380 
Mr Levy, Studies on Platinocyanides. 
“ The crystals of the two varieties of barium platinocyanide 
are identical cry stall ©graphically, and the angle of extinction in the 
plane of symmetry is in both cases very nearly in the direction of 
the longest edge which is selected in all descriptions as the 
vertical axis.” 
This report clearly shows that the differences cannot be 
determined by a difference of crystalline habit. 
Having regard to all the evidence, the hypothesis of two modi- 
fications of the same salt appears to be the most likely. One 
structural formula which has been proposed for platinocyanides 
is derived from complex double molecules of hydrocyanic acid. 
Thus 
N = C = C = N x 
Ba< >Pt 
X N - C = C = 
In this formula the barium and platinum are similarly situated. 
It does not show that the barium is exclusively basic and the 
platinum exclusively acidic, so that they are quite uninterchange- 
able. A solid model shows that there is only one possibility of 
isomerism on this formula — a kind of oxime isomerism represented 
graphically as follows : 
Ba N = C = C = N Pt 
= C = C = IT 
Ba 
N = 0 = C - N 
\n = C = C = N 
Pt 
This is a possible explanation of the existence of the two forms 
— the deposition of one being determined by alkali, that of the 
other by acid ; and the green form being the more stable. 
My thanks are due to Dr Fenton for valuable advice. 
