514 PHILOSOPHICA.L TRANSACTIONS. [aNNO 1754. 



Reaumur's steel making mixture (composed of charcoal powder, soot, wood- 

 ashes, and common salt) and cemented in a close luted crucible for 12 hours, it 

 gained an increase of -j'^ its weight, yielded to the file more easily than at first, 

 seemed to receive no additional hardness on being ignited and quenched in water, 

 and discovered none of the qualities of steel. A piece broken off from the same 

 ingot, treated in the same manner, with the powder for softening cast iron (viz. 

 bone-ash, with a small proportion of charcoal) was found increased in weight 

 about -jVj proved less hard to the file than at first, but manifestly harder than 

 the part cemented with the steel-making mixture. 



Specific gravity. 

 By experiment. By calculation. Difference. 



Platina 1 7-000 



PlatinaS, iron 4 9-917 11.343 1.426 



Platina 3, iron 12 8. 700 9.O8O 0.380 



PlatinaS, iron 16 8.202 8.663 O.461 



Platina 3, iron 36 7. 800 7.862 O.062 



Iron 7.100. 



General Remarks. — Platina melts with equal its weight of each of the metals; 

 with one more readily than with another. With some it becomes fluid, if the 

 proportion of the platina is not large, in a moderate fire; but a strong one is 

 constantly requisite for its perfect solution. Compositions of silver, copper, lead, 

 with about ^ their weight of platina which had flowed thin enough to run freely 

 into the mould, and appeared to the eye perfectly mixed, on being digested in 

 aquafortis till the menstruum ceased to act, left several grains of platina in their 

 original form. On viewing these with a microscope, some appeared to have suf- 

 fered no alteration ; others exhibited an infinite number of minute bright globular 

 protuberances, as if they had just begun to melt. ' 



Platina hardens and stiffens all the metals ; one more than another, lead the 

 most. In a moderate quantity it diminishes, and in a large one destroys, the 

 toughness of all the malleable metals; but communicates some degree of this 

 quality to cast iron. Tin bears much the least, and gold and silver the greatest 

 quantity, without the loss of their malleability. 



A very small proportion of platina scarcely injures the colour of copper and 

 gold: a larger renders both pale; a far less quantity has this effect on copper 

 than on gold. It debases and darkens, in proportion to its quantity, the colour 

 of the white metals; that of silver much the least, and of lead the most. It 

 in good measure preserves iron and copper from tarnishing in the air; scarcely 

 alters gold or silver in this respect; makes tin tarnish soon, and lead exceeding 

 quickly. 



PAPER IV. — Platina mixed with Semimetals. 1. With mercury. 1, An 



