3 2 9 
Dr. Wollaston on the Discovery of Palladium. 
properties is not less remarkable, more especially in the little 
power they possess of conducting heat, and in the small degree 
of expansion to which they are liable when heated. 
For the purpose of making a comparison of the conducting 
powers of different metals, I endeavoured to employ them in 
such a manner, that the same weight of each metal might ex- 
pose the same extent of surface. With that view I selected 
pieces of silver, of copper, of palladium, and platina, which had 
been laminated so thin as to weigh each 1 o grains to the square 
inch. Of these I cut slips of an inch in breadth, and four 
inches long ; and having covered their surfaces with wax, I 
heated one extremity so as to be visibly red, and, observing 
the distance to which the wax was melted, I found that upon 
the silver it had melted as far as 3^ inches : upon the copper 2 \ 
inches : but upon the palladium and upon the platina only 1 
inch each : a difference sufficient to establish the peculiarity of 
these metals, although the conducting power cannot be said to 
be simply in proportion to those distances. 
In order to form some estimate of the comparative rate of 
expansion of these metals, I rivetted together two thin plates of 
platina and of palladium; and observing that the compound plate, 
when heated, became concave on the side of the platina, I ascer- 
tained that the expansion of palladium is in some degree the 
greater of the two. By a similar mode of comparison I found 
that palladium expands considerably less than steel by heat ; so 
that if the expansion of platina between the temperatures of 
freezing and boiling water be estimated at 9 parts in 10,000, 
while that of steel is known to be about 12, the expansion of 
palladium will probably not be much more or less than 10, or 
one part in 1000 by the same difference of temperature. 
Uu 
MDCCCV. 
