382 Platina.—Cow-Tree. 
7. The cooling power of a gas varies with its temperature ; so 
that, if the gas can dilate so as to preserve the sane degree of 
elasticity, the cooling power will be found diminished by the rare- 
faction of the gas, just as much as it is increased by its being 
heated ; so that ultimately it depends upon its tension alone. 
It may be perceived, from the above propositions, that the law 
of cooling, composed of all the preceding laws, must be very com- 
plicated ; it is not therefore given in common language, but may 
be found in a mathematical form in the body of the memoir. 
PLATINA. 
A very singular mass of platinum has lately been found in South 
America, and is now deposited in the Royal Museum at Madrid. 
Dn. Ignacio Hurtado is the proprietor of certain lands in the 
Quebrada de Apoté, in the province of Notiva, in the govern- 
ment of Chocé. In this Quebrada is situated his gold mine, called 
Condoto. One of his Negro slaves, named Justo, found this 
mass of platina in the year 1814 near the goldmine. Dn. Igna- 
cio, most generously, and full of ardour for the sciences, pre- 
sented this unequalled specimen to His Most Catholic Majesty, 
through his excellency S* Dn. Pablo Morillo, commander-in- 
elvef of the Royal Spanish armies in the province of Venezuela, 
who transmitted the same, together with other objects of natural 
history, belonging to the botanical department, under the Spa- 
nish naturalist Dn. José Mutis, to Europe, through General 
Pascual Enrile, who brought it safely to Spain, and forwarded it 
to the hands of the King himself by Captain Antonio Van Halen. 
Being an unique specimen, his majesty gave it to the Museum. 
Its figure is oval, and inclining to convex. The Spaniards term 
it “ Pepita,” which signifies water-worn, and not im situ. 
Its large diameter is two inches four lines and a half, and its 
small diameter two inches. Its height is four inches and four 
lines. Its weight is one pound nine ounces and adrachm, Its 
colour is that of native silver. Its surface is rough, and here and 
there spotted with yellow iron ochre. The Negro who found it 
suspected that it contained gold: he tried to fracture it ; but he 
was only able to make a dent in the metal, which is, however, 
sufficient to show its character. 
To avoid every possible doubt about the mass of platina, it 
should perhaps have been mentioned, that the Spanish Secretary 
of State, his excellency Dn. José Garcia de Leon and Pizarro, 
had taken all the measures to ascertain the fact of its being ge- 
nuine native platina. 
€OW-TREE. 
M. Humboldt and his companions, in the course of their tra- 
vels, heard an account of a tree which grows in the valleys of 
Aragua, 
