166 PLATINA. 
particles. They are then piled with combustible sub- 
stances, and burnt or roasted, for the purpose of rid- 
ding them of the sulphur or arsenic with which they 
may happen to be combined, and which rises from them 
in a state of fume or smoke. Thus, having been freed 
from impurities, they undergo the operation of melting, 
in furnaces constructed according to the nature of the 
respective metab, or the uses to which they are to be 
subsequently applied. 
The knowledge of metals is a subject of great im- 
portance to mankind. Their use in trade is so frequent, 
and in the arts so various and so interesting, that few 
objects can be more worthy of attention than these. 
ORDER I. MALLEABLE METALS; 
OR, SUCH AS ARE CAPABLE OF BEING FLATTENED OR 
ELONGATED BY THE HAMMER, WITHOUT TEARING 
OR BREAKING. 
226. PLATINA, the most ponderous of all the metals 
with which we are acquainted, is, when purijied, about twenty 
times heavier than water. It is also one of the hardest and 
most difficult to be melted, is of white colour, but darker and 
not so bright as silver, and is found only in small blunted and 
angular grains or scales in the sands of some of the rivers in 
South America. 
If platina could be obtained in sufficient quantity, it 
would perhaps be the most valuable of all metals. The 
important uses to which it is applicable may easily be 
imagined when we state that it is nearly as hard as 
iron, and that the most intense fire and most powerful 
acids have scarcely any effect upon it. Platina is not 
fusible by the heat of a forge, but requires either the 
concentrated rays of the sun in a burning mirror, the 
