490 
PLATINA. 
power with which it resists the variations of the at- 
mosphere : most other metals sensibly contract in 
cold weather and dilate when it is warm ; but pla- 
tina is so little changed by different temperatures, 
that it has lately been made into rules, and applied 
by the geometricians Delambre and Mechain, when 
they measured a degree of the meridian in France. 
It is also of the first importance to philosophical 
chemists, when made into crucibles, &c., on account 
of its great infusibility. 
It appears from the account which Leblond has 
published in the Journal cle Physique for November 
1780, that platina is found only at Novita and 
Citara, in the province of Choco in South America. 
This province is situated in a deep and extensive 
valley, inclosed by the Andes ; from which circum- 
stance Leblond supposed that gold and platina were 
originally formed within these mountains, and that 
these metals, which are at present found in the val- 
ley, have been washed down from them in some of 
their decayed earth. “ It is rare in Choco,” says this 
naturalist, “ to meet with sandy earth without some 
particles of gold amongst it ; but it is only in the 
two districts of Citara and Novita that we find it al- 
ways mixed with platina.” 
Platina is always found in the form of very small 
particles, from the size of the smallest sand to that 
of a common pea ; the particles are detached from 
the earth with which they are mixed, with great 
care, being spread on a polished plate, and sepa- 
rated, grain by grain, with the blade of a knife. 
