379 
Mr Levy , Studies on Platinocyanides. 
more or less hydrolysed by water in a warm solution yielding 
HCN and M + O'H. 
(ii) Alkalies are efficient in producing the change. 
It was found possible to reconvert the green salt, obtained as 
already described, to the yellow form by crystallising it out from a 
slightly acidified solution. It appears then that hydrogen ions may 
determine the deposition of the yellow form. 
The differences between the green and yellow forms may 
be due to: 
(a) A difference in chemical composition. 
( b ) A difference in the number of molecules of water of 
crystallisation. 
(c) The formation of a thin film of double salt. 
(d) A difference of crystalline habit. 
(e) A difference of molecular weight. 
(/) Isomorphous modifications of the same salt. 
Difference in chemical composition. Brochot and Petit pre- 
pared barium platinocyanide by electrolysis of a solution of barium 
cyanide between platinum electrodes, using an alternating current. 
The salt obtained is described by them as yellow, slightly 
dichroic and very slightly fluorescent under radium. They say 
that this product becomes fluorescent if crystallised out with 
cyanides. They have analysed the two forms and state that they 
both have the same composition, although they give very few 
figures in support of their analyses. 
The formation of a thin film of double salt is an unlikely 
explanation since the nature of the impurities effecting the change 
is very varied and different salts would be formed. There is no 
obvious reason why this should improve the fluorescence. 
Differences due to crystalline habit. 
Crystals of barium platinocyanide appear green along one axis 
and yellow along another axis. Possibly the two forms are due 
to a development along each of these axes. 
With a view to testing this hypothesis, experiments were 
made on the density and the crystalline characters of the two 
forms. The results obtained indicate that the density of the 
yellow form is rather less than that of the green modification, 
the mean values obtained respectively being 207G and 2 085 with 
respect to chloroform at 17° C. 
Prof. Lewis has kindly measured the two varieties of the salts 
and furnished the following report. 
