Dr. Wollaston on a new Metal, 
428 
colour, that are very sparingly soluble in water. The corre- 
sponding salts of palladium, likewise resemble each other in 
every respect. The crystals are very soluble in water, but in- 
soluble in alcohol ; their form is that of a four-sided prism, and 
they each present a curious contrast of colour, that certainly is 
not observable in any known salt of platina. 
(G to.) Although the solution is of a deep red, the crystals 
are of a bright green when viewed transversely. In the direc- 
tion of their axes, however, the colour is the same as that of the 
solution ; but, on account of its extreme intensity, it is with diffi- 
culty distinguished in fragments that exceed T — of an inch in 
thickness. One consequence of this colour is nevertheless very 
observable ; namely, that in viewing any crystal obliquely, it 
appears of a dull brown, that arises from a mixture of the red 
and green.* 
The characters of palladium that have been enumerated, un- 
doubtedly belong to none of the simple substances that we. are 
* The change of colour above described, though certainly uncommon, is neverthe- 
less not peculiar to the salts of palladium, but may be seen also in some kinds of 
tourmalin. Among those which come to us from Ceylon, -some are transparent; and 
one variety is of a deep red in the direction of its axis, but of a yellowish-green when 
viewed transversely. There is also a corresponding, but opposite contrast of colours, 
that has been observed by Muller, and described by Bergmann, in some of the 
Tyrolese tourmalins. The general aspect of these stones is black, and apparently 
opaque. Some, however, of which the fracture is vitreous, are found to transmit a 
yellowish-red light when viewed transversely, but in the direction of their axis the 
colour is a dull bottle-green. 
In each of these tourmalins, as well as in the salts of palladium, the colour in the 
direction of the axis, is at least 10 times more intense thannn the transverse direction. 
A thin lamina, cut from the end of a Tyrolese tourmalin for this purpose, transmitted 
no visible light, till it was reduced to of an inch in thickness ; and, when less than 
of an inch, it was not more transparent than another portion of the same crystal 
seen transversely, of an inch in thickness. 
