VOL. XLVIII.] PHILOSOPHICAL TRANSACTIONS. 513 



large proportion of platina required the fire to be raised to a violent degree. Thig 

 seems owing, in good measure, to the platina preventing the scorification of the 

 cop})er; for on melting pure copper a great number of times, both with and 

 without fluxes, there was constantly a little loss. A small proportion of platina 

 appears to improve the hardness of copper, without injuring its colour, or, so 

 far as could be judged, its malleability. The mixtures with a large proportion 

 of platina are difficultly extended under the hammer when cold; and while red- 

 hot, fiy in pieces. They all bear a good polish, and do not tarnish in the air so 

 much, or so soon, as pure copper. 



Art. 6. — Platina with Iron. Iron, the last of the metals in point of fusibility, 

 was several times attempted to be united with platina, in its perfect malleable 

 state. But as the fluxes necessary for rendering forged iron fusible corroded the 

 crucibles, before the metal flowed thin enough to dissolve the platina, pure cast 

 iron was substituted. 



1 . Cast iron and platina, of each 3 oz. exposed without addition to a strong 

 fire, united into a thick fluid; which, on adding an ounce more of iron, flowed 

 thin, the compound suffered to cool in the crucible (which had become too soft 

 from the heat to admit of its being poured out) was found, on breaking the 

 vessel, in one lump, not convex, the form, which the iron usually assumes, but 

 of a very concave surface ; the weight about -gV less than that of the metals em- 

 ployed. It proved excessively hard, so as not to be touched by the file; and so 

 tough, as not to be broken by repeated blows of a sledge hammer, from which it 

 received some impression. Heated red, it broke easily, and looked internally of 

 a uniform texture, composed not of bright plates like the iron at first, but of 

 very dark-coloured grains. 



1. One ounce of platina being injected on 4 of cast iron beginning to melt, 

 and the fire kept up strong, the whole came quickly into fusion, and on cooling, 

 formed an equable compound, which like the former proved extremely hard, and 

 seemed to stretch a little under the great hammer without breaking. The colour 

 was still very dark, though less so than when the platina was in larger proportion. 



3. One part of platina and 12 of iron melted without difficulty, and with little 

 or no loss. This compound was still much harder than the iron at first, and 

 had a very considerable degi'ee of toughness. Like the others, it could not be 

 broken while cold, without extreme violence; but proved very brittle when 

 heated red. 



4. The foregoing compositions, especially those in which the proportion of 

 platina was large, received a fine polish ; and did not rust or tarnish on being 

 exposed to the air in a dry room for several months. 



5. A composition of 1 part of platina and 4 of iron was treated with sub- 

 stances, which produce notable alterations in pure iron. Surrounded with 



VOL. X. 3 U 



