

 By experiment. By calculatiou. Difference. 



Platina 17.OOO 



Platina 1, lead 1 14.029 14.193 O.164 



Platina 1, lead 2 1 2.925 13.257 0.332 



Platina 1, lead 4 12.404 12.509 0.105 



Platina 1, lead 8 1 1-947 12.OO9 O.062 



Platina 1, lead 12 11.774 11.818 0.044 



Platina 1, lead 24 11.575 II.610. .... .0.035 



Lead 11.386. 



Remark. It appears, that a small proportion of platina is taken up and kept 

 suspended by lead, in a very gentle heat ; but that a large proportion is not taken 

 up near so easily as by tin ; and if united by a strong fire, subsides in part on its 

 abatement. A little quantity stiffens and hardens lead more than it does tin ; but 

 a large one does not near so much diminish its malleability. A leafy or fibrous 

 texture, a purplish colour, or disposition to acquire this colour in the air are 

 peculiar to the mixtures with lead. 



yirt. 3. — Platina with Silver. 1. Equal parts of platina and of pure silver 

 revived from luna cornea, covered with a borax, and urged with a strong fire in 

 a blast furnace, melted perfectly together, and without loss, but did not run 

 freely along the mould. The ingot was hard to the file, and broke by a rude 

 blow; though by gentle strokes it bore to be considerably flattened. Internally 

 it appeared of a much duller and darker colour than silver, and of a coarser 

 texture. 



2. One part of platina and 2 of silver, covered with nitre and common salt 

 did not flow thin till the fire was raised to a very strong white heat. The com- 

 pound proved less brittle than the foregoing, and not so hard to the file: the 

 texture was composed of smaller grains, and the colour whiter. 



