378 
Mr Levy, Studies on Platinocyanides. 
Studies on Platinocyanides. By L. A. Levy, B.A., Clare College. 
\Read 25 November 1907.] 
The majority of platinocyanides exhibit fluorescent properties. 
The best of these salts in this respect is barium platinocyanide, 
which exhibits a green fluorescence under the action of ultra-violet 
light, X rays, radium rays, etc. In the course of some experiments, 
a quantity of this salt was prepared by double decomposition 
between the copper salt and baryta. The crystals are golden yellow 
and dichroic showing a purple sheen. They often exhibit red and 
green colours on the edges, especially when immersed in water. 
The fluorescence exhibited by the salt under ultra-violet light or 
radium is very poor. 
If this yellow salt be recrystallised from a solution to which 
very small amounts of certain substances have been added, a very 
marked difference is produced in the appearance of the salt and 
in the intensity of fluorescence which it exhibits. The experi- 
ments performed indicate that the properties of barium platino- 
cyanide are greatly affected by crystallising from solution with 
traces of certain impurities. The salt which crystallises out is 
green instead of yellow and markedly fluorescent. The experi- 
ments performed indicate that the production of the green salt 
may be determined by the presence of : 
(a) Potassium ions. 
( b ) Cyanogen ions. 
(c) Hydroxyl ions. 
(a) Potassium ions. This supposition, which appeared 
probable because many potassium salts were effective in producing 
the change, is disproved by the fact that barium cyanide and 
baryta are extremely efficient. 
(b) Cyanogen ions. This hypothesis was suggested by the 
following facts : 
(i) Substances yielding cyanogen ions have most effect. 
(ii) Unionised cyanides, e.g. mercuric cyanide, cyanogen 
iodide, have no effect. 
(iii) Substances yielding few cyanogen ions, e.g. potassium 
ferrocyanide and potassium thiocyanate, have a small effect. 
(c) Hydroxyl ions. This hypothesis, which appears to be 
the most probable, is justified because 
(i) Ionised cyanides produce large effects. All these are 
