296 BUNSEN ON THE CACODYL SERIES. 
dered very impure from a large mixture of the oxide. It is also 
extremely difficult to purify it by crystallization, as the latter is 
easily oxidized and the cyanuret is so truly fearful as a poison. 
Its production will be understood from the following equation :— 
Kd O a a 3) 
H Cy 
It affords an example of a very common phenomenon attend- 
ing the ordinary decomposition of inorganic oxides. The sub- 
stance which was submitted to the following inquiries was pre- 
pared in a much shorter and less dangerous way. On mixing 
a concentrated solution of cyanide of mercury with oxide of ca- 
codyl, the mercury is deposited, this cyanogen compound formed, 
and the other portion of the oxide is more highly oxidized. Not 
the least trace of prussic acid or oxide of cacodyl passed over on 
distillation, and the only impurity mixed with the cyanide of 
cacodyl is the higher oxide of cacodyl. The cyanide forms a 
yellow oily layer under the water; after a short time nearly the 
whole crystallizes in large well-formed prisms, which sometimes 
shoot up into the water lying above. The water and the liquid 
portion is poured off, and the crystals dried between folds of 
blotting paper. It is absolutely necessary to conduct this opera- 
tion in the open air, and to respire through a long glass tube 
which passes out of the influence of this volatile cyanide. 
The crystals obtained possess quite a diamond lustre, and are 
nearly pure: they must be melted, freed from water by means 
of barytes in the distillation tube filled with carbonic acid, and 
about one-half distilled. The distilled portion contains traces 
of foreign matters, and in order to separate these I pursued the 
following plan. The leg of the distillation tube containing the 
anhydrous crystals is broken off, and they are immediately trans- 
ferred into one end of a glass tube, bent at right angles, and 
filled with carbonic acid. The open end of the glass tube must 
be quickly melted: the shorter end of the glass tube containing 
the crystals is immersed in water heated to 50° or 60° C., when 
the crystals melt, and by allowing the liquid to cool very slowly, 
it crystallizes in large prisms, which are surrounded by a por- 
tion of the fluid. When two-thirds of the whole has crystallized 
the remaining liquid portion is poured into the longer leg of the 
glass tube. This is repeated as long as the liquid has a yellow 
colour ; and when this disappears, the portion remaining in the 
short 2 of the glass tube may be regarded as perfectly pure. 3 
ent nw 
